This is a note to let you know that I've just added the patch titled
arm64: Restrict ARM64_BTI_KERNEL to clang 12.0.0 and newer
to the 5.10-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-restrict-arm64_bti_kernel-to-clang-12.0.0-and-.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 35c4cf7e6d21f5ed5b6c2030f6e51483dacc49a7
Author: Nathan Chancellor <nathan@xxxxxxxxxx>
Date: Mon Jul 12 14:46:37 2021 -0700
arm64: Restrict ARM64_BTI_KERNEL to clang 12.0.0 and newer
[ Upstream commit 8cdd23c23c3d481a43b4aa03dcb5738812831115 ]
Commit 97fed779f2a6 ("arm64: bti: Provide Kconfig for kernel mode BTI")
disabled CONFIG_ARM64_BTI_KERNEL when CONFIG_GCOV_KERNEL was enabled and
compiling with clang because of warnings that were seen with
allmodconfig because LLVM was not emitting PAC/BTI instructions for
compiler generated functions:
| warning: some functions compiled with BTI and some compiled without BTI
| warning: not setting BTI in feature flags
This dependency was fine for avoiding the warnings with allmodconfig
until commit 51c2ee6d121c ("Kconfig: Introduce ARCH_WANTS_NO_INSTR and
CC_HAS_NO_PROFILE_FN_ATTR"), which prevents CONFIG_GCOV_KERNEL from
being enabled with clang 12.0.0 or older because those versions do not
support the no_profile_instrument_function attribute.
As a result, CONFIG_ARM64_BTI_KERNEL gets enabled with allmodconfig and
there are more warnings like the ones above due to CONFIG_KASAN, which
suffers from the same problem as CONFIG_GCOV_KERNEL. This was most
likely not noticed at the time because allmodconfig +
CONFIG_GCOV_KERNEL=n was not tested. defconfig + CONFIG_KASAN=y is
enough to reproduce the same warnings as above.
The root cause of the warnings was resolved in LLVM during the 12.0.0
release so rather than play whack-a-mole with the dependencies, just
update CONFIG_ARM64_BTI_KERNEL to require clang 12.0.0, which will have
all of the issues ironed out.
Link: https://github.com/ClangBuiltLinux/linux/issues/1428
Link: https://github.com/ClangBuiltLinux/continuous-integration2/runs/3010034706?check_suite_focus=true
Link: https://github.com/ClangBuiltLinux/continuous-integration2/runs/3010035725?check_suite_focus=true
Link: https://github.com/llvm/llvm-project/commit/a88c722e687e6780dcd6a58718350dc76fcc4cc9
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210712214636.3134425-1-nathan@xxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Stable-dep-of: c0a454b9044f ("arm64/bti: Disable in kernel BTI when cross section thunks are broken")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1116a8d092c0..662311a513f0 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1654,7 +1654,8 @@ config ARM64_BTI_KERNEL
depends on CC_HAS_BRANCH_PROT_PAC_RET_BTI
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94697
depends on !CC_IS_GCC || GCC_VERSION >= 100100
- depends on !(CC_IS_CLANG && GCOV_KERNEL)
+ # https://github.com/llvm/llvm-project/commit/a88c722e687e6780dcd6a58718350dc76fcc4cc9
+ depends on !CC_IS_CLANG || CLANG_VERSION >= 120000
depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
help
Build the kernel with Branch Target Identification annotations
