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x86/ibt: Suppress spurious ENDBR

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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: 156ff4a544 ("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
This commit is contained in:
Peter Zijlstra
2023-08-02 12:55:46 +02:00
committed by Ingo Molnar
parent 5290e88ba2
commit 25e73b7e3f
2 changed files with 13 additions and 0 deletions
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5
include/linux/instruction_pointer.h
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@@ -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 */