Messages in this thread Patch in this message | | | From | Nathan Chancellor <> | Subject | [PATCH 1/2] x86/Kconfig: Only enable CONFIG_CC_HAS_IBT for clang >= 14.0.0 | Date | Fri, 18 Mar 2022 16:07:46 -0700 |
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Commit 156ff4a544ae ("x86/ibt: Base IBT bits") added a check for a crash with 'clang -fcf-protection=branch -mfentry -pg', which intended to exclude Clang versions older than 14.0.0 from selecting CONFIG_X86_KERNEL_IBT.
clang-11 does not have the issue that the check is testing for, so CONFIG_X86_KERNEL_IBT is selectable. Unfortunately, there is a different crash in clang-11 that was fixed in clang-12. To make matters worse, that crash does not appear to be entirely deterministic, as the same input to the compiler will sometimes crash and other times not, which makes dynamically checking for the crash like the '-pg' one unreliable.
To make everything work properly for all common versions of clang, use a hard version check of 14.0.0, as that will be the first release upstream that has both bugs properly fixed.
Link: https://github.com/llvm/llvm-project/commit/e0b89df2e0f0130881bf6c39bf31d7f6aac00e0f Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- arch/x86/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 0f0672d2c816..921e4ebda564 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1865,9 +1865,10 @@ config CC_HAS_IBT # GCC >= 9 and binutils >= 2.29 # Retpoline check to work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93654 # Clang/LLVM >= 14 - # fentry check to work around https://reviews.llvm.org/D111108 + # https://github.com/llvm/llvm-project/commit/e0b89df2e0f0130881bf6c39bf31d7f6aac00e0f + # https://github.com/llvm/llvm-project/commit/dfcf69770bc522b9e411c66454934a37c1f35332 def_bool ((CC_IS_GCC && $(cc-option, -fcf-protection=branch -mindirect-branch-register)) || \ - (CC_IS_CLANG && $(success,echo "void a(void) {}" | $(CC) -Werror $(CLANG_FLAGS) -fcf-protection=branch -mfentry -pg -x c - -c -o /dev/null))) && \ + (CC_IS_CLANG && CLANG_VERSION >= 140000)) && \ $(as-instr,endbr64) config X86_KERNEL_IBT -- 2.35.1
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