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NetBSD/sys/kern/kern_entropy.c

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entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/* $NetBSD: kern_entropy.c,v 1.63 2023/08/04 07:38:53 riastradh Exp $ */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*-
* Copyright (c) 2019 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Taylor R. Campbell.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Entropy subsystem
*
* * Each CPU maintains a per-CPU entropy pool so that gathering
* entropy requires no interprocessor synchronization, except
* early at boot when we may be scrambling to gather entropy as
* soon as possible.
*
* - entropy_enter gathers entropy and never drops it on the
* floor, at the cost of sometimes having to do cryptography.
*
* - entropy_enter_intr gathers entropy or drops it on the
* floor, with low latency. Work to stir the pool or kick the
* housekeeping thread is scheduled in soft interrupts.
*
* * entropy_enter immediately enters into the global pool if it
* can transition to full entropy in one swell foop. Otherwise,
* it defers to a housekeeping thread that consolidates entropy,
* but only when the CPUs collectively have full entropy, in
* order to mitigate iterative-guessing attacks.
*
* * The entropy housekeeping thread continues to consolidate
* entropy even after we think we have full entropy, in case we
* are wrong, but is limited to one discretionary consolidation
* per minute, and only when new entropy is actually coming in,
* to limit performance impact.
*
* * The entropy epoch is the number that changes when we
* transition from partial entropy to full entropy, so that
* users can easily determine when to reseed. This also
* facilitates an operator explicitly causing everything to
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
* reseed by sysctl -w kern.entropy.consolidate=1.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* * Entropy depletion is available for testing (or if you're into
* that sort of thing), with sysctl -w kern.entropy.depletion=1;
* the logic to support it is small, to minimize chance of bugs.
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
*
* * While cold, a single global entropy pool is available for
* entering and extracting, serialized through splhigh/splx.
* The per-CPU entropy pool data structures are initialized in
* entropy_init and entropy_init_late (separated mainly for
* hysterical raisins at this point), but are not used until the
* system is warm, at which point access to the global entropy
* pool is limited to thread and softint context and serialized
* by E->lock.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
#include <sys/cdefs.h>
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.63 2023/08/04 07:38:53 riastradh Exp $");
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
#include <sys/param.h>
#include <sys/types.h>
#include <sys/atomic.h>
#include <sys/compat_stub.h>
#include <sys/condvar.h>
#include <sys/cpu.h>
#include <sys/entropy.h>
#include <sys/errno.h>
#include <sys/evcnt.h>
#include <sys/event.h>
#include <sys/file.h>
#include <sys/intr.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/kthread.h>
entropy(9): Include <sys/lwp.h> and <sys/proc.h> explicitly. Now that we use curlwp, struct lwp::l_pflag, and LP_BOUND, let's not rely on side-loads from other .h files.
2022-03-24 02:20:52 +03:00
#include <sys/lwp.h>
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
#include <sys/module_hook.h>
#include <sys/mutex.h>
#include <sys/percpu.h>
#include <sys/poll.h>
entropy(9): Include <sys/lwp.h> and <sys/proc.h> explicitly. Now that we use curlwp, struct lwp::l_pflag, and LP_BOUND, let's not rely on side-loads from other .h files.
2022-03-24 02:20:52 +03:00
#include <sys/proc.h>
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
#include <sys/queue.h>
entropy: Only print consolidation warning of AB_DEBUG. The previous fix for PR kern/55458 changed printf to log(LOG_DEBUG, ...) with the intent of hiding the message unless 'boot -x'. But this did not actually suppress the message to console as log(LOG_DEBUG, ...) will print to console if syslogd is not running yet. So instead, just check for AB_DEBUG flag directly in boothowto, and only printf the message if it is set.
2021-02-12 22:48:26 +03:00
#include <sys/reboot.h>
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
#include <sys/rnd.h> /* legacy kernel API */
#include <sys/rndio.h> /* userland ioctl interface */
#include <sys/rndsource.h> /* kernel rndsource driver API */
#include <sys/select.h>
#include <sys/selinfo.h>
#include <sys/sha1.h> /* for boot seed checksum */
#include <sys/stdint.h>
#include <sys/sysctl.h>
entropy: Downgrade consolidation warning from printf to LOG_DEBUG. Candidate fix for PR kern/55458. This message is rather technical, and so is unlikely to be acted on by anyone not debugging the kernel anyway. Most likely, on any system where it is a real problem, there will be another (less technical) entropy warning anyway.
2021-01-11 05:18:40 +03:00
#include <sys/syslog.h>
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/xcall.h>
#include <lib/libkern/entpool.h>
#include <machine/limits.h>
#ifdef __HAVE_CPU_COUNTER
#include <machine/cpu_counter.h>
#endif
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
#define MINENTROPYBYTES ENTROPY_CAPACITY
#define MINENTROPYBITS (MINENTROPYBYTES*NBBY)
#define MINSAMPLES (2*MINENTROPYBITS)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* struct entropy_cpu
*
* Per-CPU entropy state. The pool is allocated separately
* because percpu(9) sometimes moves per-CPU objects around
* without zeroing them, which would lead to unwanted copies of
fix few typos in comments for word "because".
2022-03-05 00:12:03 +03:00
* sensitive secrets. The evcnt is allocated separately because
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
* evcnt(9) assumes it stays put in memory.
*/
struct entropy_cpu {
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
struct entropy_cpu_evcnt {
struct evcnt softint;
struct evcnt intrdrop;
struct evcnt intrtrunc;
} *ec_evcnt;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
struct entpool *ec_pool;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned ec_bitspending;
unsigned ec_samplespending;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
bool ec_locked;
};
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
/*
* struct entropy_cpu_lock
*
* State for locking the per-CPU entropy state.
*/
struct entropy_cpu_lock {
int ecl_s;
uint64_t ecl_ncsw;
};
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* struct rndsource_cpu
*
* Per-CPU rndsource state.
*/
struct rndsource_cpu {
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
unsigned rc_entropybits;
unsigned rc_timesamples;
unsigned rc_datasamples;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
rnd_delta_t rc_timedelta;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
};
/*
* entropy_global (a.k.a. E for short in this file)
*
* Global entropy state. Writes protected by the global lock.
* Some fields, marked (A), can be read outside the lock, and are
* maintained with atomic_load/store_relaxed.
*/
struct {
kmutex_t lock; /* covers all global state */
struct entpool pool; /* global pool for extraction */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitsneeded; /* (A) needed globally */
unsigned bitspending; /* pending in per-CPU pools */
unsigned samplesneeded; /* (A) needed globally */
unsigned samplespending; /* pending in per-CPU pools */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
unsigned timestamp; /* (A) time of last consolidation */
unsigned epoch; /* (A) changes when needed -> 0 */
kcondvar_t cv; /* notifies state changes */
struct selinfo selq; /* notifies needed -> 0 */
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
struct lwp *sourcelock; /* lock on list of sources */
entropy: Use a separate condvar for rndsource list lock. Otherwise, two processes both waiting for entropy will dance around waking each other up (by releasing the rndsource list lock) and going back to sleep (waiting for entropy). Witnessed on the armv7 testbed when /etc/security presumably ran twice over a >day-long test, until the metaphorical plug got pulled: net/if_ipsec/t_ipsec_natt (509/888): 2 test cases ipsecif_natt_transport_null: [ 37123.2631856] entropy: pid 1005 (dd) blocking due to lack of entropy [256.523317s] Failed: atf-check failed; see the output of the test for details ipsecif_natt_transport_rijndaelcbc: [274.370791s] Failed: atf-check failed; see the output of the test for details [532.486697s] ... puffs_lstat_symlink: [ 123442.1606517] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1835067] entropy: pid 1005 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 1005 (dd) blocking due to lack of entropy ...
2021-01-14 02:53:23 +03:00
kcondvar_t sourcelock_cv; /* notifies sourcelock release */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_HEAD(,krndsource) sources; /* list of entropy sources */
bool consolidate; /* kick thread to consolidate */
bool seed_rndsource; /* true if seed source is attached */
bool seeded; /* true if seed file already loaded */
} entropy_global __cacheline_aligned = {
/* Fields that must be initialized when the kernel is loaded. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
.bitsneeded = MINENTROPYBITS,
.samplesneeded = MINSAMPLES,
Print `entropy: ready' only when we first have full entropy. Now that we consolidate entropy in rndctl -L and equivalent, not just when the operator chooses, epoch != -1 no longer necessarily means full entropy -- it just means `time to (re)seed, whether justified by entropy accounting or by explicit consolidation'. There is a bug on x86 systems with RDRAND/RDSEED that prevents this message from appearing at all: it happens so early that consinit has not run yet, so it just goes into oblivion. Need to fix that some other way!
2020-05-07 22:07:29 +03:00
.epoch = (unsigned)-1, /* -1 means entropy never consolidated */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
.sources = LIST_HEAD_INITIALIZER(entropy_global.sources),
};
#define E (&entropy_global) /* declutter */
/* Read-mostly globals */
static struct percpu *entropy_percpu __read_mostly; /* struct entropy_cpu */
static void *entropy_sih __read_mostly; /* softint handler */
static struct lwp *entropy_lwp __read_mostly; /* housekeeping thread */
static struct krndsource seed_rndsource __read_mostly;
/*
* Event counters
*
* Must be careful with adding these because they can serve as
* side channels.
*/
static struct evcnt entropy_discretionary_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "discretionary");
EVCNT_ATTACH_STATIC(entropy_discretionary_evcnt);
static struct evcnt entropy_immediate_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "immediate");
EVCNT_ATTACH_STATIC(entropy_immediate_evcnt);
static struct evcnt entropy_partial_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "partial");
EVCNT_ATTACH_STATIC(entropy_partial_evcnt);
static struct evcnt entropy_consolidate_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "consolidate");
EVCNT_ATTACH_STATIC(entropy_consolidate_evcnt);
static struct evcnt entropy_extract_fail_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "extract fail");
EVCNT_ATTACH_STATIC(entropy_extract_fail_evcnt);
static struct evcnt entropy_request_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "request");
EVCNT_ATTACH_STATIC(entropy_request_evcnt);
static struct evcnt entropy_deplete_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "deplete");
EVCNT_ATTACH_STATIC(entropy_deplete_evcnt);
static struct evcnt entropy_notify_evcnt =
EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "entropy", "notify");
EVCNT_ATTACH_STATIC(entropy_notify_evcnt);
/* Sysctl knobs */
Make variable unused outside kern_entropy.c static.
2020-05-08 18:54:11 +03:00
static bool entropy_collection = 1;
static bool entropy_depletion = 0; /* Silly! */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static const struct sysctlnode *entropy_sysctlroot;
static struct sysctllog *entropy_sysctllog;
/* Forward declarations */
static void entropy_init_cpu(void *, void *, struct cpu_info *);
static void entropy_fini_cpu(void *, void *, struct cpu_info *);
static void entropy_account_cpu(struct entropy_cpu *);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
static void entropy_enter(const void *, size_t, unsigned, bool);
static bool entropy_enter_intr(const void *, size_t, unsigned, bool);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static void entropy_softintr(void *);
static void entropy_thread(void *);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
static bool entropy_pending(void);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static void entropy_pending_cpu(void *, void *, struct cpu_info *);
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
static void entropy_do_consolidate(void);
static void entropy_consolidate_xc(void *, void *);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static void entropy_notify(void);
static int sysctl_entropy_consolidate(SYSCTLFN_ARGS);
New sysctl kern.entropy.gather=1 to trigger entropy gathering. Invokes all on-demand RNG sources. This enables HWRNG driver developers to use a dtrace probe on rnd_add_data to examine the data coming out of the HWRNG: dtrace -n 'fbt::rnd_add_data:entry /args[0]->name == "amdccp0"/ { ...examine buffer args[1] length args[2]... }'
2020-05-05 18:31:42 +03:00
static int sysctl_entropy_gather(SYSCTLFN_ARGS);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static void filt_entropy_read_detach(struct knote *);
static int filt_entropy_read_event(struct knote *, long);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
static int entropy_request(size_t, int);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
static void rnd_add_data_internal(struct krndsource *, const void *,
uint32_t, uint32_t, bool);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static void rnd_add_data_1(struct krndsource *, const void *, uint32_t,
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
uint32_t, bool, uint32_t, bool);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static unsigned rndsource_entropybits(struct krndsource *);
static void rndsource_entropybits_cpu(void *, void *, struct cpu_info *);
static void rndsource_to_user(struct krndsource *, rndsource_t *);
static void rndsource_to_user_est(struct krndsource *, rndsource_est_t *);
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
static void rndsource_to_user_est_cpu(void *, void *, struct cpu_info *);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_timer()
*
* Cycle counter, time counter, or anything that changes a wee bit
* unpredictably.
*/
static inline uint32_t
entropy_timer(void)
{
struct bintime bt;
uint32_t v;
/* If we have a CPU cycle counter, use the low 32 bits. */
#ifdef __HAVE_CPU_COUNTER
if (__predict_true(cpu_hascounter()))
return cpu_counter32();
#endif /* __HAVE_CPU_COUNTER */
/* If we're cold, tough. Can't binuptime while cold. */
if (__predict_false(cold))
return 0;
/* Fold the 128 bits of binuptime into 32 bits. */
binuptime(&bt);
v = bt.frac;
v ^= bt.frac >> 32;
v ^= bt.sec;
v ^= bt.sec >> 32;
return v;
}
static void
attach_seed_rndsource(void)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cpu_intr_p());
KASSERT(!cpu_softintr_p());
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* First called no later than entropy_init, while we are still
* single-threaded, so no need for RUN_ONCE.
*/
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (E->seed_rndsource)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
return;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rnd_attach_source(&seed_rndsource, "seed", RND_TYPE_UNKNOWN,
RND_FLAG_COLLECT_VALUE);
E->seed_rndsource = true;
}
/*
* entropy_init()
*
* Initialize the entropy subsystem. Panic on failure.
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* Requires percpu(9) and sysctl(9) to be initialized. Must run
* while cold.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static void
entropy_init(void)
{
uint32_t extra[2];
struct krndsource *rs;
unsigned i = 0;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Grab some cycle counts early at boot. */
extra[i++] = entropy_timer();
/* Run the entropy pool cryptography self-test. */
if (entpool_selftest() == -1)
panic("entropy pool crypto self-test failed");
/* Create the sysctl directory. */
sysctl_createv(&entropy_sysctllog, 0, NULL, &entropy_sysctlroot,
CTLFLAG_PERMANENT, CTLTYPE_NODE, "entropy",
SYSCTL_DESCR("Entropy (random number sources) options"),
NULL, 0, NULL, 0,
CTL_KERN, CTL_CREATE, CTL_EOL);
/* Create the sysctl knobs. */
/* XXX These shouldn't be writable at securelevel>0. */
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE, CTLTYPE_BOOL, "collection",
SYSCTL_DESCR("Automatically collect entropy from hardware"),
NULL, 0, &entropy_collection, 0, CTL_CREATE, CTL_EOL);
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE, CTLTYPE_BOOL, "depletion",
SYSCTL_DESCR("`Deplete' entropy pool when observed"),
NULL, 0, &entropy_depletion, 0, CTL_CREATE, CTL_EOL);
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE, CTLTYPE_INT, "consolidate",
SYSCTL_DESCR("Trigger entropy consolidation now"),
sysctl_entropy_consolidate, 0, NULL, 0, CTL_CREATE, CTL_EOL);
New sysctl kern.entropy.gather=1 to trigger entropy gathering. Invokes all on-demand RNG sources. This enables HWRNG driver developers to use a dtrace probe on rnd_add_data to examine the data coming out of the HWRNG: dtrace -n 'fbt::rnd_add_data:entry /args[0]->name == "amdccp0"/ { ...examine buffer args[1] length args[2]... }'
2020-05-05 18:31:42 +03:00
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE, CTLTYPE_INT, "gather",
SYSCTL_DESCR("Trigger entropy gathering from sources now"),
sysctl_entropy_gather, 0, NULL, 0, CTL_CREATE, CTL_EOL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* XXX These should maybe not be readable at securelevel>0. */
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READONLY|CTLFLAG_PRIVATE, CTLTYPE_INT,
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
"needed",
SYSCTL_DESCR("Systemwide entropy deficit (bits of entropy)"),
NULL, 0, &E->bitsneeded, 0, CTL_CREATE, CTL_EOL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READONLY|CTLFLAG_PRIVATE, CTLTYPE_INT,
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
"pending",
SYSCTL_DESCR("Number of bits of entropy pending on CPUs"),
NULL, 0, &E->bitspending, 0, CTL_CREATE, CTL_EOL);
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READONLY|CTLFLAG_PRIVATE, CTLTYPE_INT,
"samplesneeded",
SYSCTL_DESCR("Systemwide entropy deficit (samples)"),
NULL, 0, &E->samplesneeded, 0, CTL_CREATE, CTL_EOL);
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READONLY|CTLFLAG_PRIVATE, CTLTYPE_INT,
"samplespending",
SYSCTL_DESCR("Number of samples pending on CPUs"),
NULL, 0, &E->samplespending, 0, CTL_CREATE, CTL_EOL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
sysctl_createv(&entropy_sysctllog, 0, &entropy_sysctlroot, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READONLY|CTLFLAG_PRIVATE, CTLTYPE_INT,
"epoch", SYSCTL_DESCR("Entropy epoch"),
NULL, 0, &E->epoch, 0, CTL_CREATE, CTL_EOL);
/* Initialize the global state for multithreaded operation. */
entropy(9): Reduce global entropy lock from IPL_VM to IPL_SOFTSERIAL. This is no longer ever taken in hard interrupt context, so there's no longer any need to block interrupts while doing crypto operations on the global entropy pool.
