From: Ard Biesheuvel Date: Tue, 23 Jan 2024 13:30:55 +0000 (+0100) Subject: arm64: scs: Disable LTO for SCS patching code X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=d104a6fef3fec137d8d44961224ab76edbd6cbc7;p=users%2Fjedix%2Flinux-maple.git arm64: scs: Disable LTO for SCS patching code 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 disabling LTO for the compilation unit, which appears to convince the linker that it should still use PAC in the rest of the kernel.. Fixes: 3b619e22c460 ("arm64: implement dynamic shadow call stack for Clang") Signed-off-by: Ard Biesheuvel Reviewed-by: Kees Cook Reviewed-by: Sami Tolvanen Tested-by: Sami Tolvanen Link: https://lore.kernel.org/r/20240123133052.1417449-6-ardb+git@google.com Signed-off-by: Will Deacon --- diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index d95b3d6b471a7..467cb71172730 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 + +# 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 disable LTO as well for the compilation unit. CFLAGS_patch-scs.o += -mbranch-protection=none +CFLAGS_REMOVE_patch-scs.o += $(CC_FLAGS_LTO) # Force dependency (vdso*-wrap.S includes vdso.so through incbin) $(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so