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

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Message-ID: <20250630170245.GD1220@sol>
Date: Mon, 30 Jun 2025 10:02:45 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: linux-crypto@...r.kernel.org
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	Harald Freudenberger <freude@...ux.ibm.com>,
	Holger Dengler <dengler@...ux.ibm.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Joerg Schmidbauer <jschmidb@...ibm.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org,
	Ingo Franzki <ifranzki@...ux.ibm.com>
Subject: Re: [PATCH] crypto: s390/sha - Fix uninitialized variable in SHA-1
 and SHA-2

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@...r.kernel.org
> > Reported-by: Ingo Franzki <ifranzki@...ux.ibm.com>
> > Closes: https://lore.kernel.org/r/12740696-595c-4604-873e-aefe8b405fbf@linux.ibm.com
> > Signed-off-by: Eric Biggers <ebiggers@...nel.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@...r.kernel.org
    Reported-by: Ingo Franzki <ifranzki@...ux.ibm.com>
    Closes: https://lore.kernel.org/r/12740696-595c-4604-873e-aefe8b405fbf@linux.ibm.com
    Acked-by: Heiko Carstens <hca@...ux.ibm.com>
    Reviewed-by: Ingo Franzki <ifranzki@...ux.ibm.com>
    Link: https://lore.kernel.org/r/20250627185649.35321-1-ebiggers@kernel.org
    Signed-off-by: Eric Biggers <ebiggers@...nel.org>