2022-03-19 02:35:19 +03:00
mutex_init(&E->lock, MUTEX_DEFAULT, IPL_SOFTSERIAL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
cv_init(&E->cv, "entropy");
selinit(&E->selq);
entropy: Use a separate condvar for rndsource list lock. Otherwise, two processes both waiting for entropy will dance around waking each other up (by releasing the rndsource list lock) and going back to sleep (waiting for entropy). Witnessed on the armv7 testbed when /etc/security presumably ran twice over a >day-long test, until the metaphorical plug got pulled: net/if_ipsec/t_ipsec_natt (509/888): 2 test cases ipsecif_natt_transport_null: [ 37123.2631856] entropy: pid 1005 (dd) blocking due to lack of entropy [256.523317s] Failed: atf-check failed; see the output of the test for details ipsecif_natt_transport_rijndaelcbc: [274.370791s] Failed: atf-check failed; see the output of the test for details [532.486697s] ... puffs_lstat_symlink: [ 123442.1606517] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1835067] entropy: pid 1005 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 1005 (dd) blocking due to lack of entropy ...
2021-01-14 02:53:23 +03:00
cv_init(&E->sourcelock_cv, "entsrclock");
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Make sure the seed source is attached. */
attach_seed_rndsource();
/* Note if the bootloader didn't provide a seed. */
if (!E->seeded)
entropy: Reduce `no seed from bootloader' message to debug level. This does not necessarily indicate a problem -- only x86 and arm pass a seed from the bootloader anyway -- so it makes for an always-on warning on some platforms, including all rump kernels, which is not helpful.
2021-01-21 20:33:55 +03:00
aprint_debug("entropy: no seed from bootloader\n");
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Allocate the per-CPU records for all early entropy sources. */
LIST_FOREACH(rs, &E->sources, list)
rs->state = percpu_alloc(sizeof(struct rndsource_cpu));
entropy(9): Create per-CPU state earlier. This will make it possible to use it from interrupts as soon as they start, which means the global entropy pool lock won't have to block interrupts.
2022-03-19 02:34:44 +03:00
/* Allocate and initialize the per-CPU state. */
entropy_percpu = percpu_create(sizeof(struct entropy_cpu),
entropy_init_cpu, entropy_fini_cpu, NULL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Enter the boot cycle count to get started. */
extra[i++] = entropy_timer();
KASSERT(i == __arraycount(extra));
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter(extra, sizeof extra, /*nbits*/0, /*count*/false);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(extra, 0, sizeof extra);
entropy(9): Use the early-entropy path only while cold. This way, we never take the global entropy lock from interrupt handlers (no interrupts while cold), so the global entropy lock need not block interrupts. There's an annoying ordering issue here: softint_establish doesn't work until after CPUs have been detected, which happens inside configure(), which is also what enables interrupts. So we have no opportunity to softint_establish the entropy softint _before_ interrupts are enabled. To work around this, we have to put a conditional into the interrupt path, and go out of our way to process any queued samples after establishing the softint. If we just made softint_establish work early, like percpu_create does now, this problem would go away and we could delete a bit of logic here. Candidate fix for PR kern/56730.
2022-03-19 02:34:56 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_init_late()
*
* Late initialization. Panic on failure.
*
* Requires CPUs to have been detected and LWPs to have started.
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* Must run while cold.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static void
entropy_init_late(void)
{
int error;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* Establish the softint at the highest softint priority level.
* Must happen after CPU detection.
*/
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
entropy_sih = softint_establish(SOFTINT_SERIAL|SOFTINT_MPSAFE,
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
&entropy_softintr, NULL);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (entropy_sih == NULL)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
panic("unable to establish entropy softint");
/*
* Create the entropy housekeeping thread. Must happen after
* lwpinit.
*/
error = kthread_create(PRI_NONE, KTHREAD_MPSAFE|KTHREAD_TS, NULL,
entropy_thread, NULL, &entropy_lwp, "entbutler");
if (error)
panic("unable to create entropy housekeeping thread: %d",
error);
}
/*
* entropy_init_cpu(ptr, cookie, ci)
*
* percpu(9) constructor for per-CPU entropy pool.
*/
static void
entropy_init_cpu(void *ptr, void *cookie, struct cpu_info *ci)
{
struct entropy_cpu *ec = ptr;
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
const char *cpuname;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
ec->ec_evcnt = kmem_alloc(sizeof(*ec->ec_evcnt), KM_SLEEP);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
ec->ec_pool = kmem_zalloc(sizeof(*ec->ec_pool), KM_SLEEP);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
ec->ec_bitspending = 0;
ec->ec_samplespending = 0;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
ec->ec_locked = false;
entropy(9): Create per-CPU state earlier. This will make it possible to use it from interrupts as soon as they start, which means the global entropy pool lock won't have to block interrupts.
2022-03-19 02:34:44 +03:00
/* XXX ci_cpuname may not be initialized early enough. */
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
cpuname = ci->ci_cpuname[0] == '\0' ? "cpu0" : ci->ci_cpuname;
evcnt_attach_dynamic(&ec->ec_evcnt->softint, EVCNT_TYPE_MISC, NULL,
cpuname, "entropy softint");
evcnt_attach_dynamic(&ec->ec_evcnt->intrdrop, EVCNT_TYPE_MISC, NULL,
cpuname, "entropy intrdrop");
evcnt_attach_dynamic(&ec->ec_evcnt->intrtrunc, EVCNT_TYPE_MISC, NULL,
cpuname, "entropy intrtrunc");
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
* entropy_fini_cpu(ptr, cookie, ci)
*
* percpu(9) destructor for per-CPU entropy pool.
*/
static void
entropy_fini_cpu(void *ptr, void *cookie, struct cpu_info *ci)
{
struct entropy_cpu *ec = ptr;
/*
* Zero any lingering data. Disclosure of the per-CPU pool
* shouldn't retroactively affect the security of any keys
* generated, because entpool(9) erases whatever we have just
* drawn out of any pool, but better safe than sorry.
*/
explicit_memset(ec->ec_pool, 0, sizeof(*ec->ec_pool));
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
evcnt_detach(&ec->ec_evcnt->intrtrunc);
evcnt_detach(&ec->ec_evcnt->intrdrop);
evcnt_detach(&ec->ec_evcnt->softint);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
kmem_free(ec->ec_pool, sizeof(*ec->ec_pool));
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
kmem_free(ec->ec_evcnt, sizeof(*ec->ec_evcnt));
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
/*
* ec = entropy_cpu_get(&lock)
* entropy_cpu_put(&lock, ec)
*
* Lock and unlock the per-CPU entropy state. This only prevents
* access on the same CPU -- by hard interrupts, by soft
* interrupts, or by other threads.
*
* Blocks soft interrupts and preemption altogether; doesn't block
* hard interrupts, but causes samples in hard interrupts to be
* dropped.
*/
static struct entropy_cpu *
entropy_cpu_get(struct entropy_cpu_lock *lock)
{
struct entropy_cpu *ec;
ec = percpu_getref(entropy_percpu);
lock->ecl_s = splsoftserial();
KASSERT(!ec->ec_locked);
ec->ec_locked = true;
lock->ecl_ncsw = curlwp->l_ncsw;
__insn_barrier();
return ec;
}
static void
entropy_cpu_put(struct entropy_cpu_lock *lock, struct entropy_cpu *ec)
{
KASSERT(ec == percpu_getptr_remote(entropy_percpu, curcpu()));
KASSERT(ec->ec_locked);
__insn_barrier();
KASSERT(lock->ecl_ncsw == curlwp->l_ncsw);
ec->ec_locked = false;
splx(lock->ecl_s);
percpu_putref(entropy_percpu);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_seed(seed)
*
* Seed the entropy pool with seed. Meant to be called as early
* as possible by the bootloader; may be called before or after
* entropy_init. Must be called before system reaches userland.
* Must be called in thread or soft interrupt context, not in hard
* interrupt context. Must be called at most once.
*
* Overwrites the seed in place. Caller may then free the memory.
*/
static void
entropy_seed(rndsave_t *seed)
{
SHA1_CTX ctx;
uint8_t digest[SHA1_DIGEST_LENGTH];
bool seeded;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cpu_intr_p());
KASSERT(!cpu_softintr_p());
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* Verify the checksum. If the checksum fails, take the data
* but ignore the entropy estimate -- the file may have been
* incompletely written with garbage, which is harmless to add
* but may not be as unpredictable as alleged.
*/
SHA1Init(&ctx);
SHA1Update(&ctx, (const void *)&seed->entropy, sizeof(seed->entropy));
SHA1Update(&ctx, seed->data, sizeof(seed->data));
SHA1Final(digest, &ctx);
CTASSERT(sizeof(seed->digest) == sizeof(digest));
if (!consttime_memequal(digest, seed->digest, sizeof(digest))) {
printf("entropy: invalid seed checksum\n");
seed->entropy = 0;
}
Accept both byte orders for random seed in the kernel. The file format was defined with a machine-dependent 32-bit integer field (the estimated number of bits of entropy in the process that generated it). Fortunately we have a checksum to verify the order. This way you can use `rndctl -S' on a little-endian machine to generate a seed when installing NetBSD on a big-endian machine, and the kernel will accept it on boot.
2020-04-30 06:42:23 +03:00
explicit_memset(&ctx, 0, sizeof ctx);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(digest, 0, sizeof digest);
Accept both byte orders for random seed in the kernel. The file format was defined with a machine-dependent 32-bit integer field (the estimated number of bits of entropy in the process that generated it). Fortunately we have a checksum to verify the order. This way you can use `rndctl -S' on a little-endian machine to generate a seed when installing NetBSD on a big-endian machine, and the kernel will accept it on boot.
2020-04-30 06:42:23 +03:00
/*
* If the entropy is insensibly large, try byte-swapping.
* Otherwise assume the file is corrupted and act as though it
* has zero entropy.
*/
if (howmany(seed->entropy, NBBY) > sizeof(seed->data)) {
seed->entropy = bswap32(seed->entropy);
if (howmany(seed->entropy, NBBY) > sizeof(seed->data))
seed->entropy = 0;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Make sure the seed source is attached. */
attach_seed_rndsource();
/* Test and set E->seeded. */
seeded = E->seeded;
Don't reject seed file entropy estimates, until one is nonzero. We try to avoid counting the seed file's entropy twice, e.g. once from the boot loader and once from rndctl via /etc/rc.d/random_seed. But previously, if you had a /var/db/entropy-file that was deemed to have zero entropy, that would prevent rndctl -L from _ever_ setting a nonzero entropy estimate, even if you (say) copy a seed file over from another machine (over a non-eavesdroppable medium) and try to load it in with rndctl -L, e.g. via `/etc/rc.d/random_seed start'. Now we accept the first _nonzero_ entropy estimate from a seed file. The operator can still always trick the kernel into believing there's entropy in the system by writing data to /dev/random, if the operator knows something the kernel doesn't; this only affects the _automated_ seed file loading.
2020-05-06 21:31:05 +03:00
E->seeded = (seed->entropy > 0);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* If we've been seeded, may be re-entering the same seed
* (e.g., bootloader vs module init, or something). No harm in
* entering it twice, but it contributes no additional entropy.
*/
if (seeded) {
printf("entropy: double-seeded by bootloader\n");
seed->entropy = 0;
} else {
Don't reject seed file entropy estimates, until one is nonzero. We try to avoid counting the seed file's entropy twice, e.g. once from the boot loader and once from rndctl via /etc/rc.d/random_seed. But previously, if you had a /var/db/entropy-file that was deemed to have zero entropy, that would prevent rndctl -L from _ever_ setting a nonzero entropy estimate, even if you (say) copy a seed file over from another machine (over a non-eavesdroppable medium) and try to load it in with rndctl -L, e.g. via `/etc/rc.d/random_seed start'. Now we accept the first _nonzero_ entropy estimate from a seed file. The operator can still always trick the kernel into believing there's entropy in the system by writing data to /dev/random, if the operator knows something the kernel doesn't; this only affects the _automated_ seed file loading.
2020-05-06 21:31:05 +03:00
printf("entropy: entering seed from bootloader"
" with %u bits of entropy\n", (unsigned)seed->entropy);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/* Enter it into the pool and promptly zero it. */
rnd_add_data(&seed_rndsource, seed->data, sizeof(seed->data),
seed->entropy);
explicit_memset(seed, 0, sizeof(*seed));
}
/*
* entropy_bootrequest()
*
* Request entropy from all sources at boot, once config is
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* complete and interrupts are running but we are still cold.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
void
entropy_bootrequest(void)
{
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
int error;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cpu_intr_p());
KASSERT(!cpu_softintr_p());
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* Request enough to satisfy the maximum entropy shortage.
* This is harmless overkill if the bootloader provided a seed.
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
error = entropy_request(MINENTROPYBYTES, ENTROPY_WAIT);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERTMSG(error == 0, "error=%d", error);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
* entropy_epoch()
*
* Returns the current entropy epoch. If this changes, you should
Print `entropy: ready' only when we first have full entropy. Now that we consolidate entropy in rndctl -L and equivalent, not just when the operator chooses, epoch != -1 no longer necessarily means full entropy -- it just means `time to (re)seed, whether justified by entropy accounting or by explicit consolidation'. There is a bug on x86 systems with RDRAND/RDSEED that prevents this message from appearing at all: it happens so early that consinit has not run yet, so it just goes into oblivion. Need to fix that some other way!
2020-05-07 22:07:29 +03:00
* reseed. If -1, means system entropy has not yet reached full
* entropy or been explicitly consolidated; never reverts back to
* -1. Never zero, so you can always use zero as an uninitialized
* sentinel value meaning `reseed ASAP'.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Usage model:
*
* struct foo {
* struct crypto_prng prng;
* unsigned epoch;
* } *foo;
*
* unsigned epoch = entropy_epoch();
* if (__predict_false(epoch != foo->epoch)) {
* uint8_t seed[32];
* if (entropy_extract(seed, sizeof seed, 0) != 0)
* warn("no entropy");
* crypto_prng_reseed(&foo->prng, seed, sizeof seed);
* foo->epoch = epoch;
* }
*/
unsigned
entropy_epoch(void)
{
/*
* Unsigned int, so no need for seqlock for an atomic read, but
* make sure we read it afresh each time.
*/
return atomic_load_relaxed(&E->epoch);
}
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
/*
* entropy_ready()
*
* True if the entropy pool has full entropy.
*/
bool
entropy_ready(void)
{
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
return atomic_load_relaxed(&E->bitsneeded) == 0;
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_account_cpu(ec)
*
* Consider whether to consolidate entropy into the global pool
* after we just added some into the current CPU's pending pool.
*
* - If this CPU can provide enough entropy now, do so.
*
* - If this and whatever else is available on other CPUs can
* provide enough entropy, kick the consolidation thread.
*
* - Otherwise, do as little as possible, except maybe consolidate
* entropy at most once a minute.
*
* Caller must be bound to a CPU and therefore have exclusive
* access to ec. Will acquire and release the global lock.
