From 25e73b7e3f72a25aa30cbb2eecb49036e0acf066 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 2 Aug 2023 12:55:46 +0200 Subject: [PATCH] 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 Reviewed-by: Andrew Cooper Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230802110323.016197440@infradead.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 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 + #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 */ -- 2.7.4