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[1/4] arm64: assembler: Force error on misuse of .Lframe_local_offset

Message ID 20221129141803.1746898-2-ardb@kernel.org (mailing list archive)
State New, archived
Headers show
Series arm64: Add return address protection to asm code | expand

Commit Message

Ard Biesheuvel Nov. 29, 2022, 2:18 p.m. UTC 
The frame_push macro sets a local symbol .Lframe_local_offset to the
offset where the local variable area resides in the stack frame.
However, while we take care not to nest frame_push and frame_pop
sequences, .Lframe_local_offset retains its most recent value, allowing
it to be referenced erroneously from outside a frame_push/frame_pop
pair. So set it to an obviously wrong value that is guaranteed to
trigger a link error in frame_pop.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/assembler.h | 1 +
 1 file changed, 1 insertion(+)
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Patch

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 30eee6473cf0c0ea..3d1714a7eb6411ba 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -752,6 +752,7 @@  alternative_endif
 	.endif
 	ldp		x29, x30, [sp], #.Lframe_local_offset + .Lframe_extra
 	.set		.Lframe_regcount, -1
+	.set		.Lframe_local_offset, frame_local_offset_error
 	.endif
 	.endm