*/
static void
entropy_account_cpu(struct entropy_cpu *ec)
{
entropy(9): Lock the per-CPU state in entropy_account_cpu. This was previously called with the per-CPU state locked, which worked fine as long as the global entropy lock was a spin lock so acquiring it would never sleep. Now it's an adaptive lock, so it's not safe to take with the per-CPU state lock -- but we still need to prevent reentrant access to the per-CPU entropy pool by interrupt handlers while we're extracting from it. So now the logic for entering a sample is: - lock per-CPU state - entpool_enter - unlock per-CPU state - if anything pending on this CPU and it's time to consolidate: - lock global entropy state - lock per-CPU state - transfer - unlock per-CPU state - unlock global entropy state
2022-03-20 16:17:32 +03:00
struct entropy_cpu_lock lock;
struct entropy_cpu *ec0;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitsdiff, samplesdiff;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cpu_intr_p());
KASSERT(!cold);
entropy(9): Bind to CPU temporarily to avoid race with lwp migration. More fallout from the IPL_VM->IPL_SOFTSERIAL change. In entropy_enter, there is a window when the lwp can be migrated to another CPU: ec = entropy_cpu_get(); ... pending = ec->ec_pending + ...; ... entropy_cpu_put(); /* lwp migration possible here */ if (pending) entropy_account_cpu(ec); If this happens, we may trip over any of several problems in entropy_account_cpu because it assumes ec is the current CPU's state in order to decide whether we have anything to contribute from the local pool to the global pool. No need to do this in entropy_softintr because softints are bound to the CPU anyway.
2022-03-24 02:18:17 +03:00
KASSERT(curlwp->l_pflag & LP_BOUND);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* If there's no entropy needed, and entropy has been
* consolidated in the last minute, do nothing.
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (__predict_true(atomic_load_relaxed(&E->bitsneeded) == 0) &&
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
__predict_true(!atomic_load_relaxed(&entropy_depletion)) &&
__predict_true((time_uptime - E->timestamp) <= 60))
return;
entropy(9): Lock the per-CPU state in entropy_account_cpu. This was previously called with the per-CPU state locked, which worked fine as long as the global entropy lock was a spin lock so acquiring it would never sleep. Now it's an adaptive lock, so it's not safe to take with the per-CPU state lock -- but we still need to prevent reentrant access to the per-CPU entropy pool by interrupt handlers while we're extracting from it. So now the logic for entering a sample is: - lock per-CPU state - entpool_enter - unlock per-CPU state - if anything pending on this CPU and it's time to consolidate: - lock global entropy state - lock per-CPU state - transfer - unlock per-CPU state - unlock global entropy state
2022-03-20 16:17:32 +03:00
/*
* Consider consolidation, under the global lock and with the
* per-CPU state locked.
*/
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
entropy(9): Lock the per-CPU state in entropy_account_cpu. This was previously called with the per-CPU state locked, which worked fine as long as the global entropy lock was a spin lock so acquiring it would never sleep. Now it's an adaptive lock, so it's not safe to take with the per-CPU state lock -- but we still need to prevent reentrant access to the per-CPU entropy pool by interrupt handlers while we're extracting from it. So now the logic for entering a sample is: - lock per-CPU state - entpool_enter - unlock per-CPU state - if anything pending on this CPU and it's time to consolidate: - lock global entropy state - lock per-CPU state - transfer - unlock per-CPU state - unlock global entropy state
2022-03-20 16:17:32 +03:00
ec0 = entropy_cpu_get(&lock);
KASSERT(ec0 == ec);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (ec->ec_bitspending == 0 && ec->ec_samplespending == 0) {
entropy(9): Fix another new race in entropy_account_cpu. The consolidation xcall can preempt entropy_enter, between when it unlocks the per-CPU state and when it calls entropy_account_cpu, with the effect of setting ec->ec_pending=0. Previously this was impossible because we called entropy_account_cpu with the per-CPU state still locked, but that doesn't work now that the global entropy lock is an adaptive lock which might sleep which is forbidden while the per-CPU state is locked.
2022-03-20 16:18:11 +03:00
/* Raced with consolidation xcall. Nothing to do. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
} else if (E->bitsneeded != 0 && E->bitsneeded <= ec->ec_bitspending) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* If we have not yet attained full entropy but we can
* now, do so. This way we disseminate entropy
* promptly when it becomes available early at boot;
* otherwise we leave it to the entropy consolidation
* thread, which is rate-limited to mitigate side
* channels and abuse.
*/
uint8_t buf[ENTPOOL_CAPACITY];
/* Transfer from the local pool to the global pool. */
entpool_extract(ec->ec_pool, buf, sizeof buf);
entpool_enter(&E->pool, buf, sizeof buf);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
atomic_store_relaxed(&ec->ec_bitspending, 0);
atomic_store_relaxed(&ec->ec_samplespending, 0);
atomic_store_relaxed(&E->bitsneeded, 0);
atomic_store_relaxed(&E->samplesneeded, 0);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Notify waiters that we now have full entropy. */
entropy_notify();
entropy_immediate_evcnt.ev_count++;
Prune dead branch.
2020-05-09 09:12:32 +03:00
} else {
entropy(9): Shuffle some assertions around. Tripped over (diff || E->pending == ENTROPY_CAPACITY*NBBY), not sure why yet, printing values will help. No functional change intended.
2022-03-20 16:17:44 +03:00
/* Determine how much we can add to the global pool. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
KASSERTMSG(E->bitspending <= MINENTROPYBITS,
"E->bitspending=%u", E->bitspending);
bitsdiff = MIN(ec->ec_bitspending,
MINENTROPYBITS - E->bitspending);
KASSERTMSG(E->samplespending <= MINSAMPLES,
"E->samplespending=%u", E->samplespending);
samplesdiff = MIN(ec->ec_samplespending,
MINSAMPLES - E->samplespending);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Shuffle some assertions around. Tripped over (diff || E->pending == ENTROPY_CAPACITY*NBBY), not sure why yet, printing values will help. No functional change intended.
2022-03-20 16:17:44 +03:00
* This should make a difference unless we are already
* saturated.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
KASSERTMSG((bitsdiff || samplesdiff ||
E->bitspending == MINENTROPYBITS ||
E->samplespending == MINSAMPLES),
"bitsdiff=%u E->bitspending=%u ec->ec_bitspending=%u"
"samplesdiff=%u E->samplespending=%u"
" ec->ec_samplespending=%u"
" minentropybits=%u minsamples=%u",
bitsdiff, E->bitspending, ec->ec_bitspending,
samplesdiff, E->samplespending, ec->ec_samplespending,
(unsigned)MINENTROPYBITS, (unsigned)MINSAMPLES);
entropy(9): Shuffle some assertions around. Tripped over (diff || E->pending == ENTROPY_CAPACITY*NBBY), not sure why yet, printing values will help. No functional change intended.
2022-03-20 16:17:44 +03:00
/* Add to the global, subtract from the local. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
E->bitspending += bitsdiff;
KASSERTMSG(E->bitspending <= MINENTROPYBITS,
"E->bitspending=%u", E->bitspending);
atomic_store_relaxed(&ec->ec_bitspending,
ec->ec_bitspending - bitsdiff);
E->samplespending += samplesdiff;
KASSERTMSG(E->samplespending <= MINSAMPLES,
"E->samplespending=%u", E->samplespending);
atomic_store_relaxed(&ec->ec_samplespending,
ec->ec_samplespending - samplesdiff);
/* One or the other must have gone up from zero. */
KASSERT(E->bitspending || E->samplespending);
if (E->bitsneeded <= E->bitspending ||
E->samplesneeded <= E->samplespending) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* Enough bits or at least samples between all
* the per-CPU pools. Leave a note for the
* housekeeping thread to consolidate entropy
* next time it wakes up -- and wake it up if
* this is the first time, to speed things up.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* If we don't need any entropy, this doesn't
* mean much, but it is the only time we ever
* gather additional entropy in case the
* accounting has been overly optimistic. This
* happens at most once a minute, so there's
* negligible performance cost.
*/
E->consolidate = true;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->epoch == (unsigned)-1)
cv_broadcast(&E->cv);
if (E->bitsneeded == 0)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_discretionary_evcnt.ev_count++;
} else {
/* Can't get full entropy. Keep gathering. */
entropy_partial_evcnt.ev_count++;
}
}
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy(9): Lock the per-CPU state in entropy_account_cpu. This was previously called with the per-CPU state locked, which worked fine as long as the global entropy lock was a spin lock so acquiring it would never sleep. Now it's an adaptive lock, so it's not safe to take with the per-CPU state lock -- but we still need to prevent reentrant access to the per-CPU entropy pool by interrupt handlers while we're extracting from it. So now the logic for entering a sample is: - lock per-CPU state - entpool_enter - unlock per-CPU state - if anything pending on this CPU and it's time to consolidate: - lock global entropy state - lock per-CPU state - transfer - unlock per-CPU state - unlock global entropy state
2022-03-20 16:17:32 +03:00
entropy_cpu_put(&lock, ec);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
}
/*
* entropy_enter_early(buf, len, nbits)
*
* Do entropy bookkeeping globally, before we have established
* per-CPU pools. Enter directly into the global pool in the hope
* that we enter enough before the first entropy_extract to thwart
* iterative-guessing attacks; entropy_extract will warn if not.
*/
static void
entropy_enter_early(const void *buf, size_t len, unsigned nbits)
{
bool notify = false;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
int s;
KASSERT(cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* We're early at boot before multithreading and multi-CPU
* operation, and we don't have softints yet to defer
* processing from interrupt context, so we have to enter the
* samples directly into the global pool. But interrupts may
* be enabled, and we enter this path from interrupt context,
* so block interrupts until we're done.
*/
s = splhigh();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Enter it into the pool. */
entpool_enter(&E->pool, buf, len);
/*
* Decide whether to notify reseed -- we will do so if either:
* (a) we transition from partial entropy to full entropy, or
* (b) we get a batch of full entropy all at once.
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* We don't count timing samples because we assume, while cold,
* there's not likely to be much jitter yet.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
notify |= (E->bitsneeded && E->bitsneeded <= nbits);
notify |= (nbits >= MINENTROPYBITS);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
/*
* Subtract from the needed count and notify if appropriate.
* We don't count samples here because entropy_timer might
* still be returning zero at this point if there's no CPU
* cycle counter.
*/
E->bitsneeded -= MIN(E->bitsneeded, nbits);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
if (notify) {
entropy_notify();
entropy_immediate_evcnt.ev_count++;
}
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
splx(s);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* entropy_enter(buf, len, nbits, count)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Enter len bytes of data from buf into the system's entropy
* pool, stirring as necessary when the internal buffer fills up.
* nbits is a lower bound on the number of bits of entropy in the
* process that led to this sample.
*/
static void
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter(const void *buf, size_t len, unsigned nbits, bool count)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
struct entropy_cpu_lock lock;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
struct entropy_cpu *ec;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitspending, samplespending;
entropy(9): Bind to CPU temporarily to avoid race with lwp migration. More fallout from the IPL_VM->IPL_SOFTSERIAL change. In entropy_enter, there is a window when the lwp can be migrated to another CPU: ec = entropy_cpu_get(); ... pending = ec->ec_pending + ...; ... entropy_cpu_put(); /* lwp migration possible here */ if (pending) entropy_account_cpu(ec); If this happens, we may trip over any of several problems in entropy_account_cpu because it assumes ec is the current CPU's state in order to decide whether we have anything to contribute from the local pool to the global pool. No need to do this in entropy_softintr because softints are bound to the CPU anyway.
2022-03-24 02:18:17 +03:00
int bound;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
Eliminate curcpu_available() hack. The entropy subsystem is no longer used before curcpu() and curlwp are available on x86.
2020-05-08 03:54:44 +03:00
KASSERTMSG(!cpu_intr_p(),
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
"use entropy_enter_intr from interrupt context");
KASSERTMSG(howmany(nbits, NBBY) <= len,
"impossible entropy rate: %u bits in %zu-byte string", nbits, len);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* If we're still cold, just use entropy_enter_early to put
* samples directly into the global pool.
*/
if (__predict_false(cold)) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_enter_early(buf, len, nbits);
return;
}
entropy(9): Bind to CPU temporarily to avoid race with lwp migration. More fallout from the IPL_VM->IPL_SOFTSERIAL change. In entropy_enter, there is a window when the lwp can be migrated to another CPU: ec = entropy_cpu_get(); ... pending = ec->ec_pending + ...; ... entropy_cpu_put(); /* lwp migration possible here */ if (pending) entropy_account_cpu(ec); If this happens, we may trip over any of several problems in entropy_account_cpu because it assumes ec is the current CPU's state in order to decide whether we have anything to contribute from the local pool to the global pool. No need to do this in entropy_softintr because softints are bound to the CPU anyway.
2022-03-24 02:18:17 +03:00
/*
* Bind ourselves to the current CPU so we don't switch CPUs
* between entering data into the current CPU's pool (and
* updating the pending count) and transferring it to the
* global pool in entropy_account_cpu.
*/
bound = curlwp_bind();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
* With the per-CPU state locked, enter into the per-CPU pool
* and count up what we can add.
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
*
* We don't count samples while cold because entropy_timer
* might still be returning zero if there's no CPU cycle
* counter.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
ec = entropy_cpu_get(&lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entpool_enter(ec->ec_pool, buf, len);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bitspending = ec->ec_bitspending;
bitspending += MIN(MINENTROPYBITS - bitspending, nbits);
atomic_store_relaxed(&ec->ec_bitspending, bitspending);
samplespending = ec->ec_samplespending;
if (__predict_true(count)) {
samplespending += MIN(MINSAMPLES - samplespending, 1);
atomic_store_relaxed(&ec->ec_samplespending, samplespending);
}
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
entropy_cpu_put(&lock, ec);
entropy(9): Avoid reentrance to per-CPU state from sleeping on lock. Changing the global entropy lock from IPL_VM to IPL_SOFTSERIAL meant it went from being a spin lock, which blocks preemption, to being an adaptive lock, which might sleep -- and allow other threads to run concurrently with the softint, even if those threads have softints blocked with splsoftserial. This manifested as KASSERT(!ec->ec_locked) triggering in entropy_consolidate_xc -- presumably entropy_softintr slept on the global entropy lock while holding the per-CPU state locked with ec->ec_locked, and then entropy_consolidate_xc ran. Instead, to protect access to the per-CPU state without taking a global lock, defer entropy_account_cpu until after ec->ec_locked is cleared. This way, we never sleep while holding ec->ec_locked, nor do we incur any contention on shared memory when entering entropy unless we're about to distribute it. To verify this, sprinkle in assertions that curlwp->l_ncsw hasn't changed by the time we release ec->ec_locked.
2022-03-20 03:19:11 +03:00
/* Consolidate globally if appropriate based on what we added. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (bitspending > 0 || samplespending >= MINSAMPLES)
entropy(9): Avoid reentrance to per-CPU state from sleeping on lock. Changing the global entropy lock from IPL_VM to IPL_SOFTSERIAL meant it went from being a spin lock, which blocks preemption, to being an adaptive lock, which might sleep -- and allow other threads to run concurrently with the softint, even if those threads have softints blocked with splsoftserial. This manifested as KASSERT(!ec->ec_locked) triggering in entropy_consolidate_xc -- presumably entropy_softintr slept on the global entropy lock while holding the per-CPU state locked with ec->ec_locked, and then entropy_consolidate_xc ran. Instead, to protect access to the per-CPU state without taking a global lock, defer entropy_account_cpu until after ec->ec_locked is cleared. This way, we never sleep while holding ec->ec_locked, nor do we incur any contention on shared memory when entering entropy unless we're about to distribute it. To verify this, sprinkle in assertions that curlwp->l_ncsw hasn't changed by the time we release ec->ec_locked.
2022-03-20 03:19:11 +03:00
entropy_account_cpu(ec);
entropy(9): Bind to CPU temporarily to avoid race with lwp migration. More fallout from the IPL_VM->IPL_SOFTSERIAL change. In entropy_enter, there is a window when the lwp can be migrated to another CPU: ec = entropy_cpu_get(); ... pending = ec->ec_pending + ...; ... entropy_cpu_put(); /* lwp migration possible here */ if (pending) entropy_account_cpu(ec); If this happens, we may trip over any of several problems in entropy_account_cpu because it assumes ec is the current CPU's state in order to decide whether we have anything to contribute from the local pool to the global pool. No need to do this in entropy_softintr because softints are bound to the CPU anyway.
