On Tue, 23 Jan 2024 at 00:01, Sasha Levin <sashal@xxxxxxxxxx> wrote: > > This is a note to let you know that I've just added the patch titled > > arm64: scs: Work around full LTO issue with dynamic SCS > > to the 6.7-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > arm64-scs-work-around-full-lto-issue-with-dynamic-sc.patch > and it can be found in the queue-6.7 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@xxxxxxxxxxxxxxx> know about it. > Please drop this for now - we may end up reverting this. > > > commit 9d8d73251dc2720caa42aa1d3fc2f290232d9412 > Author: Ard Biesheuvel <ardb@xxxxxxxxxx> > Date: Wed Jan 10 14:26:20 2024 +0100 > > arm64: scs: Work around full LTO issue with dynamic SCS > > [ Upstream commit 8c5a19cb17a71e52303150335b459c7d2d28a155 ] > > 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 <ardb@xxxxxxxxxx> > Reviewed-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20240110132619.258809-2-ardb+git@xxxxxxxxxx > Signed-off-by: Will Deacon <will@xxxxxxxxxx> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > > 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
