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arm64: efi: Restore register x18 if it was corrupted 

If we detect a corrupted x18, restore the register before jumping back
to potentially SCS instrumented code. This is safe, because the wrapper
is called with preemption disabled and a separate shadow stack is used
for interrupt handling.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Sami Tolvanen 2020-04-27 09:00:13 -07:00 committed by Will Deacon
parent 6d37d81f44
commit e73f02c6eb
1 changed files with 10 additions and 1 deletions
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11
arch/arm64/kernel/efi-rt-wrapper.S
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@ -34,5 +34,14 @@ ENTRY(__efi_rt_asm_wrapper)
ldp x29, x30, [sp], #32
b.ne 0f
ret
0: b efi_handle_corrupted_x18 // tail call
0:
/*
* With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
* shadow stack pointer, which we need to restore before returning to
* potentially instrumented code. This is safe because the wrapper is
* called with preemption disabled and a separate shadow stack is used
* for interrupts.
*/
mov x18, x2
b efi_handle_corrupted_x18 // tail call
ENDPROC(__efi_rt_asm_wrapper)