From 8c5a19cb17a71e52303150335b459c7d2d28a155 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 10 Jan 2024 14:26:20 +0100 Subject: arm64: scs: Work around full LTO issue with dynamic SCS Full LTO takes the '-mbranch-protection=none' passed to the compiler when generating the dynamic shadow call stack patching code as a hint to stop emitting PAC instructions altogether. (Thin LTO appears unaffected by this) Work around this by stripping unwind tables from the object in question, which should be sufficient to prevent the patching code from attempting to patch itself. Fixes: 3b619e22c460 ("arm64: implement dynamic shadow call stack for Clang") Signed-off-by: Ard Biesheuvel Reviewed-by: Sami Tolvanen Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20240110132619.258809-2-ardb+git@google.com Signed-off-by: Will Deacon --- arch/arm64/kernel/Makefile | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'arch/arm64') diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index d95b3d6b471a..e5d03a7039b4 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -73,7 +73,13 @@ obj-$(CONFIG_ARM64_MTE) += mte.o obj-y += vdso-wrap.o obj-$(CONFIG_COMPAT_VDSO) += vdso32-wrap.o obj-$(CONFIG_UNWIND_PATCH_PAC_INTO_SCS) += patch-scs.o -CFLAGS_patch-scs.o += -mbranch-protection=none + +# We need to prevent the SCS patching code from patching itself. Using +# -mbranch-protection=none here to avoid the patchable PAC opcodes from being +# generated triggers an issue with full LTO on Clang, which stops emitting PAC +# instructions altogether. So instead, omit the unwind tables used by the +# patching code, so it will not be able to locate its own PAC instructions. +CFLAGS_patch-scs.o += -fno-asynchronous-unwind-tables -fno-unwind-tables # Force dependency (vdso*-wrap.S includes vdso.so through incbin) $(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so -- cgit