efi/libstub/x86: Use mandatory 16-byte stack alignment in mixed mode

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Reduce the stack frame of the EFI stub's mixed mode thunk routine by
8 bytes, by moving the GDT and return addresses to EBP and EBX, which
we need to preserve anyway, since their top halves will be cleared by
the call into 32-bit firmware code. Doing so results in the UEFI code
being entered with a 16 byte aligned stack, as mandated by the UEFI
spec, fixing the last occurrence in the 64-bit kernel where we violate
this requirement.

Also, move the saved GDT from a global variable to an unused part of the
stack frame, and touch up some other parts of the code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-3-ardb@kernel.org

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Ard Biesheuvel 2020-01-13 18:22:34 +01:00 • committed by Ingo Molnar

parent 796eb8d26a

commit ac3c76cc6d

1 changed files with 13 additions and 33 deletions

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arch/x86/boot/compressed/efi_thunk_64.S

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