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arm64: scs: Disable LTO for SCS patching code

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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: 3b619e22c4 ("arm64: implement dynamic shadow call stack for Clang")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20240123133052.1417449-6-ardb+git@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel 2024-01-23 14:30:55 +01:00 committed by Will Deacon
parent 2fa28abd10
commit d104a6fef3
1 changed files with 6 additions and 0 deletions
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6
arch/arm64/kernel/Makefile
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@ -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