2022-03-24 02:18:17 +03:00
curlwp_bindx(bound);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* entropy_enter_intr(buf, len, nbits, count)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Enter up to len bytes of data from buf into the system's
* entropy pool without stirring. nbits is a lower bound on the
* number of bits of entropy in the process that led to this
* sample. If the sample could be entered completely, assume
* nbits of entropy pending; otherwise assume none, since we don't
* know whether some parts of the sample are constant, for
* instance. Schedule a softint to stir the entropy pool if
* needed. Return true if used fully, false if truncated at all.
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* Using this in thread or softint context with no spin locks held
* will work, but you might as well use entropy_enter in that
* case.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static bool
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter_intr(const void *buf, size_t len, unsigned nbits, bool count)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
struct entropy_cpu *ec;
bool fullyused = false;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
uint32_t bitspending, samplespending;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
int s;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KASSERTMSG(howmany(nbits, NBBY) <= len,
"impossible entropy rate: %u bits in %zu-byte string", nbits, len);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* If we're still cold, just use entropy_enter_early to put
* samples directly into the global pool.
*/
if (__predict_false(cold)) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_enter_early(buf, len, nbits);
return true;
}
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* In case we were called in thread or interrupt context with
* interrupts unblocked, block soft interrupts up to
* IPL_SOFTSERIAL. This way logic that is safe in interrupt
* context or under a spin lock is also safe in less
* restrictive contexts.
*/
s = splsoftserial();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* Acquire the per-CPU state. If someone is in the middle of
* using it, drop the sample. Otherwise, take the lock so that
* higher-priority interrupts will drop their samples.
*/
ec = percpu_getref(entropy_percpu);
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
if (ec->ec_locked) {
ec->ec_evcnt->intrdrop.ev_count++;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
goto out0;
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
ec->ec_locked = true;
__insn_barrier();
/*
* Enter as much as we can into the per-CPU pool. If it was
* truncated, schedule a softint to stir the pool and stop.
*/
if (!entpool_enter_nostir(ec->ec_pool, buf, len)) {
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
softint_schedule(entropy_sih);
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
ec->ec_evcnt->intrtrunc.ev_count++;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
goto out1;
}
fullyused = true;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
/*
* Count up what we can contribute.
*
* We don't count samples while cold because entropy_timer
* might still be returning zero if there's no CPU cycle
* counter.
*/
bitspending = ec->ec_bitspending;
bitspending += MIN(MINENTROPYBITS - bitspending, nbits);
atomic_store_relaxed(&ec->ec_bitspending, bitspending);
if (__predict_true(count)) {
samplespending = ec->ec_samplespending;
samplespending += MIN(MINSAMPLES - samplespending, 1);
atomic_store_relaxed(&ec->ec_samplespending, samplespending);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Schedule a softint if we added anything and it matters. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (__predict_false(atomic_load_relaxed(&E->bitsneeded) ||
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
atomic_load_relaxed(&entropy_depletion)) &&
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
(nbits != 0 || count) &&
__predict_true(!cold))
softint_schedule(entropy_sih);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
out1: /* Release the per-CPU state. */
KASSERT(ec->ec_locked);
__insn_barrier();
ec->ec_locked = false;
out0: percpu_putref(entropy_percpu);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
splx(s);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
return fullyused;
}
/*
* entropy_softintr(cookie)
*
* Soft interrupt handler for entering entropy. Takes care of
* stirring the local CPU's entropy pool if it filled up during
* hard interrupts, and promptly crediting entropy from the local
* CPU's entropy pool to the global entropy pool if needed.
*/
static void
entropy_softintr(void *cookie)
{
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
struct entropy_cpu_lock lock;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
struct entropy_cpu *ec;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitspending, samplespending;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
* With the per-CPU state locked, stir the pool if necessary
* and determine if there's any pending entropy on this CPU to
* account globally.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
ec = entropy_cpu_get(&lock);
entropy(9): Count dropped or truncated interrupt samples.
2022-03-19 02:35:28 +03:00
ec->ec_evcnt->softint.ev_count++;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entpool_stir(ec->ec_pool);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bitspending = ec->ec_bitspending;
samplespending = ec->ec_samplespending;
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
entropy_cpu_put(&lock, ec);
entropy(9): Avoid reentrance to per-CPU state from sleeping on lock. Changing the global entropy lock from IPL_VM to IPL_SOFTSERIAL meant it went from being a spin lock, which blocks preemption, to being an adaptive lock, which might sleep -- and allow other threads to run concurrently with the softint, even if those threads have softints blocked with splsoftserial. This manifested as KASSERT(!ec->ec_locked) triggering in entropy_consolidate_xc -- presumably entropy_softintr slept on the global entropy lock while holding the per-CPU state locked with ec->ec_locked, and then entropy_consolidate_xc ran. Instead, to protect access to the per-CPU state without taking a global lock, defer entropy_account_cpu until after ec->ec_locked is cleared. This way, we never sleep while holding ec->ec_locked, nor do we incur any contention on shared memory when entering entropy unless we're about to distribute it. To verify this, sprinkle in assertions that curlwp->l_ncsw hasn't changed by the time we release ec->ec_locked.
2022-03-20 03:19:11 +03:00
/* Consolidate globally if appropriate based on what we added. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (bitspending > 0 || samplespending >= MINSAMPLES)
entropy(9): Avoid reentrance to per-CPU state from sleeping on lock. Changing the global entropy lock from IPL_VM to IPL_SOFTSERIAL meant it went from being a spin lock, which blocks preemption, to being an adaptive lock, which might sleep -- and allow other threads to run concurrently with the softint, even if those threads have softints blocked with splsoftserial. This manifested as KASSERT(!ec->ec_locked) triggering in entropy_consolidate_xc -- presumably entropy_softintr slept on the global entropy lock while holding the per-CPU state locked with ec->ec_locked, and then entropy_consolidate_xc ran. Instead, to protect access to the per-CPU state without taking a global lock, defer entropy_account_cpu until after ec->ec_locked is cleared. This way, we never sleep while holding ec->ec_locked, nor do we incur any contention on shared memory when entering entropy unless we're about to distribute it. To verify this, sprinkle in assertions that curlwp->l_ncsw hasn't changed by the time we release ec->ec_locked.
2022-03-20 03:19:11 +03:00
entropy_account_cpu(ec);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
* entropy_thread(cookie)
*
* Handle any asynchronous entropy housekeeping.
*/
static void
entropy_thread(void *cookie)
{
Avoid calling entropy_pending() with E->lock held. This is part I of avoiding percpu_foreach with spin lock held.
2020-04-30 19:43:12 +03:00
bool consolidate;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
for (;;) {
/*
Avoid calling entropy_pending() with E->lock held. This is part I of avoiding percpu_foreach with spin lock held.
2020-04-30 19:43:12 +03:00
* Wait until there's full entropy somewhere among the
* CPUs, as confirmed at most once per minute, or
* someone wants to consolidate.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (entropy_pending()) {
Avoid calling entropy_pending() with E->lock held. This is part I of avoiding percpu_foreach with spin lock held.
2020-04-30 19:43:12 +03:00
consolidate = true;
} else {
mutex_enter(&E->lock);
if (!E->consolidate)
cv_timedwait(&E->cv, &E->lock, 60*hz);
consolidate = E->consolidate;
E->consolidate = false;
mutex_exit(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
Avoid calling entropy_pending() with E->lock held. This is part I of avoiding percpu_foreach with spin lock held.
2020-04-30 19:43:12 +03:00
if (consolidate) {
/* Do it. */
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
entropy_do_consolidate();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
Avoid calling entropy_pending() with E->lock held. This is part I of avoiding percpu_foreach with spin lock held.
2020-04-30 19:43:12 +03:00
/* Mitigate abuse. */
kpause("entropy", false, hz, NULL);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
}
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
struct entropy_pending_count {
uint32_t bitspending;
uint32_t samplespending;
};
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_pending()
*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* True if enough bits or samples are pending on other CPUs to
* warrant consolidation.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
static bool
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_pending(void)
{
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
struct entropy_pending_count count = { 0, 0 }, *C = &count;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
percpu_foreach(entropy_percpu, &entropy_pending_cpu, C);
return C->bitspending >= MINENTROPYBITS ||
C->samplespending >= MINSAMPLES;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
static void
entropy_pending_cpu(void *ptr, void *cookie, struct cpu_info *ci)
{
struct entropy_cpu *ec = ptr;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
struct entropy_pending_count *C = cookie;
uint32_t cpu_bitspending;
uint32_t cpu_samplespending;
cpu_bitspending = atomic_load_relaxed(&ec->ec_bitspending);
cpu_samplespending = atomic_load_relaxed(&ec->ec_samplespending);
C->bitspending += MIN(MINENTROPYBITS - C->bitspending,
cpu_bitspending);
C->samplespending += MIN(MINSAMPLES - C->samplespending,
cpu_samplespending);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
* entropy_do_consolidate()
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Issue a cross-call to gather entropy on all CPUs and advance
* the entropy epoch.
*/
static void
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
entropy_do_consolidate(void)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
static const struct timeval interval = {.tv_sec = 60, .tv_usec = 0};
static struct timeval lasttime; /* serialized by E->lock */
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
struct entpool pool;
uint8_t buf[ENTPOOL_CAPACITY];
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitsdiff, samplesdiff;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
uint64_t ticket;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
ASSERT_SLEEPABLE();
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
/* Gather entropy on all CPUs into a temporary pool. */
memset(&pool, 0, sizeof pool);
ticket = xc_broadcast(0, &entropy_consolidate_xc, &pool, NULL);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
xc_wait(ticket);
/* Acquire the lock to notify waiters. */
mutex_enter(&E->lock);
/* Count another consolidation. */
entropy_consolidate_evcnt.ev_count++;
/* Note when we last consolidated, i.e. now. */
E->timestamp = time_uptime;
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
/* Mix what we gathered into the global pool. */
entpool_extract(&pool, buf, sizeof buf);
entpool_enter(&E->pool, buf, sizeof buf);
explicit_memset(&pool, 0, sizeof pool);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Count the entropy that was gathered. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bitsdiff = MIN(E->bitsneeded, E->bitspending);
atomic_store_relaxed(&E->bitsneeded, E->bitsneeded - bitsdiff);
E->bitspending -= bitsdiff;
if (__predict_false(E->bitsneeded > 0) && bitsdiff != 0) {
entropy(9): Improve entropy warning messages and documentation. - For the main warning message, use less jargon, say `security', and cite the entropy(7) man page for further reading. Document this in rnd(4) and entropy(7). - For the debug-only warning message, say `entropy' only once and omit it from the rnd(4) man page -- it's not very important unless you're debugging the kernel in which case you probably know what you're doing enough to not need the text explained in the man page.
2022-03-20 21:19:57 +03:00
if ((boothowto & AB_DEBUG) != 0 &&
ratecheck(&lasttime, &interval)) {
printf("WARNING:"
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
" consolidating less than full entropy\n");
entropy: Only print consolidation warning of AB_DEBUG. The previous fix for PR kern/55458 changed printf to log(LOG_DEBUG, ...) with the intent of hiding the message unless 'boot -x'. But this did not actually suppress the message to console as log(LOG_DEBUG, ...) will print to console if syslogd is not running yet. So instead, just check for AB_DEBUG flag directly in boothowto, and only printf the message if it is set.
2021-02-12 22:48:26 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
samplesdiff = MIN(E->samplesneeded, E->samplespending);
atomic_store_relaxed(&E->samplesneeded,
E->samplesneeded - samplesdiff);
E->samplespending -= samplesdiff;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Advance the epoch and notify waiters. */
entropy_notify();
/* Release the lock. */
mutex_exit(&E->lock);
}
/*
Fix comments.
2020-05-10 04:29:40 +03:00
* entropy_consolidate_xc(vpool, arg2)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Extract output from the local CPU's input pool and enter it
Fix comments.
2020-05-10 04:29:40 +03:00
* into a temporary pool passed as vpool.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static void
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
entropy_consolidate_xc(void *vpool, void *arg2 __unused)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
struct entpool *pool = vpool;
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
struct entropy_cpu_lock lock;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
struct entropy_cpu *ec;
uint8_t buf[ENTPOOL_CAPACITY];
uint32_t extra[7];
unsigned i = 0;
/* Grab CPU number and cycle counter to mix extra into the pool. */
extra[i++] = cpu_number();
extra[i++] = entropy_timer();
/*
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
* With the per-CPU state locked, extract from the per-CPU pool
* and count it as no longer pending.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
ec = entropy_cpu_get(&lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
extra[i++] = entropy_timer();
entpool_extract(ec->ec_pool, buf, sizeof buf);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
atomic_store_relaxed(&ec->ec_bitspending, 0);
atomic_store_relaxed(&ec->ec_samplespending, 0);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
extra[i++] = entropy_timer();
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
entropy_cpu_put(&lock, ec);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
extra[i++] = entropy_timer();
/*
* Copy over statistics, and enter the per-CPU extract and the
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
* extra timing into the temporary pool, under the global lock.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
mutex_enter(&E->lock);
extra[i++] = entropy_timer();
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
entpool_enter(pool, buf, sizeof buf);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(buf, 0, sizeof buf);
extra[i++] = entropy_timer();
KASSERT(i == __arraycount(extra));
Use a temporary pool to consolidate entropy atomically. There was a low-probability race with the entropy consolidation logic: calls to entropy_extract at the same time as consolidation is happening might witness partial contributions from the CPUs when needed=256, say 64 bits at a time. To avoid this, feed everything from the per-CPU pools into a temporary pool, and then feed the temporary pool into the global pool under the lock at the same time as we update needed.
2020-05-10 03:08:12 +03:00
entpool_enter(pool, extra, sizeof extra);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(extra, 0, sizeof extra);
mutex_exit(&E->lock);
}
/*
* entropy_notify()
*
* Caller just contributed entropy to the global pool. Advance
* the entropy epoch and notify waiters.
*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* Caller must hold the global entropy lock.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static void
entropy_notify(void)
{
Fix two mistakes in entropy accounting. 1. When consolidating entropy from per-CPU pools, drop the amount pending to zero; otherwise the entropy consolidation thread might keep consolidating every second. This uncovered a feedback loop with kern.entropy.depletion=1 and on-demand entropy sources, which is that depleting the pool and then requesting more from it causes the on-demand entropy sources to trigger reseed, which causes cprng_fast/strong to request more which depletes the pool again which causes on-demand entropy sources to trigger reseed, and so on. To work around this: 2. Set a rate limit on reseeding (advancing the entropy epoch) when kern.entropy.depletion=1; otherwise reseeding gets into a feedback loop when there are on-demand entropy sources like RDRAND/RDSEED. (By default, kern.entropy.depletion=0, so this mainly only affects systems where you're simulating what happens when /dev/random blocks for testing.)
2020-05-07 03:55:13 +03:00
static const struct timeval interval = {.tv_sec = 60, .tv_usec = 0};
static struct timeval lasttime; /* serialized by E->lock */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
static bool ready = false, besteffort = false;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
unsigned epoch;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(__predict_false(cold) || mutex_owned(&E->lock));
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* If this is the first time, print a message to the console
* that we're ready so operators can compare it to the timing
* of other events.
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
*
* If we didn't get full entropy from reliable sources, report
* instead that we are running on fumes with best effort. (If
* we ever do get full entropy after that, print the ready
* message once.)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (__predict_false(!ready)) {
if (E->bitsneeded == 0) {
printf("entropy: ready\n");
ready = true;
} else if (E->samplesneeded == 0 && !besteffort) {
printf("entropy: best effort\n");
besteffort = true;
}
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Set the epoch; roll over from UINTMAX-1 to 1. */
Fix two mistakes in entropy accounting. 1. When consolidating entropy from per-CPU pools, drop the amount pending to zero; otherwise the entropy consolidation thread might keep consolidating every second. This uncovered a feedback loop with kern.entropy.depletion=1 and on-demand entropy sources, which is that depleting the pool and then requesting more from it causes the on-demand entropy sources to trigger reseed, which causes cprng_fast/strong to request more which depletes the pool again which causes on-demand entropy sources to trigger reseed, and so on. To work around this: 2. Set a rate limit on reseeding (advancing the entropy epoch) when kern.entropy.depletion=1; otherwise reseeding gets into a feedback loop when there are on-demand entropy sources like RDRAND/RDSEED. (By default, kern.entropy.depletion=0, so this mainly only affects systems where you're simulating what happens when /dev/random blocks for testing.)
