[tip: x86/core] x86/ibt: Fix CC_HAS_IBT check for clang
From: tip-bot2 for Nathan Chancellor
Date: Sat Mar 12 2022 - 07:41:12 EST
The following commit has been merged into the x86/core branch of tip:
Commit-ID: f8afc9d88e65d189653f363eacc1f3131216ef7c
Gitweb: https://git.kernel.org/tip/f8afc9d88e65d189653f363eacc1f3131216ef7c
Author: Nathan Chancellor <nathan@xxxxxxxxxx>
AuthorDate: Fri, 11 Mar 2022 12:56:42 -07:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 12 Mar 2022 13:22:13 +01:00
x86/ibt: Fix CC_HAS_IBT check for clang
Commit 41c5ef31ad71 ("x86/ibt: Base IBT bits") added a check for a crash
in clang. However, this check does not work for two reasons.
The first reason is that '-pg' is missing from the check, which is
required for '-mfentry' to do anything.
The second reason is that cc-option only uses /dev/null as the input
file, which does not show a problem:
$ clang --version | head -1
Ubuntu clang version 12.0.1-8build1
$ clang -fcf-protection=branch -mfentry -pg -c -x c /dev/null -o /dev/null
$ echo $?
0
$ echo "void a(void) {}" | clang -fcf-protection=branch -mfentry -pg -c -x c - -o /dev/null
...
$ echo $?
139
Use this test instead so that the check works for older versions of
clang.
Fixes: 41c5ef31ad71 ("x86/ibt: Base IBT bits")
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220311195642.2033108-1-nathan@xxxxxxxxxx
---
arch/x86/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4ca7bfe..870e0d1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1867,7 +1867,7 @@ config CC_HAS_IBT
# Clang/LLVM >= 14
# fentry check to work around https://reviews.llvm.org/D111108
def_bool ((CC_IS_GCC && $(cc-option, -fcf-protection=branch -mindirect-branch-register)) || \
- (CC_IS_CLANG && $(cc-option, -fcf-protection=branch -mfentry))) && \
+ (CC_IS_CLANG && $(success,echo "void a(void) {}" | $(CC) -Werror $(CLANG_FLAGS) -fcf-protection=branch -mfentry -pg -x c - -c -o /dev/null))) && \
$(as-instr,endbr64)
config X86_KERNEL_IBT