The following commit has been merged into the x86/core branch of tip: Commit-ID: 262448f3d18959d175b10e28a3b65f41d1d7313f Gitweb: https://git.kernel.org/tip/262448f3d18959d175b10e28a3b65f41d1d7313f Author: Nathan Chancellor <nathan@xxxxxxxxxx> AuthorDate: Fri, 18 Mar 2022 16:07:46 -07:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Tue, 22 Mar 2022 21:12:13 +01:00 x86/Kconfig: Only enable CONFIG_CC_HAS_IBT for clang >= 14.0.0 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. Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220318230747.3900772-2-nathan@xxxxxxxxxx --- arch/x86/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 0f0672d..921e4eb 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
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