6.1-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 25e73b7e3f72a25aa30cbb2eecb49036e0acf066 ]
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@amd.com Reviewed-by: Andrew Cooper andrew.cooper3@citrix.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20230802110323.016197440@infradead.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f484d656d34ee..3a0282a6a55df 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 cda1f706eaeb1..aa0b3ffea9353 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 */