2022-06-19 06:19:17

by Chuang Wang

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 <[email protected]>
Cc: <[email protected]>
---
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

2022-06-21 15:54:40

by Masami Hiramatsu

Subject: Re: [PATCH v2] kprobes: Rollback the aggrprobe post_handler on failed arm_kprobe()

On Sun, 19 Jun 2022 12:50:27 +0800
Chuang W <[email protected]> wrote:

> 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.
>

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <[email protected]>

Thank you!

> Fixes: 12310e343755 ("kprobes: Propagate error from arm_kprobe_ftrace()")
> Signed-off-by: Chuang W <[email protected]>
> Cc: <[email protected]>
> ---
> 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
>


--
Masami Hiramatsu (Google) <[email protected]>