[PATCH 0/7] arm: crypto: sha256: fix generation of thumb2 assembly

Thu Nov 7 06:03:43 PST 2024

Hi Ahmad,

On 07.11.24 10:19, Ahmad Fatoum wrote:
> Hello Stefan,
> 
> On 07.11.24 10:12, Stefan Kerkmann wrote:
>> Hi Sascha,
>>
>> On 06.11.24 17:34, Stefan Kerkmann wrote:
>>> The checked in `sha256-core.S_shipped` assembly file has a thumb2
>>> specific workaround applied[1]. This fix wasn't backported to the perl
>>> script `sha256-armv4.pl` used to generate the assembly, thus when the
>>> script is run it would regenerate the buggy code.
>>>
>>> In-tree builds were not affected as the assembly file already exists in
>>> the source tree. However in the context of an out-of-tree build (make
>>> O=xyz) the file isn't present from the pov of make - triggering a
>>> regeneration. This happens by default during Yocto builds - leading to a
>>> broken sha256 sum function on ARMv7 compiled with Thumb2 support. The
>>> bug expresses itself not in crashes but wrong sha256 sums.
>>
>> I just (re-)tested this part without the patch applied, and I'm unable to
>> reproduce it in a cleanly checked out state of my BSP. The full chain of events
>> and conditions that lead to the regeneration of the file is thus not fully
>> understood (yet) — but it clearly happened for me.
> 
> Try manually touching arch/arch/crypto/sha256-armv4.pl, so it's more
> recent than sha256-core.S_shipped. The modification timestamps after a
> git checkout order are non-deterministic and that's probably what bites you.
> 

That did the trick! I updated the commit messages in the v2 series. Thanks for
the insight :-).

> The kernel used to consult an environment variable to determine whether
> to rebuild the shipped files exactly to avoid this.
> 
> In recent kernel versions, this has been replaced by unconditionally
> running the Perl script. I don't know what's the reason behind that.
> 
> Cheers,
> Ahmad
> 

