linux-kernel - [PATCH] kprobes/x86: Skip the assignment to ip when there is no post

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Message-Id: <20200520145007.35479-1-songmuchun@bytedance.com>
Date:   Wed, 20 May 2020 22:50:07 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mingo@...nel.org, bp@...en8.de, x86@...nel.org, hpa@...or.com
Cc:     allison@...utok.net, gregkh@...uxfoundation.org,
        rfontana@...hat.com, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH] kprobes/x86: Skip the assignment to ip when there is no post_handler

When there is no post_handler, the assignment to ip of regs is
meaningless. So just skip it.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 arch/x86/kernel/kprobes/ftrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 681a4b36e9bbe..f1edc0dc860a2 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -39,8 +39,8 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 			 * Emulate singlestep (and also recover regs->ip)
 			 * as if there is a 5byte nop
 			 */
-			regs->ip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;
 			if (unlikely(p->post_handler)) {
+				regs->ip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;
 				kcb->kprobe_status = KPROBE_HIT_SSDONE;
 				p->post_handler(p, regs, 0);
 			}
-- 
2.11.0