s390/purgatory: Do not use fortified string functions
With the addition of -fstrict-flex-arrays=3, struct sha256_state's trailing array is no longer ignored by CONFIG_FORTIFY_SOURCE: struct sha256_state { u32 state[SHA256_DIGEST_SIZE / 4]; u64 count; u8 buf[SHA256_BLOCK_SIZE]; }; This means that the memcpy() calls with "buf" as a destination in sha256.c's code will attempt to perform run-time bounds checking, which could lead to calling missing functions, specifically a potential WARN_ONCE, which isn't callable from purgatory. Reported-by: Thorsten Leemhuis <linux@leemhuis.info> Closes: https://lore.kernel.org/lkml/175578ec-9dec-7a9c-8d3a-43f24ff86b92@leemhuis.info/Bisected-by: "Joan Bruguera Micó" <joanbrugueram@gmail.com> Fixes: df8fc4e9 ("kbuild: Enable -fstrict-flex-arrays=3") Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Linux Kernel Functional Testing <lkft@linaro.org> Cc: Nathan Chancellor <nathan@kernel.org> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: linux-s390@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Link: https://lore.kernel.org/r/20230531003414.never.050-kees@kernel.org
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