Cheers,
Stefan

>>
>> Here is the output of a CI[1] run with the assembly file (forcefully) generated
>> from the script, that shoes the errors I ran into:
>>
>>   test_digests_sha12:153: mismatch calculating sha224-asm(zeroes7):
>>   	got: c56f57826fa8cc1cae10a3450b90162677ba55cdbaa3d2a72810853e
>>   	but: fbf6df85218ac5632461a8a17c6f294e6f35264cbfc0a9774a4f665b expected
>>   test_digests_sha12:153: mismatch calculating sha224-asm(one32):
>>   	got: 3a81d42a638cf434f5b002ead1252be963880bd3eec627a8b3278bb4
>>   	but: 343cb3950305e6e6331e294b0a4925739d09ecbd2b43a2fc87c09941 expected
>>   test_digests_sha12:153: mismatch calculating sha224-asm(inc4097):
>>   	got: 2e6565a91ff0e4f0d316067ad66eaa3b76d71317171adfd0ec6bbcd4
>>   	but: 6596b5dcfbd857f4246d6b94508b8a1a5b715a4f644a0c1e7d54c4f7 expected
>>   test_digests_sha12:164: mismatch calculating sha256-asm(zeroes7):
>>   	got: 71ab8ff93158c3b8863460dac03e9049bd5d3ec1a2ec4a1ba6e434d0fd33eb5f
>>   	but: 837885c8f8091aeaeb9ec3c3f85a6ff470a415e610b8ba3e49f9b33c9cf9d619 expected
>>   test_digests_sha12:164: mismatch calculating sha256-asm(one32):
>>   	got: bcbd77ba0128aed7df96f75788fefa5e8da2501bfd3e0fe14753d4b5c27b1564
>>   	but: 01d0fabd251fcbbe2b93b4b927b26ad2a1a99077152e45ded1e678afa45dbec5 expected
>>   test_digests_sha12:164: mismatch calculating sha256-asm(inc4097):
>>   	got: 4dd697b3bf8f7f0630b583356d48dcc7a1c345e62fe189c1d4843a38cd7d59a9
>>   	but: 1e973d029df2b2c66cb42a942c5edb45966f02abaff29fe99410e44d271d0efc expected
>>   test_digests_sha12:153: mismatch calculating sha224(zeroes7):
>>   	got: c56f57826fa8cc1cae10a3450b90162677ba55cdbaa3d2a72810853e
>>   	but: fbf6df85218ac5632461a8a17c6f294e6f35264cbfc0a9774a4f665b expected
>>   test_digests_sha12:153: mismatch calculating sha224(one32):
>>   	got: 3a81d42a638cf434f5b002ead1252be963880bd3eec627a8b3278bb4
>>   	but: 343cb3950305e6e6331e294b0a4925739d09ecbd2b43a2fc87c09941 expected
>>   test_digests_sha12:153: mismatch calculating sha224(inc4097):
>>   	got: 2e6565a91ff0e4f0d316067ad66eaa3b76d71317171adfd0ec6bbcd4
>>   	but: 6596b5dcfbd857f4246d6b94508b8a1a5b715a4f644a0c1e7d54c4f7 expected
>>   test_digests_sha12:164: mismatch calculating sha256(zeroes7):
>>   	got: 71ab8ff93158c3b8863460dac03e9049bd5d3ec1a2ec4a1ba6e434d0fd33eb5f
>>   	but: 837885c8f8091aeaeb9ec3c3f85a6ff470a415e610b8ba3e49f9b33c9cf9d619 expected
>>   test_digests_sha12:164: mismatch calculating sha256(one32):
>>   	got: bcbd77ba0128aed7df96f75788fefa5e8da2501bfd3e0fe14753d4b5c27b1564
>>   	but: 01d0fabd251fcbbe2b93b4b927b26ad2a1a99077152e45ded1e678afa45dbec5 expected
>>   test_digests_sha12:164: mismatch calculating sha256(inc4097):
>>   	got: 4dd697b3bf8f7f0630b583356d48dcc7a1c345e62fe189c1d4843a38cd7d59a9
>>   	but: 1e973d029df2b2c66cb42a942c5edb45966f02abaff29fe99410e44d271d0efc expected
>>   ERROR: digest: failed 12 out of 45 tests
>>
>> [1]: https://github.com/KarlK90/barebox/actions/runs/11704376345/job/32596699159
>>
>>
>> So the patch is still valid, but this paragraph should be replaced with:
>>
>> Under rare circumstances, in my case it was a Yocto build of barebox from an
>> external source tree, the assembly file was regenerated. Leading to a broken
>> sha256 sum function on ARMv7 compiled with Thumb2 support. The bug expressed
>> itself not in crashes but wrong sha256 sums.
>>
>> Should I send a v2 for the updated message?
>>
>>> The mentioned problem in[1] was fixed and explained further in upstream
>>> commit[2]. Thus this series updates the script and generated assembly to
>>> the most recent Kernel commit[3].
>>>
>>> To better catch regressions in the future the existing digest tests now
>>> exercise the optimized implementations for ARMv5/v6/v7/v8 and the ARMv7
>>> test binaries are compiled in thumb2 mode.
>>>
>>> [1]: b73bc6e303 (arm: crypto: fix SHA256 shipped assembler code, 2018-10-05)
>>> [2]: 69216a545cf8 (crypto: sha256/arm - fix crash bug in Thumb2 build, 2019-02-16)
>>> [3]: 54781938ec34 (crypto: arm/sha256-neon - avoid ADRL pseudo instruction, 2020-09-16)
>>>
>>> Signed-off-by: Stefan Kerkmann <s.kerkmann at pengutronix.de>
>>> ---
>>> Stefan Kerkmann (7):
>>>       arm: crypto: sha256: fix generation of thumb2 assembly
>>>       arm: configs: multi_v5_v6_defconfig: move rpi1 armv6 targets
>>>       arm: configs: multi_v5_v6_defconfig: enable arm optimized sha1/sha256 digest
>>>       arm: configs: multi_v7_defconfig: compile for thumb2
>>>       arm: configs: multi_v7_defconfig: enable arm optimized sha256 digest
>>>       arm: configs: multi_v8_defconfig: enable arm optimized sha1/sha256 digest
>>>       test: arm: rpi: run tests against multi_v5_v6_defconfig
>>>
>>>  .github/workflows/test-labgrid-pytest.yml          |  4 ++
>>>  arch/arm/configs/multi_v5_v6_defconfig             |  6 ++-
>>>  arch/arm/configs/multi_v7_defconfig                |  7 +--
>>>  arch/arm/configs/multi_v8_defconfig                |  5 +-
>>>  arch/arm/crypto/sha256-armv4.pl                    | 25 ++++++----
>>>  arch/arm/crypto/sha256-core.S_shipped              | 55 ++++++++++++++++++----
>>>  ...yaml => qemu-raspi0 at multi_v5_v6_defconfig.yaml} |  0
>>>  ...ml => qemu-raspi1ap at multi_v5_v6_defconfig.yaml} |  0
>>>  8 files changed, 74 insertions(+), 28 deletions(-)
>>> ---
>>> base-commit: d9f7f6d930069df35e28fedb35719bfd12fbd6e4
>>> change-id: 20241106-fix-sha256-assembly-ad3d25bf5a9f
>>>
>>> Best regards,
>>
>> Cheers,
>> Stefan
>>
> 
> 

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