2020-05-07 03:55:13 +03:00
if (__predict_true(!atomic_load_relaxed(&entropy_depletion)) ||
ratecheck(&lasttime, &interval)) {
epoch = E->epoch + 1;
if (epoch == 0 || epoch == (unsigned)-1)
epoch = 1;
atomic_store_relaxed(&E->epoch, epoch);
}
rnd(9): Delete legacy rnd_initial_entropy symbol. Use entropy_epoch() instead. XXX kernel ABI change deleting symbol requires bump
2022-03-19 17:35:08 +03:00
KASSERT(E->epoch != (unsigned)-1);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Notify waiters. */
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold)) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
cv_broadcast(&E->cv);
selnotify(&E->selq, POLLIN|POLLRDNORM, NOTE_SUBMIT);
}
/* Count another notification. */
entropy_notify_evcnt.ev_count++;
}
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
/*
* entropy_consolidate()
*
* Trigger entropy consolidation and wait for it to complete.
*
* This should be used sparingly, not periodically -- requiring
* conscious intervention by the operator or a clear policy
* decision. Otherwise, the kernel will automatically consolidate
* when enough entropy has been gathered into per-CPU pools to
* transition to full entropy.
*/
void
entropy_consolidate(void)
{
uint64_t ticket;
int error;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
ASSERT_SLEEPABLE();
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
mutex_enter(&E->lock);
ticket = entropy_consolidate_evcnt.ev_count;
E->consolidate = true;
cv_broadcast(&E->cv);
while (ticket == entropy_consolidate_evcnt.ev_count) {
error = cv_wait_sig(&E->cv, &E->lock);
if (error)
break;
}
mutex_exit(&E->lock);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* sysctl -w kern.entropy.consolidate=1
*
* Trigger entropy consolidation and wait for it to complete.
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
* Writable only by superuser. This, writing to /dev/random, and
* ioctl(RNDADDDATA) are the only ways for the system to
* consolidate entropy if the operator knows something the kernel
* doesn't about how unpredictable the pending entropy pools are.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
static int
sysctl_entropy_consolidate(SYSCTLFN_ARGS)
{
struct sysctlnode node = *rnode;
entropy: Don't disclose stack garbage in kern.entropy sysctls. kern.entropy.consolidate and kern.entropy.gather are supposed to be write-only -- it doesn't make any sense to read from them, but I suppose it's better to read-as-zero than read-as-stack-secrets!
2022-08-06 02:43:46 +03:00
int arg = 0;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
int error;
node.sysctl_data = &arg;
error = sysctl_lookup(SYSCTLFN_CALL(&node));
if (error || newp == NULL)
return error;
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
if (arg)
entropy_consolidate();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
return error;
}
New sysctl kern.entropy.gather=1 to trigger entropy gathering. Invokes all on-demand RNG sources. This enables HWRNG driver developers to use a dtrace probe on rnd_add_data to examine the data coming out of the HWRNG: dtrace -n 'fbt::rnd_add_data:entry /args[0]->name == "amdccp0"/ { ...examine buffer args[1] length args[2]... }'
2020-05-05 18:31:42 +03:00
/*
* sysctl -w kern.entropy.gather=1
*
* Trigger gathering entropy from all on-demand sources, and wait
* for synchronous sources (but not asynchronous sources) to
* complete. Writable only by superuser.
*/
static int
sysctl_entropy_gather(SYSCTLFN_ARGS)
{
struct sysctlnode node = *rnode;
entropy: Don't disclose stack garbage in kern.entropy sysctls. kern.entropy.consolidate and kern.entropy.gather are supposed to be write-only -- it doesn't make any sense to read from them, but I suppose it's better to read-as-zero than read-as-stack-secrets!
2022-08-06 02:43:46 +03:00
int arg = 0;
New sysctl kern.entropy.gather=1 to trigger entropy gathering. Invokes all on-demand RNG sources. This enables HWRNG driver developers to use a dtrace probe on rnd_add_data to examine the data coming out of the HWRNG: dtrace -n 'fbt::rnd_add_data:entry /args[0]->name == "amdccp0"/ { ...examine buffer args[1] length args[2]... }'
2020-05-05 18:31:42 +03:00
int error;
node.sysctl_data = &arg;
error = sysctl_lookup(SYSCTLFN_CALL(&node));
if (error || newp == NULL)
return error;
if (arg) {
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = entropy_request(ENTROPY_CAPACITY,
ENTROPY_WAIT|ENTROPY_SIG);
New sysctl kern.entropy.gather=1 to trigger entropy gathering. Invokes all on-demand RNG sources. This enables HWRNG driver developers to use a dtrace probe on rnd_add_data to examine the data coming out of the HWRNG: dtrace -n 'fbt::rnd_add_data:entry /args[0]->name == "amdccp0"/ { ...examine buffer args[1] length args[2]... }'
2020-05-05 18:31:42 +03:00
mutex_exit(&E->lock);
}
return 0;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_extract(buf, len, flags)
*
* Extract len bytes from the global entropy pool into buf.
*
entropy(9): Note rules about how to use entropy_extract output.
2022-05-13 12:39:52 +03:00
* Caller MUST NOT expose these bytes directly -- must use them
* ONLY to seed a cryptographic pseudorandom number generator
* (`CPRNG'), a.k.a. deterministic random bit generator (`DRBG'),
* and then erase them. entropy_extract does not, on its own,
* provide backtracking resistance -- it must be combined with a
* PRNG/DRBG that does.
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* This may be used very early at boot, before even entropy_init
* has been called.
*
entropy(9): Note rules about how to use entropy_extract output.
2022-05-13 12:39:52 +03:00
* You generally shouldn't use this directly -- use cprng(9)
* instead.
*
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
* Flags may have:
*
* ENTROPY_WAIT Wait for entropy if not available yet.
* ENTROPY_SIG Allow interruption by a signal during wait.
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
* ENTROPY_HARDFAIL Either fill the buffer with full entropy,
* or fail without filling it at all.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Return zero on success, or error on failure:
*
* EWOULDBLOCK No entropy and ENTROPY_WAIT not set.
* EINTR/ERESTART No entropy, ENTROPY_SIG set, and interrupted.
*
* If ENTROPY_WAIT is set, allowed only in thread context. If
entropy(9): Update comment about where entropy_extract is allowed. As of last month, it is forbidden in all hard interrupt context.
2022-05-13 12:40:02 +03:00
* ENTROPY_WAIT is not set, allowed also in softint context.
* Forbidden in hard interrupt context.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
int
entropy_extract(void *buf, size_t len, int flags)
{
static const struct timeval interval = {.tv_sec = 60, .tv_usec = 0};
static struct timeval lasttime; /* serialized by E->lock */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bool printed = false;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
int s = -1/*XXXGCC*/, error;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
if (ISSET(flags, ENTROPY_WAIT)) {
ASSERT_SLEEPABLE();
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy(9): Forbid entropy_extract in hard interrupt context. With a little additional work, this will let us reduce the global entropy pool lock so it never blocks interrupts.
2022-03-17 02:56:55 +03:00
/* Refuse to operate in interrupt context. */
KASSERT(!cpu_intr_p());
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* If we're cold, we are only contending with interrupts on the
* current CPU, so block them. Otherwise, we are _not_
* contending with interrupts on the current CPU, but we are
* contending with other threads, to exclude them with a mutex.
*/
if (__predict_false(cold))
s = splhigh();
else
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
/* Wait until there is enough entropy in the system. */
error = 0;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->bitsneeded > 0 && E->samplesneeded == 0) {
/*
* We don't have full entropy from reliable sources,
* but we gathered a plausible number of samples from
* other sources such as timers. Try asking for more
* from any sources we can, but don't worry if it
* fails -- best effort.
*/
(void)entropy_request(ENTROPY_CAPACITY, flags);
} else while (E->bitsneeded > 0 && E->samplesneeded > 0) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Ask for more, synchronously if possible. */
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = entropy_request(len, flags);
if (error)
break;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* If we got enough, we're done. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->bitsneeded == 0 || E->samplesneeded == 0) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KASSERT(error == 0);
break;
}
/* If not waiting, stop here. */
if (!ISSET(flags, ENTROPY_WAIT)) {
error = EWOULDBLOCK;
break;
}
/* Wait for some entropy to come in and try again. */
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (!printed) {
printf("entropy: pid %d (%s) waiting for entropy(7)\n",
curproc->p_pid, curproc->p_comm);
printed = true;
}
Log a message when a process blocks due to a lack of entropy. Discussed on tech-kern.
2020-09-29 10:51:01 +03:00
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
if (ISSET(flags, ENTROPY_SIG)) {
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
error = cv_timedwait_sig(&E->cv, &E->lock, hz);
if (error && error != EWOULDBLOCK)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
break;
} else {
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
cv_timedwait(&E->cv, &E->lock, hz);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
}
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
/*
* Count failure -- but fill the buffer nevertheless, unless
* the caller specified ENTROPY_HARDFAIL.
*/
if (error) {
if (ISSET(flags, ENTROPY_HARDFAIL))
goto out;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_extract_fail_evcnt.ev_count++;
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* Report a warning if we haven't yet reached full entropy.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
* This is the only case where we consider entropy to be
* `depleted' without kern.entropy.depletion enabled -- when we
* only have partial entropy, an adversary may be able to
* narrow the state of the pool down to a small number of
* possibilities; the output then enables them to confirm a
* guess, reducing its entropy from the adversary's perspective
* to zero.
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
*
* This should only happen if the operator has chosen to
* consolidate, either through sysctl kern.entropy.consolidate
* or by writing less than full entropy to /dev/random as root
* (which /dev/random promises will immediately affect
* subsequent output, for better or worse).
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->bitsneeded > 0 && E->samplesneeded > 0) {
if (__predict_false(E->epoch == (unsigned)-1) &&
ratecheck(&lasttime, &interval)) {
entropy(9): Improve entropy warning messages and documentation. - For the main warning message, use less jargon, say `security', and cite the entropy(7) man page for further reading. Document this in rnd(4) and entropy(7). - For the debug-only warning message, say `entropy' only once and omit it from the rnd(4) man page -- it's not very important unless you're debugging the kernel in which case you probably know what you're doing enough to not need the text explained in the man page.
2022-03-20 21:19:57 +03:00
printf("WARNING:"
" system needs entropy for security;"
" see entropy(7)\n");
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
}
atomic_store_relaxed(&E->bitsneeded, MINENTROPYBITS);
atomic_store_relaxed(&E->samplesneeded, MINSAMPLES);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/* Extract data from the pool, and `deplete' if we're doing that. */
entpool_extract(&E->pool, buf, len);
if (__predict_false(atomic_load_relaxed(&entropy_depletion)) &&
error == 0) {
unsigned cost = MIN(len, ENTROPY_CAPACITY)*NBBY;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
unsigned bitsneeded = E->bitsneeded;
unsigned samplesneeded = E->samplesneeded;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bitsneeded += MIN(MINENTROPYBITS - bitsneeded, cost);
samplesneeded += MIN(MINSAMPLES - samplesneeded, cost);
atomic_store_relaxed(&E->bitsneeded, bitsneeded);
atomic_store_relaxed(&E->samplesneeded, samplesneeded);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_deplete_evcnt.ev_count++;
}
New system call getrandom() compatible with Linux and others. Three ways to call: getrandom(p, n, 0) Blocks at boot until full entropy. Returns up to n bytes at p; guarantees up to 256 bytes even if interrupted after blocking. getrandom(0,0,0) serves as an entropy barrier: return only after system has full entropy. getrandom(p, n, GRND_INSECURE) Never blocks. Guarantees up to 256 bytes even if interrupted. Equivalent to /dev/urandom. Safe only after successful getrandom(...,0), getrandom(...,GRND_RANDOM), or read from /dev/random. getrandom(p, n, GRND_RANDOM) May block at any time. Returns up to n bytes at p, but no guarantees about how many -- may return as short as 1 byte. Equivalent to /dev/random. Legacy. Provided only for source compatibility with Linux. Can also use flags|GRND_NONBLOCK to fail with EWOULDBLOCK/EAGAIN without producing any output instead of blocking. - The combination GRND_INSECURE|GRND_NONBLOCK is the same as GRND_INSECURE, since GRND_INSECURE never blocks anyway. - The combinations GRND_INSECURE|GRND_RANDOM and GRND_INSECURE|GRND_RANDOM|GRND_NONBLOCK are nonsensical and fail with EINVAL. As proposed on tech-userlevel, tech-crypto, tech-security, and tech-kern, and subsequently adopted by core (minus the getentropy part of the proposal, because other operating systems and participants in the discussion couldn't come to an agreement about getentropy and blocking semantics): https://mail-index.netbsd.org/tech-userlevel/2020/05/02/msg012333.html
2020-08-14 03:53:15 +03:00
out: /* Release the global lock and return the error. */
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_false(cold))
splx(s);
else
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
return error;
}
/*
* entropy_poll(events)
*
* Return the subset of events ready, and if it is not all of
* events, record curlwp as waiting for entropy.
*/
int
entropy_poll(int events)
{
int revents = 0;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Always ready for writing. */
revents |= events & (POLLOUT|POLLWRNORM);
/* Narrow it down to reads. */
events &= POLLIN|POLLRDNORM;
if (events == 0)
return revents;
/*
* If we have reached full entropy and we're not depleting
* entropy, we are forever ready.
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (__predict_true(atomic_load_relaxed(&E->bitsneeded) == 0 ||
atomic_load_relaxed(&E->samplesneeded) == 0) &&
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
__predict_true(!atomic_load_relaxed(&entropy_depletion)))
return revents | events;
/*
* Otherwise, check whether we need entropy under the lock. If
* we don't, we're ready; if we do, add ourselves to the queue.
*/
mutex_enter(&E->lock);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->bitsneeded == 0 || E->samplesneeded == 0)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
revents |= events;
else
selrecord(curlwp, &E->selq);
mutex_exit(&E->lock);
return revents;
}
/*
* filt_entropy_read_detach(kn)
*
* struct filterops::f_detach callback for entropy read events:
* remove kn from the list of waiters.
*/
static void
filt_entropy_read_detach(struct knote *kn)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
Use sel{record,remove}_knote().
2020-12-11 06:00:09 +03:00
selremove_knote(&E->selq, kn);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
}
/*
* filt_entropy_read_event(kn, hint)
*
* struct filterops::f_event callback for entropy read events:
* poll for entropy. Caller must hold the global entropy lock if
* hint is NOTE_SUBMIT, and must not if hint is not NOTE_SUBMIT.
*/
static int
filt_entropy_read_event(struct knote *kn, long hint)
{
int ret;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Acquire the lock, if caller is outside entropy subsystem. */
if (hint == NOTE_SUBMIT)
KASSERT(mutex_owned(&E->lock));
else
mutex_enter(&E->lock);
/*
* If we still need entropy, can't read anything; if not, can
* read arbitrarily much.
*/
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (E->bitsneeded != 0 && E->samplesneeded != 0) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
ret = 0;
} else {
if (atomic_load_relaxed(&entropy_depletion))
random(4): Report number of bytes ready to read, not number of bits. Only affects systems with the diagnostic and testing option kern.entropy.depletion=1. XXX pullup-10
2023-03-01 11:13:54 +03:00
kn->kn_data = ENTROPY_CAPACITY; /* bytes */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
else
kn->kn_data = MIN(INT64_MAX, SSIZE_MAX);
ret = 1;
}
/* Release the lock, if caller is outside entropy subsystem. */
if (hint == NOTE_SUBMIT)
KASSERT(mutex_owned(&E->lock));
else
mutex_exit(&E->lock);
return ret;
}
entropy_read_filtops is MPSAFE.
2021-09-26 18:10:51 +03:00
/* XXX Makes sense only for /dev/u?random. */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
static const struct filterops entropy_read_filtops = {
entropy_read_filtops is MPSAFE.
2021-09-26 18:10:51 +03:00
.f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
.f_attach = NULL,
.f_detach = filt_entropy_read_detach,
.f_event = filt_entropy_read_event,
};
/*
* entropy_kqfilter(kn)
*
* Register kn to receive entropy event notifications. May be
* EVFILT_READ or EVFILT_WRITE; anything else yields EINVAL.
