The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 25e73b7e3f72a25aa30cbb2eecb49036e0acf066
Gitweb: https://git.kernel.org/tip/25e73b7e3f72a25aa30cbb2eecb49036e0acf066
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 02 Aug 2023 12:55:46 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 12 Sep 2023 17:50:53 +02:00
x86/ibt: Suppress spurious ENDBR
It was reported that under certain circumstances GCC emits ENDBR
instructions for _THIS_IP_ usage. Specifically, when it appears at the
start of a basic block -- but not elsewhere.
Since _THIS_IP_ is never used for control flow, these ENDBR
instructions are completely superfluous. Override the _THIS_IP_
definition for x86_64 to avoid this.
Less ENDBR instructions is better.
Fixes: 156ff4a544ae ("x86/ibt: Base IBT bits")
Reported-by: David Kaplan <David.Kaplan@xxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230802110323.016197440@xxxxxxxxxxxxx
---
arch/x86/include/asm/linkage.h | 8 ++++++++
include/linux/instruction_pointer.h | 5 +++++
2 files changed, 13 insertions(+)
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 97a3de7..5ff49fd 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -8,6 +8,14 @@
#undef notrace
#define notrace __attribute__((no_instrument_function))
+#ifdef CONFIG_64BIT
+/*
+ * The generic version tends to create spurious ENDBR instructions under
+ * certain conditions.
+ */
+#define _THIS_IP_ ({ unsigned long __here; asm ("lea 0(%%rip), %0" : "=r" (__here)); __here; })
+#endif
+
#ifdef CONFIG_X86_32
#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
#endif /* CONFIG_X86_32 */
diff --git a/include/linux/instruction_pointer.h b/include/linux/instruction_pointer.h
index cda1f70..aa0b3ff 100644
--- a/include/linux/instruction_pointer.h
+++ b/include/linux/instruction_pointer.h
@@ -2,7 +2,12 @@
#ifndef _LINUX_INSTRUCTION_POINTER_H
#define _LINUX_INSTRUCTION_POINTER_H
+#include <asm/linkage.h>
+
#define _RET_IP_ (unsigned long)__builtin_return_address(0)
+
+#ifndef _THIS_IP_
#define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
+#endif
#endif /* _LINUX_INSTRUCTION_POINTER_H */
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