linux-kernel - [PATCH v2] kprobes: Rollback the aggrprobe post_handler on failed arm

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Message-Id: <20220619045028.50619-1-nashuiliang@gmail.com>
Date:   Sun, 19 Jun 2022 12:50:27 +0800
From:   Chuang W <nashuiliang@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Chuang W <nashuiliang@...il.com>, stable@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Jessica Yu <jeyu@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] kprobes: Rollback the aggrprobe post_handler on failed arm_kprobe()

In a scenario where livepatch and aggrprobe coexist on the same function
entry, and if this aggrprobe has a post_handler, arm_kprobe() always
fails as both livepatch and aggrprobe with post_handler will use
FTRACE_OPS_FL_IPMODIFY.
Since register_aggr_kprobe() doesn't roll back the post_handler on
failed arm_kprobe(), this aggrprobe will no longer be available even if
all kprobes on this aggrprobe don't have the post_handler.

Fix to roll back the aggrprobe post_handler for this case.
With this patch, if a kprobe that has the post_handler is removed from
this aggrprobe (since arm_kprobe() failed), it will be available again.

Fixes: 12310e343755 ("kprobes: Propagate error from arm_kprobe_ftrace()")
Signed-off-by: Chuang W <nashuiliang@...il.com>
Cc: <stable@...r.kernel.org>
---
v1 -> v2:
- Add commit details

 kernel/kprobes.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index f214f8c088ed..0610b02a3a05 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1300,6 +1300,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 {
 	int ret = 0;
 	struct kprobe *ap = orig_p;
+	kprobe_post_handler_t old_post_handler = NULL;
 
 	cpus_read_lock();
 
@@ -1351,6 +1352,9 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 
 	/* Copy the insn slot of 'p' to 'ap'. */
 	copy_kprobe(ap, p);
+
+	/* save the old post_handler */
+	old_post_handler = ap->post_handler;
 	ret = add_new_kprobe(ap, p);
 
 out:
@@ -1365,6 +1369,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 			ret = arm_kprobe(ap);
 			if (ret) {
 				ap->flags |= KPROBE_FLAG_DISABLED;
+				ap->post_handler = old_post_handler;
 				list_del_rcu(&p->list);
 				synchronize_rcu();
 			}
-- 
2.34.1