When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
source of entropy, and that source needs to be "non-blocking", like
`/dev/urandom`. However, currently QEMU defaults to the problematic
`/dev/random`, which on Linux is "blocking" (as in, it waits until
sufficient entropy is available).
Why prefer `/dev/urandom` over `/dev/random`?
---------------------------------------------
The man pages of urandom(4) and random(4) state:
"The /dev/random device is a legacy interface which dates back to a
time where the cryptographic primitives used in the implementation
of /dev/urandom were not widely trusted. It will return random
bytes only within the estimated number of bits of fresh noise in the
entropy pool, blocking if necessary. /dev/random is suitable for
applications that need high quality randomness, and can afford
indeterminate delays."
Further, the "Usage" section of the said man pages state:
"The /dev/random interface is considered a legacy interface, and
/dev/urandom is preferred and sufficient in all use cases, with the
exception of applications which require randomness during early boot
time; for these applications, getrandom(2) must be used instead,
because it will block until the entropy pool is initialized.
"If a seed file is saved across reboots as recommended below (all
major Linux distributions have done this since 2000 at least), the
output is cryptographically secure against attackers without local
root access as soon as it is reloaded in the boot sequence, and
perfectly adequate for network encryption session keys. Since reads
from /dev/random may block, users will usually want to open it in
nonblocking mode (or perform a read with timeout), and provide some
sort of user notification if the desired entropy is not immediately
available."
And refer to random(7) for a comparison of `/dev/random` and
`/dev/urandom`.
What about other OSes?
----------------------
`/dev/urandom` exists and works on OS-X, FreeBSD, DragonFlyBSD, NetBSD
and OpenBSD, which cover all the non-Linux platforms we explicitly
support, aside from Windows.
On Windows `/dev/random` doesn't work either so we don't regress.
This is actually another argument in favour of using the newly
proposed 'rng-builtin' backend by default, as that will work on
Windows.
- - -
Given the above, change the entropy source for VirtIO-RNG device to
`/dev/urandom`.
Related discussion in these[1][2] past threads.
[1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
-- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
[2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
-- "[RFC] Virtio RNG: Consider changing the default entropy source to
/dev/urandom"
Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20190529143106.11789-2-lvivier@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Usually, Random Number Generator is abbreviated to RNG/rng.
so replacing RndRandom with RngRandom seems more reasonable
and keep consistent with RngBackend.
Signed-off-by: Wei Jiangang <weijg.fnst@cn.fujitsu.com>
Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
Message-Id: <1460684168-5403-1-git-send-email-weijg.fnst@cn.fujitsu.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Commit 57cb38b included qapi/error.h into qemu/osdep.h to get the
Error typedef. Since then, we've moved to include qemu/osdep.h
everywhere. Its file comment explains: "To avoid getting into
possible circular include dependencies, this file should not include
any other QEMU headers, with the exceptions of config-host.h,
compiler.h, os-posix.h and os-win32.h, all of which are doing a
similar job to this file and are under similar constraints."
qapi/error.h doesn't do a similar job, and it doesn't adhere to
similar constraints: it includes qapi-types.h. That's in excess of
100KiB of crap most .c files don't actually need.
Add the typedef to qemu/typedefs.h, and include that instead of
qapi/error.h. Include qapi/error.h in .c files that need it and don't
get it now. Include qapi-types.h in qom/object.h for uint16List.
Update scripts/clean-includes accordingly. Update it further to match
reality: replace config.h by config-target.h, add sysemu/os-posix.h,
sysemu/os-win32.h. Update the list of includes in the qemu/osdep.h
comment quoted above similarly.
This reduces the number of objects depending on qapi/error.h from "all
of them" to less than a third. Unfortunately, the number depending on
qapi-types.h shrinks only a little. More work is needed for that one.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
[Fix compilation without the spice devel packages. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
QSIMPLEQ supports appending to tail in O(1) and is intrusive so
it doesn't require extra memory allocations for the bookkeeping
data.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Message-Id: <1457010971-24771-1-git-send-email-lprosek@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Requests are now created in the RngBackend parent class and the
code path is shared by both rng-egd and rng-random.
This commit fixes the rng-random implementation which processed
only one request at a time and simply discarded all but the most
recent one. In the guest this manifested as delayed completion
of reads from virtio-rng, i.e. a read was completed only after
another read was issued.
By switching rng-random to use the same request queue as rng-egd,
the unsafe stack-based allocation of the entropy buffer is
eliminated and replaced with g_malloc.
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Message-Id: <1456994238-9585-5-git-send-email-lprosek@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Clean up includes so that osdep.h is included first and headers
which it implies are not included manually.
This commit was created with scripts/clean-includes.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1454089805-5470-5-git-send-email-peter.maydell@linaro.org
These macros expand into error class enumeration constant, comma,
string. Unclean. Has been that way since commit 13f59ae.
The error class is always ERROR_CLASS_GENERIC_ERROR since the previous
commit.
Clean up as follows:
* Prepend every use of a QERR_ macro by ERROR_CLASS_GENERIC_ERROR, and
delete it from the QERR_ macro. No change after preprocessing.
* Rewrite error_set(ERROR_CLASS_GENERIC_ERROR, ...) into
error_setg(...). Again, no change after preprocessing.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
g_free() is NULL-safe.
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
The file descriptor is never initialized to -1, which makes rng-random
close stdin if an object is created and immediately destroyed. If we
change it to -1, we also need to protect qemu_set_fd_handler from
receiving a bogus file descriptor.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Not handling EAGAIN triggers the assert
qemu/backends/rng-random.c:44:entropy_available: assertion failed: (len != -1)
Aborted (core dumped)
This happens when starting a guest with '-device virtio-rng-pci',
issuing a 'cat /dev/hwrng' in the guest, while also doing 'cat
/dev/random' on the host.
Reported-by: yunpingzheng <yunzheng@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Message-id: eacda84dfaf2d99cf6d250b678be4e4d6c2088fb.1366108096.git.amit.shah@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
In the rng backend use qemu_open and qemu_close rather than POSIX
open/close.
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Since 39bffca203 (qdev: register all
types natively through QEMU Object Model), TypeInfo as used in
the common, non-iterative pattern is no longer amended with information
and should therefore be const.
Fix the documented QOM examples:
sed -i 's/static TypeInfo/static const TypeInfo/g' include/qom/object.h
Since frequently the wrong examples are being copied by contributors of
new devices, fix all types in the tree:
sed -i 's/^static TypeInfo/static const TypeInfo/g' */*.c
sed -i 's/^static TypeInfo/static const TypeInfo/g' */*/*.c
This also avoids to piggy-back these changes onto real functional
changes or other refactorings.
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
The filename can be overridden but it expects a non-blocking source of entropy.
A typical invocation would be:
qemu -object rng-random,id=rng0 -device virtio-rng-pci,rng=rng0
This can also be used with /dev/urandom by using the command line:
qemu -object rng-random,filename=/dev/urandom,id=rng0 \
-device virtio-rng-pci,rng=rng0
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
v1 -> v2
- merged header split patch into this one
v2 -> v3
- bug fix in rng-random (Paolo)
