Commit 1105ab42 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
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x86/sev: Disable jump tables in SEV startup code 



When retpolines and IBT are both disabled, the compiler is free to use
jump tables to optimize switch instructions. However, these are emitted
by Clang as absolute references into .rodata:

        jmp    *-0x7dfffe90(,%r9,8)
                        R_X86_64_32S    .rodata+0x170

Given that this code will execute before that address in .rodata has even
been mapped, it is guaranteed to crash a SEV-SNP guest in a way that is
difficult to diagnose.

So disable jump tables when building this code. It would be better if we
could attach this annotation to the __head macro but this appears to be
impossible.

Reported-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Tested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250127114334.1045857-6-ardb+git@google.com
parent 9c5968db

arch/x86/coco/sev/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -2,6 +2,10 @@ 


obj-y += core.o



# jump tables are emitted using absolute references in non-PIC code

# so they cannot be used in the early SEV startup code

CFLAGS_core.o += -fno-jump-tables



ifdef CONFIG_FUNCTION_TRACER

CFLAGS_REMOVE_core.o = -pg

endif