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arm64: Revert "scs: Work around full LTO issue with dynamic SCS"

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This reverts commit 8c5a19cb17 ("arm64: scs: Work around full LTO
issue with dynamic SCS"), which did not quite fix the issue as intended.
Apparently, -fno-unwind-tables is ignored for the final full LTO link
when it is set on any of the objects, resulting in an early boot crash
due to the SCS patching code patching itself, and attempting to pop the
return address from the shadow stack while the associated push was still
a PACIASP instruction when it executed.

Reported-by: Sami Tolvanen <samitolvanen@google.com>
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/20240123133052.1417449-5-ardb+git@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel 2024-01-23 14:30:54 +01:00 committed by Will Deacon
parent 41bccc98fb
commit 2fa28abd10
1 changed files with 1 additions and 7 deletions
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8
arch/arm64/kernel/Makefile
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@ -73,13 +73,7 @@ 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 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
CFLAGS_patch-scs.o += -mbranch-protection=none
# Force dependency (vdso*-wrap.S includes vdso.so through incbin)
$(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so