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Patch "kprobes/x86: Disable preemption in ftrace-based jprobes" has been added to the 4.4-stable tree

PATCH [email protected] 1 participant 1 message Dec 6, 2017

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This is a note to let you know that I've just added the patch titled

kprobes/x86: Disable preemption in ftrace-based jprobes

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Wed Dec 6 16:43:17 CET 2017

From: Masami Hiramatsu <[email protected]>
Date: Tue, 19 Sep 2017 19:01:40 +0900
Subject: kprobes/x86: Disable preemption in ftrace-based jprobes

From: Masami Hiramatsu <[email protected]>

[ Upstream commit 5bb4fc2d8641219732eb2bb654206775a4219aca ]

Disable preemption in ftrace-based jprobe handlers as described in Documentation/kprobes.txt:

"Probe handlers are run with preemption disabled."

This will fix jprobes behavior when CONFIG_PREEMPT=y.

Signed-off-by Masami Hiramatsu <[email protected]>
Cc Alexei Starovoitov <[email protected]>
Cc Alexei Starovoitov <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Paul E . McKenney <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Steven Rostedt <[email protected]>
Cc Thomas Gleixner <[email protected]>
Link http://lkml.kernel.org/r/150581530024.32348.9863783558598926771.stgit@devbox open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Sasha Levin <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/kernel/kprobes/ftrace.c |   23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)
arch/x86/kernel/kprobes/ftrace.c +14 -9
@@ -26,7 +26,7 @@
 #include "common.h"
 
 static nokprobe_inline
-int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
+void __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
 		      struct kprobe_ctlblk *kcb, unsigned long orig_ip)
 {
 	/*

@@ -41,20 +41,21 @@ int __skip_singlestep(struct kprobe *p,
 	__this_cpu_write(current_kprobe, NULL);
 	if (orig_ip)
 		regs->ip = orig_ip;
-	return 1;
 }
 
 int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
 		    struct kprobe_ctlblk *kcb)
 {
-	if (kprobe_ftrace(p))
-		return __skip_singlestep(p, regs, kcb, 0);
-	else
-		return 0;
+	if (kprobe_ftrace(p)) {
+		__skip_singlestep(p, regs, kcb, 0);
+		preempt_enable_no_resched();
+		return 1;
+	}
+	return 0;
 }
 NOKPROBE_SYMBOL(skip_singlestep);
 
-/* Ftrace callback handler for kprobes */
+/* Ftrace callback handler for kprobes -- called under preepmt disabed */
 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 			   struct ftrace_ops *ops, struct pt_regs *regs)
 {

@@ -77,13 +78,17 @@ void kprobe_ftrace_handler(unsigned long
 		/* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
 		regs->ip = ip + sizeof(kprobe_opcode_t);
 
+		/* To emulate trap based kprobes, preempt_disable here */
+		preempt_disable();
 		__this_cpu_write(current_kprobe, p);
 		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
-		if (!p->pre_handler || !p->pre_handler(p, regs))
+		if (!p->pre_handler || !p->pre_handler(p, regs)) {
 			__skip_singlestep(p, regs, kcb, orig_ip);
+			preempt_enable_no_resched();
+		}
 		/*
 		 * If pre_handler returns !0, it sets regs->ip and
-		 * resets current kprobe.
+		 * resets current kprobe, and keep preempt count +1.
 		 */
 	}
 end:

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch