Commit 25e73b7e authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: 156ff4a5 ("x86/ibt: Base IBT bits")
Reported-by: default avatarDavid Kaplan <David.Kaplan@amd.com>
Reviewed-by: default avatarAndrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230802110323.016197440@infradead.org
parent 5290e88b

arch/x86/include/asm/linkage.h

+8 −0
Original line number Diff line number Diff line
@@ -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 */

include/linux/instruction_pointer.h

+5 −0
Original line number Diff line number Diff line
@@ -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 */