And the associated ezload EZ-USB code, which is only used by uyap.
It could theoretically be used by other drivers, but none of them are
in tree.
I suspect that this device isn't in use, as phone technology has improved
a lot since 2001 when uyap(4) was added to the tree.
Proposed with no objections on netbsd-users on 13 April 2020
It is simpler if there is only one place we check the condition.
That said, there are cases where the caller needs to re-check before
choosing to fail (e.g., futex_wait in kern/sys_futex.c, which must
verify the condition before taking destructive steps to abort the
wait). But it's not clear that that's the norm.
Previously, a negative timeout was forbidden (kassert), a zero or
maybe even just a sufficiently small timeout would block forever, and
we would subtract the time elapsed -- possibly longer than the
timeout, leading to a negative updated timeout, which would trip the
kassert the next time around if used as advertised. DERP.
Now negative timeouts are still forbidden in order to detect usage
mistakes, but a zero timeout fails immediately and we clamp the
subtracted time to be at least zero so you can always safely call
cv_timedwaitbt in a loop.
(An alternative would be to fail immediately for all nonpositive
timeouts, and to leave in the timespec the negative time we overshot,
but it's not clear this would be useful.)
This way the first two paragraphs have parallel structure:
- _Applications_ should read from /dev/urandom or sysctl kern.arandom...
- _Systems_ should be engineered to read once from /dev/random...
Primary goals:
1. Use cryptography primitives designed and vetted by cryptographers.
2. Be honest about entropy estimation.
3. Propagate full entropy as soon as possible.
4. Simplify the APIs.
5. Reduce overhead of rnd_add_data and cprng_strong.
6. Reduce side channels of HWRNG data and human input sources.
7. Improve visibility of operation with sysctl and event counters.
Caveat: rngtest is no longer used generically for RND_TYPE_RNG
rndsources. Hardware RNG devices should have hardware-specific
health tests. For example, checking for two repeated 256-bit outputs
works to detect AMD's 2019 RDRAND bug. Not all hardware RNGs are
necessarily designed to produce exactly uniform output.
ENTROPY POOL
- A Keccak sponge, with test vectors, replaces the old LFSR/SHA-1
kludge as the cryptographic primitive.
- `Entropy depletion' is available for testing purposes with a sysctl
knob kern.entropy.depletion; otherwise it is disabled, and once the
system reaches full entropy it is assumed to stay there as far as
modern cryptography is concerned.
- No `entropy estimation' based on sample values. Such `entropy
estimation' is a contradiction in terms, dishonest to users, and a
potential source of side channels. It is the responsibility of the
driver author to study the entropy of the process that generates
the samples.
- Per-CPU gathering pools avoid contention on a global queue.
- Entropy is occasionally consolidated into global pool -- as soon as
it's ready, if we've never reached full entropy, and with a rate
limit afterward. Operators can force consolidation now by running
sysctl -w kern.entropy.consolidate=1.
- rndsink(9) API has been replaced by an epoch counter which changes
whenever entropy is consolidated into the global pool.
. Usage: Cache entropy_epoch() when you seed. If entropy_epoch()
has changed when you're about to use whatever you seeded, reseed.
. Epoch is never zero, so initialize cache to 0 if you want to reseed
on first use.
. Epoch is -1 iff we have never reached full entropy -- in other
words, the old rnd_initial_entropy is (entropy_epoch() != -1) --
but it is better if you check for changes rather than for -1, so
that if the system estimated its own entropy incorrectly, entropy
consolidation has the opportunity to prevent future compromise.
- Sysctls and event counters provide operator visibility into what's
happening:
. kern.entropy.needed - bits of entropy short of full entropy
. kern.entropy.pending - bits known to be pending in per-CPU pools,
can be consolidated with sysctl -w kern.entropy.consolidate=1
. kern.entropy.epoch - number of times consolidation has happened,
never 0, and -1 iff we have never reached full entropy
CPRNG_STRONG
- A cprng_strong instance is now a collection of per-CPU NIST
Hash_DRBGs. There are only two in the system: user_cprng for
/dev/urandom and sysctl kern.?random, and kern_cprng for kernel
users which may need to operate in interrupt context up to IPL_VM.
(Calling cprng_strong in interrupt context does not strike me as a
particularly good idea, so I added an event counter to see whether
anything actually does.)
- Event counters provide operator visibility into when reseeding
happens.
INTEL RDRAND/RDSEED, VIA C3 RNG (CPU_RNG)
- Unwired for now; will be rewired in a subsequent commit.
