x86/retbleed: Fix return thunk alignment

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commit 9a48d60467 upstream.

SYM_FUNC_START_LOCAL_NOALIGN() adds an endbr leading to this layout
(leaving only the last 2 bytes of the address):

  3bff <zen_untrain_ret>:
  3bff:       f3 0f 1e fa             endbr64
  3c03:       f6                      test   $0xcc,%bl

  3c04 <__x86_return_thunk>:
  3c04:       c3                      ret
  3c05:       cc                      int3
  3c06:       0f ae e8                lfence

However, "the RET at __x86_return_thunk must be on a 64 byte boundary,
for alignment within the BTB."

Use SYM_START instead.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Borislav Petkov (AMD) 2023-05-12 23:12:26 +02:00 • committed by Greg Kroah-Hartman

parent 2feac714c6

commit 000322b29c

1 changed files with 2 additions and 2 deletions

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arch/x86/lib/retpoline.S

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