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Commit88c02b3f79("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 zero. 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:88c02b3f79("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> Link: https://lore.kernel.org/r/20250703172316.7914-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@kernel.org>