Re: [PATCH] crypto: s390/sha - Fix uninitialized variable in SHA-1 and SHA-2

Eric Biggers
2025-06-30T17:03:24Z

On Mon, Jun 30, 2025 at 09:58:05AM -0700, Eric Biggers wrote:
> On Fri, Jun 27, 2025 at 11:56:49AM -0700, Eric Biggers wrote:
> > Commit 88c02b3f79a6 ("s390/sha3: Support sha3 performance enhancements")
> > added the field s390_sha_ctx::first_message_part and made it be used by
> > s390_sha_update_blocks(). At the time, s390_sha_update_blocks() was
> > used by all the s390 SHA-1, SHA-2, and SHA-3 algorithms. However, only
> > the initialization functions for SHA-3 were updated, leaving SHA-1 and
> > SHA-2 using first_message_part uninitialized.
> >
> > This could cause e.g. CPACF_KIMD_SHA_512 | CPACF_KIMD_NIP to be used
> > instead of just CPACF_KIMD_NIP. It's unclear why this didn't cause a
> > problem earlier; this bug was found only when UBSAN detected the
> > uninitialized boolean. Perhaps the CPU ignores CPACF_KIMD_NIP for SHA-1
> > and SHA-2. Regardless, let's fix this. For now just initialize to
> > false, i.e. don't try to "optimize" the SHA state initialization.
> >
> > Note: in 6.16, we need to patch SHA-1, SHA-384, and SHA-512. In 6.15
> > and earlier, we'll also need to patch SHA-224 and SHA-256, as they
> > hadn't yet been librarified (which incidentally fixed this bug).
> >
> > Fixes: 88c02b3f79a6 ("s390/sha3: Support sha3 performance enhancements")
> > Cc: stable@vger.kernel.org
> > Reported-by: Ingo Franzki <ifranzki@linux.ibm.com>
> > Closes: https://lore.kernel.org/r/12740696-595c-4604-873e-aefe8b405fbf@linux.ibm.com
> > Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> > ---
> >
> > This is targeting 6.16. I'd prefer to take this through
> > libcrypto-fixes, since the librarification work is also touching this
> > area. But let me know if there's a preference for the crypto tree or
> > the s390 tree instead.
>
> Applied to https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=libcrypto-fixes

Forgot to mention: I revised the first two paragraphs of the commit message to
fix a couple things and clarify that the accidental CPACF_KIMD_NIP was indeed
ignored (as per Ingo):

crypto: s390/sha - Fix uninitialized variable in SHA-1 and SHA-2

Commit 88c02b3f79a6 ("s390/sha3: Support sha3 performance enhancements")
added the field s390_sha_ctx::first_message_part and made it be used by
s390_sha_update() (now s390_sha_update_blocks()). At the time,
s390_sha_update() was used by all the s390 SHA-1, SHA-2, and SHA-3
algorithms. However, only the initialization functions for SHA-3 were
updated, leaving SHA-1 and SHA-2 using first_message_part uninitialized.

This could cause e.g. the function code CPACF_KIMD_SHA_512 |
CPACF_KIMD_NIP to be used instead of just CPACF_KIMD_SHA_512. This
apparently was harmless, as the SHA-1 and SHA-2 function codes ignore
CPACF_KIMD_NIP; it is recognized only by the SHA-3 function codes
(https://lore.kernel.org/r/73477fe9-a1dc-4e38-98a6-eba9921e8afa@linux.ibm.com/).
Therefore, this bug was found only when first_message_part was later
converted to a boolean and UBSAN detected its uninitialized use.
Regardless, let's fix this by just initializing to false.

Note: in 6.16, we need to patch SHA-1, SHA-384, and SHA-512. In 6.15
and earlier, we'll also need to patch SHA-224 and SHA-256, as they
hadn't yet been librarified (which incidentally fixed this bug).

Fixes: 88c02b3f79a6 ("s390/sha3: Support sha3 performance enhancements")
Cc: stable@vger.kernel.org
Reported-by: Ingo Franzki <ifranzki@linux.ibm.com>
Closes: https://lore.kernel.org/r/12740696-595c-4604-873e-aefe8b405fbf@linux.ibm.com
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Link: https://lore.kernel.org/r/20250627185649.35321-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>