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We're seeing periodic reports of errors like:
$ qemu-img create -f luks --object secret,data=123456,id=sec0 \
-o key-secret=sec0 luks-info.img 1M
Formatting 'luks-info.img', fmt=luks size=1048576 key-secret=sec0
qemu-img: luks-info.img: Unable to get accurate CPU usage
This error message comes from a recent attempt to workaround a
kernel bug with measuring rusage in long running processes:
commit c72cab5ad9f849bbcfcf4be7952b8b8946cc626e
Author: Tiago Pasqualini <tiago.pasqualini@canonical.com>
Date: Wed Sep 4 20:52:30 2024 -0300
crypto: run qcrypto_pbkdf2_count_iters in a new thread
Unfortunately this has a subtle bug on machines which are very fast.
On the first time around the loop, the 'iterations' value is quite
small (1 << 15), and so will run quite fast. Testing has shown that
some machines can complete this benchmarking task in as little as
7 milliseconds.
Unfortunately the 'getrusage' data is not updated at the time of
the 'getrusage' call, it is done asynchronously by the scheduler.
The 7 millisecond completion time for the benchmark is short
enough that 'getrusage' sometimes reports 0 accumulated execution
time.
As a result the 'delay_ms == 0' sanity check in the above commit
is triggering non-deterministically on such machines.
The benchmarking loop intended to run multiple times, increasing
the 'iterations' value until the benchmark ran for > 500 ms, but
the sanity check doesn't allow this to happen.
To fix it, we keep a loop counter and only run the sanity check
after we've been around the loop more than 5 times. At that point
the 'iterations' value is high enough that even with infrequent
updates of 'getrusage' accounting data on fast machines, we should
see a non-zero value.
Fixes: https://lore.kernel.org/qemu-devel/ffe542bb-310c-4616-b0ca-13182f849fd1@redhat.com/
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2336437
Reported-by: Thomas Huth <thuth@redhat.com>
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250109093746.1216300-1-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
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QAPI's 'prefix' feature can make the connection between enumeration
type and its constants less than obvious. It's best used with
restraint.
QCryptoHashAlgorithm has a 'prefix' that overrides the generated
enumeration constants' prefix to QCRYPTO_HASH_ALG.
We could simply drop 'prefix', but then the prefix becomes
QCRYPTO_HASH_ALGORITHM, which is rather long.
We could additionally rename the type to QCryptoHashAlg, but I think
the abbreviation "alg" is less than clear.
Rename the type to QCryptoHashAlgo instead. The prefix becomes to
QCRYPTO_HASH_ALGO.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20240904111836.3273842-12-armbru@redhat.com>
[Conflicts with merge commit 7bbadc60b58b resolved]
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CPU time accounting in the kernel has been demonstrated to have a
sawtooth pattern[1][2]. This can cause the getrusage system call to
not be as accurate as we are expecting, which can cause this calculation
to stall.
The kernel discussions shows that this inaccuracy happens when CPU time
gets big enough, so this patch changes qcrypto_pbkdf2_count_iters to run
in a fresh thread to avoid this inaccuracy. It also adds a sanity check
to fail the process if CPU time is not accounted.
[1] https://lore.kernel.org/lkml/159231011694.16989.16351419333851309713.tip-bot2@tip-bot2/
[2] https://lore.kernel.org/lkml/20221226031010.4079885-1-maxing.lan@bytedance.com/t/#m1c7f2fdc0ea742776a70fd1aa2a2e414c437f534
Resolves: #2398
Signed-off-by: Tiago Pasqualini <tiago.pasqualini@canonical.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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When the user creates a LUKS-encrypted qcow2 image using the qemu-img
program, the passphrase is hashed using PBKDF2 with a dynamic
number of iterations. The number of iterations is determined by
measuring thread cpu time usage, such that it takes approximately
2 seconds to compute the hash.
Because Darwin doesn't implement getrusage(RUSAGE_THREAD), we get an
error message:
> qemu-img: test.qcow2: Unable to calculate thread CPU usage on this platform
for this command:
> qemu-img create --object secret,id=key,data=1234 -f qcow2 -o 'encrypt.format=luks,encrypt.key-secret=key' test.qcow2 100M
This patch implements qcrypto_pbkdf2_get_thread_cpu() for Darwin so that
the above command works.
Signed-off-by: Jungmin Park <pjm0616@gmail.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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Simplify cleanup paths by using glib's auto cleanup macros for stack
variables, allowing several goto jumps / labels to be eliminated.
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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It's either "GNU *Library* General Public License version 2" or "GNU
Lesser General Public License version *2.1*", but there was no "version
2.0" of the "Lesser" license. So assume that version 2.1 is meant here.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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Currently when timing the pbkdf algorithm a fixed key
size of 32 bytes is used. This results in inaccurate
timings for certain hashes depending on their digest
size. For example when using sha1 with aes-256, this
causes us to measure time for the master key digest
doing 2 sha1 operations per iteration, instead of 1.
Instead we should pass in the desired key size to the
timing routine that matches the key size that will be
used for real later.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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The 'out' buffer will hold a key derived from master
password, so it is best practice to clear this buffer
when no longer required.
At this time, the code isn't worrying about locking
buffers into RAM to prevent swapping sensitive data
to disk.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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The qcrypto_pbkdf_count_iters method uses a 64 bit int
but then checks its value against INT32_MAX before
returning it. This bounds check is premature, because
the calling code may well scale the iteration count
by some value. It is thus better to return a 64-bit
integer and let the caller do range checking.
For consistency the qcrypto_pbkdf method is also changed
to accept a 64bit int, though this is somewhat academic
since nettle is limited to taking an 'int' while gcrypt
is limited to taking a 'long int'.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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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>
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The LUKS data format includes use of PBKDF2 (Password-Based
Key Derivation Function). The Nettle library can provide
an implementation of this, but we don't want code directly
depending on a specific crypto library backend. Introduce
a new include/crypto/pbkdf.h header which defines a QEMU
API for invoking PBKDK2. The initial implementations are
backed by nettle & gcrypt, which are commonly available
with distros shipping GNUTLS.
The test suite data is taken from the cryptsetup codebase
under the LGPLv2.1+ license. This merely aims to verify
that whatever backend we provide for this function in QEMU
will comply with the spec.
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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