From 1105ab42a84bc11c62597005f78ccad2434fbd66 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Mon, 27 Jan 2025 12:43:37 +0100 Subject: [PATCH] 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: Linus Torvalds Tested-by: Linus Torvalds Signed-off-by: Ard Biesheuvel Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20250127114334.1045857-6-ardb+git@google.com --- arch/x86/coco/sev/Makefile | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/coco/sev/Makefile b/arch/x86/coco/sev/Makefile index 08de375593074..dcb06dc8b5aea 100644 --- a/arch/x86/coco/sev/Makefile +++ b/arch/x86/coco/sev/Makefile @@ -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 -- 2.49.0