linux-kernel - Re: [PATCH v2] kprobes: Fix kill kprobe which has been marked as gone

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Date:   Mon, 31 Aug 2020 10:59:19 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     naveen.n.rao@...ux.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, Masami Hiramatsu <mhiramat@...nel.org>,
        songliubraving@...com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Chengming Zhou <zhouchengming@...edance.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] kprobes: Fix kill kprobe which has been marked as gone

Cc Andrew and Steven.

Any other comments or someone can add this to the queue for the
merge window? It's worth fixing it.

On Sat, Aug 22, 2020 at 11:01 AM Muchun Song <songmuchun@...edance.com> wrote:
>
> If a kprobe is marked as gone, we should not kill it again. Otherwise,
> we can disarm the kprobe more than once. In that case, the statistics
> of kprobe_ftrace_enabled can unbalance which can lead to that kprobe
> do not work.
>
> Fixes: e8386a0cb22f ("kprobes: support probing module __exit function")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Co-developed-by: Chengming Zhou <zhouchengming@...edance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
> changelogs in v2:
>  1. Add a WARN_ON_ONCE in the kill_kprobe() to catch incorrect use of it.
>  2. Update 'Fixes' tag in the commmit log.
>
>  kernel/kprobes.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d36e2b017588..9348b0c36ae0 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2143,6 +2143,9 @@ static void kill_kprobe(struct kprobe *p)
>
>         lockdep_assert_held(&kprobe_mutex);
>
> +       if (WARN_ON_ONCE(kprobe_gone(p)))
> +               return;
> +
>         p->flags |= KPROBE_FLAG_GONE;
>         if (kprobe_aggrprobe(p)) {
>                 /*
> @@ -2422,7 +2425,10 @@ static int kprobes_module_callback(struct notifier_block *nb,
>         mutex_lock(&kprobe_mutex);
>         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
>                 head = &kprobe_table[i];
> -               hlist_for_each_entry(p, head, hlist)
> +               hlist_for_each_entry(p, head, hlist) {
> +                       if (kprobe_gone(p))
> +                               continue;
> +
>                         if (within_module_init((unsigned long)p->addr, mod) ||
>                             (checkcore &&
>                              within_module_core((unsigned long)p->addr, mod))) {
> @@ -2439,6 +2445,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
>                                  */
>                                 kill_kprobe(p);
>                         }
> +               }
>         }
>         if (val == MODULE_STATE_GOING)
>                 remove_module_kprobe_blacklist(mod);
> --
> 2.11.0
>


--
Yours,
Muchun