lib/crypto: x86/sha256: Follow the normal %rbp convention

Some of the SHA-256 assembly functions push callee-save GPRs to the
stack *before* they set up the frame pointer (%rbp).  (They are leaf
functions, but they need to set up a frame pointer anyway because they
allocate a 16- or 32-byte-aligned buffer on the stack.)

As a result, during these functions, 8(%rbp) doesn't contain a return
address like it is supposed to.

This differs from the convention used by C code, and it interferes with
the frame pointer unwinder (CONFIG_UNWINDER_FRAME_POINTER=y).
Specifically, if a call trace is dumped in these functions, then all
entries are populated purely from the fallback scan of the entire stack:

    RIP: 0010:sha256_transform_rorx+0xd78/0x1120
    [...]
    Call Trace:
     <TASK>
     ? sha256_blocks_avx2+0x37/0x70
     ? __sha256_update+0x77/0x220
     ? sha256+0x9d/0x110
     [...]
     ? do_syscall_64+0x6f/0x3e0

With this fix to follow the normal %rbp convention, the call trace is
generated reliably:

    RIP: 0010:sha256_transform_rorx+0xdae/0x1120
    [...]
    Call Trace:
     <TASK>
     sha256_blocks_avx2+0x37/0x70
     __sha256_update+0x77/0x220
     sha256+0x9d/0x110
     [...]
     do_syscall_64+0x6f/0x3e0

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://patch.msgid.link/20261011134843.166585-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

0 files changed, 0 insertions, 0 deletions