*/
int
entropy_kqfilter(struct knote *kn)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
switch (kn->kn_filter) {
case EVFILT_READ:
/* Enter into the global select queue. */
mutex_enter(&E->lock);
kn->kn_fop = &entropy_read_filtops;
Use sel{record,remove}_knote().
2020-12-11 06:00:09 +03:00
selrecord_knote(&E->selq, kn);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
return 0;
case EVFILT_WRITE:
/* Can always dump entropy into the system. */
kn->kn_fop = &seltrue_filtops;
return 0;
default:
return EINVAL;
}
}
/*
* rndsource_setcb(rs, get, getarg)
*
* Set the request callback for the entropy source rs, if it can
* provide entropy on demand. Must precede rnd_attach_source.
*/
void
rndsource_setcb(struct krndsource *rs, void (*get)(size_t, void *),
void *getarg)
{
rs->get = get;
rs->getarg = getarg;
}
/*
* rnd_attach_source(rs, name, type, flags)
*
* Attach the entropy source rs. Must be done after
* rndsource_setcb, if any, and before any calls to rnd_add_data.
*/
void
rnd_attach_source(struct krndsource *rs, const char *name, uint32_t type,
uint32_t flags)
{
uint32_t extra[4];
unsigned i = 0;
entropy(9): Allow changing flags on all entropy sources at once. Entropy sources should all have nonempty names, and this will enable an operator to, for example, disable all but a specific entropy source. XXX pullup-10
2023-03-03 15:52:49 +03:00
KASSERTMSG(name[0] != '\0', "rndsource must have nonempty name");
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Grab cycle counter to mix extra into the pool. */
extra[i++] = entropy_timer();
/*
* Apply some standard flags:
*
* - We do not bother with network devices by default, for
* hysterical raisins (perhaps: because it is often the case
* that an adversary can influence network packet timings).
*/
switch (type) {
case RND_TYPE_NET:
flags |= RND_FLAG_NO_COLLECT;
break;
}
/* Sanity-check the callback if RND_FLAG_HASCB is set. */
KASSERT(!ISSET(flags, RND_FLAG_HASCB) || rs->get != NULL);
/* Initialize the random source. */
memset(rs->name, 0, sizeof(rs->name)); /* paranoia */
strlcpy(rs->name, name, sizeof(rs->name));
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
memset(&rs->time_delta, 0, sizeof(rs->time_delta));
memset(&rs->value_delta, 0, sizeof(rs->value_delta));
Initialize struct krndsource::total to zero. Avoids bogus counts reported by `rndctl -l' in the event that the caller neglected to zero the rndsource ahead of time.
2020-05-03 09:33:59 +03:00
rs->total = 0;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rs->type = type;
rs->flags = flags;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (entropy_percpu != NULL)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rs->state = percpu_alloc(sizeof(struct rndsource_cpu));
extra[i++] = entropy_timer();
/* Wire it into the global list of random sources. */
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
LIST_INSERT_HEAD(&E->sources, rs, list);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
extra[i++] = entropy_timer();
/* Request that it provide entropy ASAP, if we can. */
if (ISSET(flags, RND_FLAG_HASCB))
(*rs->get)(ENTROPY_CAPACITY, rs->getarg);
extra[i++] = entropy_timer();
/* Mix the extra into the pool. */
KASSERT(i == __arraycount(extra));
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
entropy_enter(extra, sizeof extra, 0, /*count*/__predict_true(!cold));
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(extra, 0, sizeof extra);
}
/*
* rnd_detach_source(rs)
*
* Detach the entropy source rs. May sleep waiting for users to
* drain. Further use is not allowed.
*/
void
rnd_detach_source(struct krndsource *rs)
{
/*
* If we're cold (shouldn't happen, but hey), just remove it
* from the list -- there's nothing allocated.
*/
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_false(cold) && entropy_percpu == NULL) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_REMOVE(rs, list);
return;
}
/* We may have to wait for entropy_request. */
ASSERT_SLEEPABLE();
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
/* Wait until the source list is not in use, and remove it. */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
while (E->sourcelock)
entropy: Use a separate condvar for rndsource list lock. Otherwise, two processes both waiting for entropy will dance around waking each other up (by releasing the rndsource list lock) and going back to sleep (waiting for entropy). Witnessed on the armv7 testbed when /etc/security presumably ran twice over a >day-long test, until the metaphorical plug got pulled: net/if_ipsec/t_ipsec_natt (509/888): 2 test cases ipsecif_natt_transport_null: [ 37123.2631856] entropy: pid 1005 (dd) blocking due to lack of entropy [256.523317s] Failed: atf-check failed; see the output of the test for details ipsecif_natt_transport_rijndaelcbc: [274.370791s] Failed: atf-check failed; see the output of the test for details [532.486697s] ... puffs_lstat_symlink: [ 123442.1606517] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1835067] entropy: pid 1005 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 1005 (dd) blocking due to lack of entropy ...
2021-01-14 02:53:23 +03:00
cv_wait(&E->sourcelock_cv, &E->lock);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
LIST_REMOVE(rs, list);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
/* Free the per-CPU data. */
percpu_free(rs->state, sizeof(struct rndsource_cpu));
}
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
/*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* rnd_lock_sources(flags)
*
* Lock the list of entropy sources. Caller must hold the global
* entropy lock. If successful, no rndsource will go away until
* rnd_unlock_sources even while the caller releases the global
* entropy lock.
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* May be called very early at boot, before entropy_init.
*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* If flags & ENTROPY_WAIT, wait for concurrent access to finish.
* If flags & ENTROPY_SIG, allow interruption by signal.
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
*/
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
static int __attribute__((warn_unused_result))
rnd_lock_sources(int flags)
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
{
int error;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(__predict_false(cold) || mutex_owned(&E->lock));
KASSERT(!cpu_intr_p());
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
while (E->sourcelock) {
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
if (!ISSET(flags, ENTROPY_WAIT))
return EWOULDBLOCK;
if (ISSET(flags, ENTROPY_SIG)) {
error = cv_wait_sig(&E->sourcelock_cv, &E->lock);
if (error)
return error;
} else {
cv_wait(&E->sourcelock_cv, &E->lock);
}
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
}
E->sourcelock = curlwp;
return 0;
}
/*
* rnd_unlock_sources()
*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* Unlock the list of sources after rnd_lock_sources. Caller must
* hold the global entropy lock.
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
*
* May be called very early at boot, before entropy_init.
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
*/
static void
rnd_unlock_sources(void)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(__predict_false(cold) || mutex_owned(&E->lock));
KASSERT(!cpu_intr_p());
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
Eliminate curcpu_available() hack. The entropy subsystem is no longer used before curcpu() and curlwp are available on x86.
2020-05-08 03:54:44 +03:00
KASSERTMSG(E->sourcelock == curlwp, "lwp %p releasing lock held by %p",
curlwp, E->sourcelock);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
E->sourcelock = NULL;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
entropy: Use a separate condvar for rndsource list lock. Otherwise, two processes both waiting for entropy will dance around waking each other up (by releasing the rndsource list lock) and going back to sleep (waiting for entropy). Witnessed on the armv7 testbed when /etc/security presumably ran twice over a >day-long test, until the metaphorical plug got pulled: net/if_ipsec/t_ipsec_natt (509/888): 2 test cases ipsecif_natt_transport_null: [ 37123.2631856] entropy: pid 1005 (dd) blocking due to lack of entropy [256.523317s] Failed: atf-check failed; see the output of the test for details ipsecif_natt_transport_rijndaelcbc: [274.370791s] Failed: atf-check failed; see the output of the test for details [532.486697s] ... puffs_lstat_symlink: [ 123442.1606517] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1835067] entropy: pid 1005 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 9499 (dd) blocking due to lack of entropy [ 123442.1944600] entropy: pid 1005 (dd) blocking due to lack of entropy ...
2021-01-14 02:53:23 +03:00
cv_signal(&E->sourcelock_cv);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
}
/*
* rnd_sources_locked()
*
* True if we hold the list of rndsources locked, for diagnostic
* assertions.
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
*
* May be called very early at boot, before entropy_init.
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
*/
Mark rnd_sources_locked __diagused -- only for KASSERTs.
2020-04-30 23:06:40 +03:00
static bool __diagused
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
rnd_sources_locked(void)
{
Eliminate curcpu_available() hack. The entropy subsystem is no longer used before curcpu() and curlwp are available on x86.
2020-05-08 03:54:44 +03:00
return E->sourcelock == curlwp;
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* entropy_request(nbytes, flags)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Request nbytes bytes of entropy from all sources in the system.
* OK if we overdo it. Caller must hold the global entropy lock;
* will release and re-acquire it.
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* May be called very early at boot, before entropy_init.
*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* If flags & ENTROPY_WAIT, wait for concurrent access to finish.
* If flags & ENTROPY_SIG, allow interruption by signal.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
static int
entropy_request(size_t nbytes, int flags)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
struct krndsource *rs;
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
int error;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(__predict_false(cold) || mutex_owned(&E->lock));
KASSERT(!cpu_intr_p());
if ((flags & ENTROPY_WAIT) != 0 && __predict_false(!cold))
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
ASSERT_SLEEPABLE();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
* Lock the list of entropy sources to block rnd_detach_source
* until we're done, and to serialize calls to the entropy
* callbacks as guaranteed to drivers.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = rnd_lock_sources(flags);
if (error)
return error;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy_request_evcnt.ev_count++;
/* Clamp to the maximum reasonable request. */
nbytes = MIN(nbytes, ENTROPY_CAPACITY);
/* Walk the list of sources. */
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
LIST_FOREACH(rs, &E->sources, list) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Skip sources without callbacks. */
if (!ISSET(rs->flags, RND_FLAG_HASCB))
continue;
Don't invoke callbacks of rndsources with collection disabled.
2020-05-12 23:50:17 +03:00
/*
* Skip sources that are disabled altogether -- we
* would just ignore their samples anyway.
*/
if (ISSET(rs->flags, RND_FLAG_NO_COLLECT))
continue;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Drop the lock while we call the callback. */
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
(*rs->get)(nbytes, rs->getarg);
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_true(!cold))
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
}
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
/* Request done; unlock the list of entropy sources. */
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
rnd_unlock_sources();
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
return 0;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
static inline uint32_t
rnd_delta_estimate(rnd_delta_t *d, uint32_t v, int32_t delta)
{
int32_t delta2, delta3;
/*
* Calculate the second and third order differentials
*/
delta2 = d->dx - delta;
if (delta2 < 0)
delta2 = -delta2; /* XXX arithmetic overflow */
delta3 = d->d2x - delta2;
if (delta3 < 0)
delta3 = -delta3; /* XXX arithmetic overflow */
d->x = v;
d->dx = delta;
d->d2x = delta2;
/*
* If any delta is 0, we got no entropy. If all are non-zero, we
* might have something.
*/
if (delta == 0 || delta2 == 0 || delta3 == 0)
return 0;
return 1;
}
static inline uint32_t
rnd_dt_estimate(struct krndsource *rs, uint32_t t)
{
int32_t delta;
uint32_t ret;
rnd_delta_t *d;
struct rndsource_cpu *rc;
rc = percpu_getref(rs->state);
d = &rc->rc_timedelta;
if (t < d->x) {
delta = UINT32_MAX - d->x + t;
} else {
delta = d->x - t;
}
if (delta < 0) {
delta = -delta; /* XXX arithmetic overflow */
}
ret = rnd_delta_estimate(d, t, delta);
KASSERT(d->x == t);
KASSERT(d->dx == delta);
percpu_putref(rs->state);
return ret;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* rnd_add_uint32(rs, value)
*
* Enter 32 bits of data from an entropy source into the pool.
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* May be called from any context or with spin locks held, but may
* drop data.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* This is meant for cheaply taking samples from devices that
* aren't designed to be hardware random number generators.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
void
rnd_add_uint32(struct krndsource *rs, uint32_t value)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
bool intr_p = true;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
rnd_add_data_internal(rs, &value, sizeof value, 0, intr_p);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
void
_rnd_add_uint32(struct krndsource *rs, uint32_t value)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
bool intr_p = true;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
rnd_add_data_internal(rs, &value, sizeof value, 0, intr_p);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
void
_rnd_add_uint64(struct krndsource *rs, uint64_t value)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
bool intr_p = true;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
rnd_add_data_internal(rs, &value, sizeof value, 0, intr_p);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
/*
* rnd_add_data(rs, buf, len, entropybits)
*
* Enter data from an entropy source into the pool, with a
* driver's estimate of how much entropy the physical source of
* the data has. If RND_FLAG_NO_ESTIMATE, we ignore the driver's
* estimate and treat it as zero.
*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* rs MAY but SHOULD NOT be NULL. If rs is NULL, MUST NOT be
* called from interrupt context or with spin locks held.
*
* If rs is non-NULL, MAY but SHOULD NOT be called from interrupt
* context, in which case act like rnd_add_data_intr -- if the
* sample buffer is full, schedule a softint and drop any
* additional data on the floor. (This may change later once we
* fix drivers that still call this from interrupt context to use
* rnd_add_data_intr instead.) MUST NOT be called with spin locks
* held if not in hard interrupt context -- i.e., MUST NOT be
* called in thread context or softint context with spin locks
* held.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
void
rnd_add_data(struct krndsource *rs, const void *buf, uint32_t len,
uint32_t entropybits)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
bool intr_p = cpu_intr_p(); /* XXX make this unconditionally false */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
/*
* Weird legacy exception that we should rip out and replace by
* creating new rndsources to attribute entropy to the callers:
* If there's no rndsource, just enter the data and time now.
*/
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
if (rs == NULL) {
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
uint32_t extra;
KASSERT(!intr_p);
KASSERTMSG(howmany(entropybits, NBBY) <= len,
"%s: impossible entropy rate:"
" %"PRIu32" bits in %"PRIu32"-byte string",
rs ? rs->name : "(anonymous)", entropybits, len);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter(buf, len, entropybits, /*count*/false);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
extra = entropy_timer();
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter(&extra, sizeof extra, 0, /*count*/false);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
explicit_memset(&extra, 0, sizeof extra);
return;
}
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
rnd_add_data_internal(rs, buf, len, entropybits, intr_p);
}
/*
* rnd_add_data_intr(rs, buf, len, entropybits)
*
* Try to enter data from an entropy source into the pool, with a
* driver's estimate of how much entropy the physical source of
* the data has. If RND_FLAG_NO_ESTIMATE, we ignore the driver's
* estimate and treat it as zero. If the sample buffer is full,
* schedule a softint and drop any additional data on the floor.
*/
void
rnd_add_data_intr(struct krndsource *rs, const void *buf, uint32_t len,
uint32_t entropybits)
{
bool intr_p = true;
rnd_add_data_internal(rs, buf, len, entropybits, intr_p);
}
/*
* rnd_add_data_internal(rs, buf, len, entropybits, intr_p)
*
* Internal subroutine to decide whether or not to enter data or
* timing for a particular rndsource, and if so, to enter it.
*
* intr_p is true for callers from interrupt context or spin locks
* held, and false for callers from thread or soft interrupt
* context and no spin locks held.
*/
static void
rnd_add_data_internal(struct krndsource *rs, const void *buf, uint32_t len,
uint32_t entropybits, bool intr_p)
{
uint32_t flags;
KASSERTMSG(howmany(entropybits, NBBY) <= len,
"%s: impossible entropy rate:"
" %"PRIu32" bits in %"PRIu32"-byte string",
rs ? rs->name : "(anonymous)", entropybits, len);
entropy(9): Avoid race between rnd_add_data and ioctl(RNDCTL). XXX pullup-10
2023-05-24 23:22:23 +03:00
/*
* Hold up the reset xcall before it zeroes the entropy counts
* on this CPU or globally. Otherwise, we might leave some
* nonzero entropy attributed to an untrusted source in the
* event of a race with a change to flags.
*/
kpreempt_disable();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Load a snapshot of the flags. Ioctl may change them under us. */
flags = atomic_load_relaxed(&rs->flags);
/*
* Skip if:
* - we're not collecting entropy, or
* - the operator doesn't want to collect entropy from this, or
* - neither data nor timings are being collected from this.
