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

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Jun 30, 2025 at 08:26:34AM +0200, Ingo Franzki wrote:
> On 27.06.2025 20:56, 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; 
> 
> The NIP flag is only recognized by the SHA3 function codes if the KIMD instruction, for the others (SHA1 and SHA2) it is ignored.
> 

Ah, that explains it then.

> > 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")
> 
> If this patch is applied on 88c02b3f79a6 then the first_message_part field should
> probably set to 0 instead of false, since only since commit 
> 7b83638f962c30cb6271b5698dc52cdf9b638b48 "crypto: s390/sha1 - Use API partial block handling"
> first_message_part is a bool, before it was an int. 

Yes, when backporting this patch to 6.15 and 6.12 there will be 2 things that
I'll change:

1. Extend it to cover SHA-224 and SHA-256 (which had been reworked in 6.16)
2. Change false to 0

- Eric