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[1/2] arm64: Revert "scs: Work around full LTO issue with dynamic SCS"

Message ID 20240123133052.1417449-5-ardb+git@google.com (mailing list archive)
State New, archived
Headers show
Series arm64: Fix for dynamic SCS under full LTO take #2 | expand

Commit Message

Ard Biesheuvel Jan. 23, 2024, 1:30 p.m. UTC 
From: Ard Biesheuvel <ardb@kernel.org>

This reverts commit 8c5a19cb17a71e ("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>
---
 arch/arm64/kernel/Makefile | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index e5d03a7039b4..d95b3d6b471a 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -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