*/
if (!atomic_load_relaxed(&entropy_collection) ||
ISSET(flags, RND_FLAG_NO_COLLECT) ||
!ISSET(flags, RND_FLAG_COLLECT_VALUE|RND_FLAG_COLLECT_TIME))
entropy(9): Avoid race between rnd_add_data and ioctl(RNDCTL). XXX pullup-10
2023-05-24 23:22:23 +03:00
goto out;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* If asked, ignore the estimate. */
if (ISSET(flags, RND_FLAG_NO_ESTIMATE))
entropybits = 0;
/* If we are collecting data, enter them. */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
if (ISSET(flags, RND_FLAG_COLLECT_VALUE)) {
rnd_add_data_1(rs, buf, len, entropybits, /*count*/false,
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
RND_FLAG_COLLECT_VALUE, intr_p);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* If we are collecting timings, enter one. */
if (ISSET(flags, RND_FLAG_COLLECT_TIME)) {
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
uint32_t extra;
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
bool count;
/* Sample a timer. */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
extra = entropy_timer();
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
/* If asked, do entropy estimation on the time. */
if ((flags & (RND_FLAG_ESTIMATE_TIME|RND_FLAG_NO_ESTIMATE)) ==
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
RND_FLAG_ESTIMATE_TIME && __predict_true(!cold))
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
count = rnd_dt_estimate(rs, extra);
else
count = false;
rnd_add_data_1(rs, &extra, sizeof extra, 0, count,
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
RND_FLAG_COLLECT_TIME, intr_p);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy(9): Avoid race between rnd_add_data and ioctl(RNDCTL). XXX pullup-10
2023-05-24 23:22:23 +03:00
out: /* Allow concurrent changes to flags to finish. */
kpreempt_enable();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
static unsigned
add_sat(unsigned a, unsigned b)
{
unsigned c = a + b;
return (c < a ? UINT_MAX : c);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
* rnd_add_data_1(rs, buf, len, entropybits, count, flag)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*
* Internal subroutine to call either entropy_enter_intr, if we're
* in interrupt context, or entropy_enter if not, and to count the
* entropy in an rndsource.
*/
static void
rnd_add_data_1(struct krndsource *rs, const void *buf, uint32_t len,
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
uint32_t entropybits, bool count, uint32_t flag, bool intr_p)
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
{
bool fullyused;
/*
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
* For the interrupt-like path, use entropy_enter_intr and take
* note of whether it consumed the full sample; otherwise, use
* entropy_enter, which always consumes the full sample.
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*/
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (intr_p) {
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
fullyused = entropy_enter_intr(buf, len, entropybits, count);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
} else {
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
entropy_enter(buf, len, entropybits, count);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
fullyused = true;
}
/*
* If we used the full sample, note how many bits were
* contributed from this source.
*/
if (fullyused) {
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
if (__predict_false(cold)) {
const int s = splhigh();
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
rs->total = add_sat(rs->total, entropybits);
switch (flag) {
case RND_FLAG_COLLECT_TIME:
rs->time_delta.insamples =
add_sat(rs->time_delta.insamples, 1);
break;
case RND_FLAG_COLLECT_VALUE:
rs->value_delta.insamples =
add_sat(rs->value_delta.insamples, 1);
break;
}
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
splx(s);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
} else {
struct rndsource_cpu *rc = percpu_getref(rs->state);
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
atomic_store_relaxed(&rc->rc_entropybits,
add_sat(rc->rc_entropybits, entropybits));
switch (flag) {
case RND_FLAG_COLLECT_TIME:
atomic_store_relaxed(&rc->rc_timesamples,
add_sat(rc->rc_timesamples, 1));
break;
case RND_FLAG_COLLECT_VALUE:
atomic_store_relaxed(&rc->rc_datasamples,
add_sat(rc->rc_datasamples, 1));
break;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
percpu_putref(rs->state);
}
}
}
/*
* rnd_add_data_sync(rs, buf, len, entropybits)
*
* Same as rnd_add_data. Originally used in rndsource callbacks,
* to break an unnecessary cycle; no longer really needed.
*/
void
rnd_add_data_sync(struct krndsource *rs, const void *buf, uint32_t len,
uint32_t entropybits)
{
rnd_add_data(rs, buf, len, entropybits);
}
/*
* rndsource_entropybits(rs)
*
* Return approximately the number of bits of entropy that have
* been contributed via rs so far. Approximate if other CPUs may
* be calling rnd_add_data concurrently.
*/
static unsigned
rndsource_entropybits(struct krndsource *rs)
{
unsigned nbits = rs->total;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
KASSERT(rnd_sources_locked());
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
percpu_foreach(rs->state, rndsource_entropybits_cpu, &nbits);
return nbits;
}
static void
rndsource_entropybits_cpu(void *ptr, void *cookie, struct cpu_info *ci)
{
struct rndsource_cpu *rc = ptr;
unsigned *nbitsp = cookie;
unsigned cpu_nbits;
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
cpu_nbits = atomic_load_relaxed(&rc->rc_entropybits);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
*nbitsp += MIN(UINT_MAX - *nbitsp, cpu_nbits);
}
/*
* rndsource_to_user(rs, urs)
*
* Copy a description of rs out to urs for userland.
*/
static void
rndsource_to_user(struct krndsource *rs, rndsource_t *urs)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
KASSERT(rnd_sources_locked());
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Avoid kernel memory disclosure. */
memset(urs, 0, sizeof(*urs));
CTASSERT(sizeof(urs->name) == sizeof(rs->name));
strlcpy(urs->name, rs->name, sizeof(urs->name));
urs->total = rndsource_entropybits(rs);
urs->type = rs->type;
urs->flags = atomic_load_relaxed(&rs->flags);
}
/*
* rndsource_to_user_est(rs, urse)
*
* Copy a description of rs and estimation statistics out to urse
* for userland.
*/
static void
rndsource_to_user_est(struct krndsource *rs, rndsource_est_t *urse)
{
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
KASSERT(rnd_sources_locked());
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Avoid kernel memory disclosure. */
memset(urse, 0, sizeof(*urse));
/* Copy out the rndsource description. */
rndsource_to_user(rs, &urse->rt);
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
/* Gather the statistics. */
urse->dt_samples = rs->time_delta.insamples;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
urse->dt_total = 0;
entropy: Record number of time and data samples for userland. This more or less follows the semantics of the RNDGETESTNUM and RNDGETESTNAME ioctls to restore useful `rndctl -lv' output. Specifically: We count the number of time or data samples entered with rnd_add_*. Previously it would count the total number of 32-bit words in the data, rather than the number of rnd_add_* calls that enter data, but I think the number of calls makes more sense here.
2021-01-16 05:21:26 +03:00
urse->dv_samples = rs->value_delta.insamples;
urse->dv_total = urse->rt.total;
percpu_foreach(rs->state, rndsource_to_user_est_cpu, urse);
}
static void
rndsource_to_user_est_cpu(void *ptr, void *cookie, struct cpu_info *ci)
{
struct rndsource_cpu *rc = ptr;
rndsource_est_t *urse = cookie;
urse->dt_samples = add_sat(urse->dt_samples,
atomic_load_relaxed(&rc->rc_timesamples));
urse->dv_samples = add_sat(urse->dv_samples,
atomic_load_relaxed(&rc->rc_datasamples));
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
/*
* entropy_reset_xc(arg1, arg2)
*
* Reset the current CPU's pending entropy to zero.
*/
static void
entropy_reset_xc(void *arg1 __unused, void *arg2 __unused)
{
uint32_t extra = entropy_timer();
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
struct entropy_cpu_lock lock;
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
struct entropy_cpu *ec;
/*
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
* With the per-CPU state locked, zero the pending count and
* enter a cycle count for fun.
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
*/
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
ec = entropy_cpu_get(&lock);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
ec->ec_bitspending = 0;
ec->ec_samplespending = 0;
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
entpool_enter(ec->ec_pool, &extra, sizeof extra);
entropy(9): Factor out logic to lock and unlock per-CPU state. No functional change intended.
2022-03-20 16:17:09 +03:00
entropy_cpu_put(&lock, ec);
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/*
* entropy_ioctl(cmd, data)
*
* Handle various /dev/random ioctl queries.
*/
int
entropy_ioctl(unsigned long cmd, void *data)
{
struct krndsource *rs;
bool privileged;
int error;
entropy(9): Simplify stages. Split interrupt vs non-interrupt paths. - Nix the entropy stage (cold, warm, hot). Just use the usual kernel `cold' (cold: single-core, single-thread; interrupts may happen), and don't make any three-way distinction about whether interrupts or threads or other CPUs can be running. Instead, while cold, use splhigh/splx or forbid paths to come from interrupt context, and while warm, use mutex or the per-CPU hard and soft interrupt paths for low latency. This comes at a small cost to some interrupt latency, since we may stir the pool in interrupt context -- but only for a very short window early at boot between configure and configure2, so it's hard to imagine it matters much. - Allow rnd_add_uint32 to run in hard interrupt context or with spin locks held, but defer processing to softint and drop samples on the floor if buffer is full. This is mainly used for cheaply tossing samples from drivers for non-HWRNG devices into the entropy pool, so it is often used from interrupt context and/or under spin locks. - New rnd_add_data_intr provides the interrupt-like data entry path for arbitrary buffers and driver-specified entropy estimates: defer processing to softint and drop samples on the floor if buffer is full. - Document that rnd_add_data is forbidden under spin locks outside interrupt context (will crash in LOCKDEBUG), and inadvisable in interrupt context (but technically permitted just in case there are compatibility issues for now); later we can forbid it altogether in interrupt context or under spin locks. - Audit all uses of rnd_add_data to use rnd_add_data_intr where it might be used in interrupt context or under a spin lock. This fixes a regression from last year when the global entropy lock was changed from IPL_VM (spin) to IPL_SOFTSERIAL (adaptive). Thought I'd caught all the problems from that, but another one bit three different people this week, presumably because of recent changes that led to more non-HWRNG drivers entering the entropy consolidation path from rnd_add_uint32. In my attempt to preserve the rnd(9) API for the (now long-since abandoned) prospect of pullup to netbsd-9 in my rewrite of the entropy subsystem in 2020, I didn't introduce a separate entry point for entering entropy from interrupt context or equivalent, i.e., spin locks held, and instead made rnd_add_data rely on cpu_intr_p() to decide whether to process the whole sample under a lock or only take as much as there's buffer space for before scheduling a softint. In retrospect, that was a mistake (though perhaps not as much of a mistake as other entropy API decisions...), a mistake which is finally getting rectified now by rnd_add_data_intr. XXX pullup-10
2023-08-04 10:38:53 +03:00
KASSERT(!cold);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
/* Verify user's authorization to perform the ioctl. */
switch (cmd) {
case RNDGETENTCNT:
case RNDGETPOOLSTAT:
case RNDGETSRCNUM:
case RNDGETSRCNAME:
case RNDGETESTNUM:
case RNDGETESTNAME:
don't opencode kauth_cred_get()
2021-09-21 17:54:26 +03:00
error = kauth_authorize_device(kauth_cred_get(),
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KAUTH_DEVICE_RND_GETPRIV, NULL, NULL, NULL, NULL);
break;
case RNDCTL:
don't opencode kauth_cred_get()
2021-09-21 17:54:26 +03:00
error = kauth_authorize_device(kauth_cred_get(),
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KAUTH_DEVICE_RND_SETPRIV, NULL, NULL, NULL, NULL);
break;
case RNDADDDATA:
don't opencode kauth_cred_get()
2021-09-21 17:54:26 +03:00
error = kauth_authorize_device(kauth_cred_get(),
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KAUTH_DEVICE_RND_ADDDATA, NULL, NULL, NULL, NULL);
/* Ascertain whether the user's inputs should be counted. */
don't opencode kauth_cred_get()
2021-09-21 17:54:26 +03:00
if (kauth_authorize_device(kauth_cred_get(),
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
KAUTH_DEVICE_RND_ADDDATA_ESTIMATE,
NULL, NULL, NULL, NULL) == 0)
privileged = true;
break;
default: {
/*
* XXX Hack to avoid changing module ABI so this can be
* pulled up. Later, we can just remove the argument.
*/
static const struct fileops fops = {
.fo_ioctl = rnd_system_ioctl,
};
struct file f = {
.f_ops = &fops,
};
MODULE_HOOK_CALL(rnd_ioctl_50_hook, (&f, cmd, data),
enosys(), error);
#if defined(_LP64)
if (error == ENOSYS)
MODULE_HOOK_CALL(rnd_ioctl32_50_hook, (&f, cmd, data),
enosys(), error);
#endif
if (error == ENOSYS)
error = ENOTTY;
break;
}
}
/* If anything went wrong with authorization, stop here. */
if (error)
return error;
/* Dispatch on the command. */
switch (cmd) {
case RNDGETENTCNT: { /* Get current entropy count in bits. */
uint32_t *countp = data;
mutex_enter(&E->lock);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
*countp = MINENTROPYBITS - E->bitsneeded;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDGETPOOLSTAT: { /* Get entropy pool statistics. */
rndpoolstat_t *pstat = data;
mutex_enter(&E->lock);
/* parameters */
pstat->poolsize = ENTPOOL_SIZE/sizeof(uint32_t); /* words */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
pstat->threshold = MINENTROPYBITS/NBBY; /* bytes */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
pstat->maxentropy = ENTROPY_CAPACITY*NBBY; /* bits */
/* state */
pstat->added = 0; /* XXX total entropy_enter count */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
pstat->curentropy = MINENTROPYBITS - E->bitsneeded; /* bits */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
pstat->removed = 0; /* XXX total entropy_extract count */
pstat->discarded = 0; /* XXX bits of entropy beyond capacity */
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
/*
* This used to be bits of data fabricated in some
* sense; we'll take it to mean number of samples,
* excluding the bits of entropy from HWRNG or seed.
*/
pstat->generated = MINSAMPLES - E->samplesneeded;
pstat->generated -= MIN(pstat->generated, pstat->curentropy);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDGETSRCNUM: { /* Get entropy sources by number. */
rndstat_t *stat = data;
uint32_t start = 0, i = 0;
/* Skip if none requested; fail if too many requested. */
if (stat->count == 0)
break;
if (stat->count > RND_MAXSTATCOUNT)
return EINVAL;
/*
* Under the lock, find the first one, copy out as many
* as requested, and report how many we copied out.
*/
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = rnd_lock_sources(ENTROPY_WAIT|ENTROPY_SIG);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (error) {
mutex_exit(&E->lock);
return error;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_FOREACH(rs, &E->sources, list) {
if (start++ == stat->start)
break;
}
while (i < stat->count && rs != NULL) {
Missed a spot! (Part II(b) of no percpu_foreach under spin lock.)
2020-04-30 20:16:00 +03:00
mutex_exit(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rndsource_to_user(rs, &stat->source[i++]);
Missed a spot! (Part II(b) of no percpu_foreach under spin lock.)
2020-04-30 20:16:00 +03:00
mutex_enter(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rs = LIST_NEXT(rs, list);
}
KASSERT(i <= stat->count);
stat->count = i;
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
rnd_unlock_sources();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDGETESTNUM: { /* Get sources and estimates by number. */
rndstat_est_t *estat = data;
uint32_t start = 0, i = 0;
/* Skip if none requested; fail if too many requested. */
if (estat->count == 0)
break;
if (estat->count > RND_MAXSTATCOUNT)
return EINVAL;
/*
* Under the lock, find the first one, copy out as many
* as requested, and report how many we copied out.
*/
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = rnd_lock_sources(ENTROPY_WAIT|ENTROPY_SIG);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (error) {
mutex_exit(&E->lock);
return error;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_FOREACH(rs, &E->sources, list) {
if (start++ == estat->start)
break;
}
while (i < estat->count && rs != NULL) {
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
mutex_exit(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rndsource_to_user_est(rs, &estat->source[i++]);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
mutex_enter(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rs = LIST_NEXT(rs, list);
}
KASSERT(i <= estat->count);
estat->count = i;
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
rnd_unlock_sources();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDGETSRCNAME: { /* Get entropy sources by name. */
rndstat_name_t *nstat = data;
const size_t n = sizeof(rs->name);
CTASSERT(sizeof(rs->name) == sizeof(nstat->name));
/*
* Under the lock, search by name. If found, copy it
* out; if not found, fail with ENOENT.
*/
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = rnd_lock_sources(ENTROPY_WAIT|ENTROPY_SIG);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (error) {
mutex_exit(&E->lock);
return error;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_FOREACH(rs, &E->sources, list) {
if (strncmp(rs->name, nstat->name, n) == 0)
break;
}
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (rs != NULL) {
mutex_exit(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rndsource_to_user(rs, &nstat->source);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
mutex_enter(&E->lock);
} else {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
error = ENOENT;
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
}
rnd_unlock_sources();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDGETESTNAME: { /* Get sources and estimates by name. */
rndstat_est_name_t *enstat = data;
const size_t n = sizeof(rs->name);
CTASSERT(sizeof(rs->name) == sizeof(enstat->name));
/*
* Under the lock, search by name. If found, copy it
* out; if not found, fail with ENOENT.
*/
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = rnd_lock_sources(ENTROPY_WAIT|ENTROPY_SIG);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (error) {
mutex_exit(&E->lock);
return error;
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
LIST_FOREACH(rs, &E->sources, list) {
if (strncmp(rs->name, enstat->name, n) == 0)
break;
}
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
if (rs != NULL) {
mutex_exit(&E->lock);
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rndsource_to_user_est(rs, &enstat->source);
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
mutex_enter(&E->lock);
} else {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
error = ENOENT;
Lock the rndsource list without E->lock for ioctls too. Use the same mechanism as entropy_request, with a little more diagnostic information in case anything goes wrong. No need for LIST_FOREACH_SAFE; elements cannot be deleted while the list is locked. This is part II of avoiding percpu_foreach with spin lock held.
2020-04-30 19:50:00 +03:00
}
rnd_unlock_sources();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_exit(&E->lock);
break;
}
case RNDCTL: { /* Modify entropy source flags. */
rndctl_t *rndctl = data;
const size_t n = sizeof(rs->name);
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
uint32_t resetflags = RND_FLAG_NO_ESTIMATE|RND_FLAG_NO_COLLECT;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
uint32_t flags;
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
bool reset = false, request = false;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
CTASSERT(sizeof(rs->name) == sizeof(rndctl->name));
/* Whitelist the flags that user can change. */
rndctl->mask &= RND_FLAG_NO_ESTIMATE|RND_FLAG_NO_COLLECT;
/*
* For each matching rndsource, either by type if
* specified or by name if not, set the masked flags.
*/
mutex_enter(&E->lock);
LIST_FOREACH(rs, &E->sources, list) {
if (rndctl->type != 0xff) {
if (rs->type != rndctl->type)
continue;
entropy(9): Allow changing flags on all entropy sources at once. Entropy sources should all have nonempty names, and this will enable an operator to, for example, disable all but a specific entropy source. XXX pullup-10
2023-03-03 15:52:49 +03:00
} else if (rndctl->name[0] != '\0') {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
if (strncmp(rs->name, rndctl->name, n) != 0)
continue;
}
flags = rs->flags & ~rndctl->mask;
flags |= rndctl->flags & rndctl->mask;
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
if ((rs->flags & resetflags) == 0 &&
(flags & resetflags) != 0)
reset = true;
if ((rs->flags ^ flags) & resetflags)
request = true;
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
atomic_store_relaxed(&rs->flags, flags);
}
mutex_exit(&E->lock);
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
/*
* If we disabled estimation or collection, nix all the
* pending entropy and set needed to the maximum.
*/
if (reset) {
xc_broadcast(0, &entropy_reset_xc, NULL, NULL);
mutex_enter(&E->lock);
entropy(9): Reintroduce netbsd<=9 time-delta estimator for unblocking. The system will (in a subsequent change) by default block for this condition before almost all of userland is running (including /etc/rc.d/sshd key generation). That way, a never-blocking getentropy(3) API will never return any data without at least best-effort entropy like netbsd<=9 did to applications except in single-user mode (where you have to be careful about everything anyway) or in the few processes that run before a seed can even be loaded (where blocking indefinitely, e.g. when generating a stack protector cookie in libc, could pose a severe availability problem that can't be configured away, but where the security impact is low). However, (in another subsequent change) we will continue to use _only_ HWRNG driver estimates and seed estimates, and _not_ time-delta estimator, for _warning_ about security in motd, daily security report, etc. And if HWRNG/seed provides enough entropy before time-delta estimator does, that will unblock /dev/random too. The result is: - Machines with HWRNG or seed won't warn about entropy and will essentially never block -- even on first boot without a seed, it will take only as long as the fastest HWRNG to unblock. - Machines with neither HWRNG nor seed: . will warn about entropy, giving feedback about security; and . will avoid returning anything more predictable than netbsd<=9; but . won't block (much) longer than netbsd<=9 would (and won't block again after blocking once, except with kern.entropy.depletion=1 for testing). (The threshold for unblocking is now somewhat higher than before: 512 samples that pass the time-delta estimator, rather than 80 as it used to be.) And, of course, adding a seed (or HWRNG) will prevent both warnings and blocking. The mechanism is: 1. /dev/random will block until _either_ (a) enough bits of entropy (256) from reliable sources have been added to the pool, _or_ (b) enough samples have been added from any sources (512), passing the old time-delta entropy estimator, that the possible security benefit doesn't justify holding up availability any longer (`best effort'), except on systems with higher security requirements like securelevel=2 which can disable non-HWRNG, non-seed sources with rndctl_flags in rc.conf(5). 2. dmesg will report `entropy: ready' when 1(a) is satisfied, but if 1(b) is satisfied first, it will report `entropy: best effort', so the concise log messages will reflect the timing and whether in any period of time any of the system might be relying on best effort entropy. 3. The sysctl knob kern.entropy.needed (and the ioctl RNDGETPOOLSTAT variable rndpoolstat_t::added) still reflects the number of bits of entropy from reliable sources, so we can still use this to suggest regenerating ssh keys. This matters on platforms that can only be reached, after flashing an installation image, by sshing in over a (private) network, like small network appliances or remote virtual machines without (interactive) serial consoles. If we blocked indefinitely at boot when generating ssh keys, such platforms would be unusable. This way, platforms are usable, but operators can still be advised at login time to regenerate keys as soon as they can actually load entropy onto the system, e.g. with rndctl(8) on a seed file copied from a local machine over the (private) network. 4. On machines without HWRNG, using a seed file still suppresses warnings for users who need more confident security. But it is no longer necessary for availability. This is a compromise between availability and security: - The security mechanism of blocking indefinitely on machines without HWRNG hurts availability too much, as painful experience over the multiple years since I made the mistake of introducing it have shown. (Sorry!) - The other main alternative, not having a blocking path at all (as I pushed for, and as OpenBSD has done for a long time) could potentially reduce security vs netbsd<=9, and would run against the expectations set by many popular operating systems to the severe detriment of public perception of NetBSD security. Even though we can't _confidently_ assess enough entropy from, e.g., sampling interrupt timings, this is the traditional behaviour that most operating systems provide -- and the result here is a net nondecrease in security over netbsd<=9, because all paths from the entropy pool to userland now have at least as high a standard before returning data as they did in netbsd<=9. PR kern/55641 PR pkg/55847 PR kern/57185 https://mail-index.netbsd.org/current-users/2020/09/02/msg039470.html https://mail-index.netbsd.org/current-users/2020/11/21/msg039931.html https://mail-index.netbsd.org/current-users/2020/12/05/msg040019.html XXX pullup-10
2023-07-01 00:42:05 +03:00
E->bitspending = 0;
E->samplespending = 0;
atomic_store_relaxed(&E->bitsneeded, MINENTROPYBITS);
atomic_store_relaxed(&E->samplesneeded, MINSAMPLES);
entropy(9): On flags change, cancel any scheduled consolidation. We've been instructed to lose confidence in existing entropy sources, so let's make sure to re-gather enough entropy before the next consolidation can happen, in case some of what would be counted in consolidation is from those entropy sources. XXX pullup-10
2023-05-24 23:22:12 +03:00
E->consolidate = false;
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
mutex_exit(&E->lock);
}
/*
* If we changed any of the estimation or collection
* flags, request new samples from everyone -- either
* to make up for what we just lost, or to get new
* samples from what we just added.
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
*
* Failing on signal, while waiting for another process
* to finish requesting entropy, is OK here even though
* we have committed side effects, because this ioctl
* command is idempotent, so repeating it is safe.
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
*/
if (request) {
mutex_enter(&E->lock);
entropy(9): Fix premature optimization deadlock in entropy_request. - For synchronous queries from /dev/random, which are waiting for entropy to be ready, wait for concurrent access -- e.g., concurrent rnd_detach_source -- to finish, and make sure to request entropy from all sources (unless we're interrupted by a signal). - When invoked through softint context (e.g., cprng_fast_intr -> cprng_strong -> entropy_extract), don't wait, because we're forbidden from waiting anyway. - For entropy_bootrequest, wait but don't bother failing on signal because this only happens in kthread context, not in userland process context, so there can't be signals. Nix rnd_trylock_sources; use the same entropy_extract flags (ENTROPY_WAIT, ENTROPY_SIG) for rnd_lock_sources.
2022-03-20 17:30:56 +03:00
error = entropy_request(ENTROPY_CAPACITY,
ENTROPY_WAIT|ENTROPY_SIG);
Make rndctl -E/-C reset entropy accounting. If we don't trust a source, it's unreasonable to trust any entropy it previously provided, and we don't have any way to undo only the effects of that source, so just zero our estimate of the entropy in the pool and start over. (However, keep the samples already in the pool -- just treat them as though they had zero entropy and start gathering more.)
2020-05-10 05:56:12 +03:00
mutex_exit(&E->lock);
}
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
break;
}
case RNDADDDATA: { /* Enter seed into entropy pool. */
rnddata_t *rdata = data;
unsigned entropybits = 0;
if (!atomic_load_relaxed(&entropy_collection))
break; /* thanks but no thanks */
if (rdata->len > MIN(sizeof(rdata->data), UINT32_MAX/NBBY))
return EINVAL;
/*
* This ioctl serves as the userland alternative a
* bootloader-provided seed -- typically furnished by
* /etc/rc.d/random_seed. We accept the user's entropy
* claim only if
*
* (a) the user is privileged, and
* (b) we have not entered a bootloader seed.
*
* under the assumption that the user may use this to
* load a seed from disk that we have already loaded
* from the bootloader, so we don't double-count it.
*/
Don't reject seed file entropy estimates, until one is nonzero. We try to avoid counting the seed file's entropy twice, e.g. once from the boot loader and once from rndctl via /etc/rc.d/random_seed. But previously, if you had a /var/db/entropy-file that was deemed to have zero entropy, that would prevent rndctl -L from _ever_ setting a nonzero entropy estimate, even if you (say) copy a seed file over from another machine (over a non-eavesdroppable medium) and try to load it in with rndctl -L, e.g. via `/etc/rc.d/random_seed start'. Now we accept the first _nonzero_ entropy estimate from a seed file. The operator can still always trick the kernel into believing there's entropy in the system by writing data to /dev/random, if the operator knows something the kernel doesn't; this only affects the _automated_ seed file loading.
2020-05-06 21:31:05 +03:00
if (privileged && rdata->entropy && rdata->len) {
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
mutex_enter(&E->lock);
if (!E->seeded) {
entropybits = MIN(rdata->entropy,
MIN(rdata->len, ENTROPY_CAPACITY)*NBBY);
E->seeded = true;
}
mutex_exit(&E->lock);
}
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
/* Enter the data and consolidate entropy. */
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
rnd_add_data(&seed_rndsource, rdata->data, rdata->len,
entropybits);
Consolidate entropy on RNDADDDATA and writes to /dev/random. The man page for some time has advertised: Writing to either /dev/random or /dev/urandom influences subsequent output of both devices, guaranteed to take effect at next open. So let's make that true again. It is a conscious choice _not_ to consolidate entropy frequently. For example, if you have a _slow_ HWRNG, which provides 32 bits of entropy every few seconds, and you reveal a hash that to the adversary before any more comes in, the adversary can in principle just keep guessing the intermediate state by a brute force search over ~2^32 possibilities. To mitigate this, the kernel generally tries to avoid consolidating entropy from the per-CPU pools until doing so would bring us from zero entropy to full entropy. However, there are various _possible_ sources of entropy which are just hard to give honest estimates for that are valid on ~all machines -- like interrupt timings. The time at which we read a seed in, which usually happens via /etc/rc.d/random_seed early in userland, is a reasonable time to gather this up. An operator or system engineer who knows another opportune moment can always issue `sysctl -w kern.entropy.consolidate=1'. Prompted by a suggestion from nia@ to consolidate entropy at the first transition to userland. I chose not to do that because it would likely cause warning fatigue on systems that are perfectly fine with a random seed -- doing it this way instead lets rndctl -L trigger the consolidation automatically. A subsequent commit will reorder the operations in rndctl again to make it work out better.
2020-05-07 22:05:51 +03:00
entropy_consolidate();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
break;
}
default:
error = ENOTTY;
}
/* Return any error that may have come up. */
return error;
}
/* Legacy entry points */
void
rnd_seed(void *seed, size_t len)
{
if (len != sizeof(rndsave_t)) {
printf("entropy: invalid seed length: %zu,"
" expected sizeof(rndsave_t) = %zu\n",
len, sizeof(rndsave_t));
return;
}
entropy_seed(seed);
}
void
rnd_init(void)
{
entropy_init();
}
void
rnd_init_softint(void)
{
entropy_init_late();
entropy(9): Request entropy after the softint is enabled. Otherwise, there is a window during which interrupts are running, but the softint is not, so if many interrupts queue (low-entropy) samples early at boot, they might get dropped on the floor. This could happen, for instance, with a PCI RNG like ubsec(4) or hifn(4) which requests entropy and processes it in its own hard interrupt handler.
2022-03-19 02:35:07 +03:00
entropy_bootrequest();
Rewrite entropy subsystem. Primary goals: 1. Use cryptography primitives designed and vetted by cryptographers. 2. Be honest about entropy estimation. 3. Propagate full entropy as soon as possible. 4. Simplify the APIs. 5. Reduce overhead of rnd_add_data and cprng_strong. 6. Reduce side channels of HWRNG data and human input sources. 7. Improve visibility of operation with sysctl and event counters. Caveat: rngtest is no longer used generically for RND_TYPE_RNG rndsources. Hardware RNG devices should have hardware-specific health tests. For example, checking for two repeated 256-bit outputs works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are necessarily designed to produce exactly uniform output. ENTROPY POOL - A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1 kludge as the cryptographic primitive. - `Entropy depletion' is available for testing purposes with a sysctl knob kern.entropy.depletion; otherwise it is disabled, and once the system reaches full entropy it is assumed to stay there as far as modern cryptography is concerned. - No `entropy estimation' based on sample values. Such `entropy estimation' is a contradiction in terms, dishonest to users, and a potential source of side channels. It is the responsibility of the driver author to study the entropy of the process that generates the samples. - Per-CPU gathering pools avoid contention on a global queue. - Entropy is occasionally consolidated into global pool -- as soon as it's ready, if we've never reached full entropy, and with a rate limit afterward. Operators can force consolidation now by running sysctl -w kern.entropy.consolidate=1. - rndsink(9) API has been replaced by an epoch counter which changes whenever entropy is consolidated into the global pool. . Usage: Cache entropy_epoch() when you seed. If entropy_epoch() has changed when you're about to use whatever you seeded, reseed. . Epoch is never zero, so initialize cache to 0 if you want to reseed on first use. . Epoch is -1 iff we have never reached full entropy -- in other words, the old rnd_initial_entropy is (entropy_epoch() != -1) -- but it is better if you check for changes rather than for -1, so that if the system estimated its own entropy incorrectly, entropy consolidation has the opportunity to prevent future compromise. - Sysctls and event counters provide operator visibility into what's happening: . kern.entropy.needed - bits of entropy short of full entropy . kern.entropy.pending - bits known to be pending in per-CPU pools, can be consolidated with sysctl -w kern.entropy.consolidate=1 . kern.entropy.epoch - number of times consolidation has happened, never 0, and -1 iff we have never reached full entropy CPRNG_STRONG - A cprng_strong instance is now a collection of per-CPU NIST Hash_DRBGs. There are only two in the system: user_cprng for /dev/urandom and sysctl kern.?random, and kern_cprng for kernel users which may need to operate in interrupt context up to IPL_VM. (Calling cprng_strong in interrupt context does not strike me as a particularly good idea, so I added an event counter to see whether anything actually does.) - Event counters provide operator visibility into when reseeding happens. INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG) - Unwired for now; will be rewired in a subsequent commit.
2020-04-30 06:28:18 +03:00
}
int
rnd_system_ioctl(struct file *fp, unsigned long cmd, void *data)
{
return entropy_ioctl(cmd, data);
}