linux-kernel - RE: [PATCH v4 19/23] kprobes: Remove kretprobe hash

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Date:   Fri, 28 Aug 2020 19:32:11 +0000
From:   "Eddy_Wu@...ndmicro.com" <Eddy_Wu@...ndmicro.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: RE: [PATCH v4 19/23] kprobes: Remove kretprobe hash


> -----Original Message-----
> From: Masami Hiramatsu <mhiramat@...nel.org>
>
> @@ -1311,24 +1257,23 @@ void kprobe_busy_end(void)
>  void kprobe_flush_task(struct task_struct *tk)
>  {
>         struct kretprobe_instance *ri;
> -       struct hlist_head *head;
> -       struct hlist_node *tmp;
> -       unsigned long hash, flags = 0;
> +       struct llist_node *node;
>
> +       /* Early boot, not yet initialized. */
>         if (unlikely(!kprobes_initialized))
> -               /* Early boot.  kretprobe_table_locks not yet initialized. */
>                 return;
>
>         kprobe_busy_begin();
>
> -       hash = hash_ptr(tk, KPROBE_HASH_BITS);
> -       head = &kretprobe_inst_table[hash];
> -       kretprobe_table_lock(hash, &flags);
> -       hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> -               if (ri->task == tk)
> -                       recycle_rp_inst(ri);
> +       node = current->kretprobe_instances.first;
> +       current->kretprobe_instances.first = NULL;

I think we are flushing tk instead of current here.
After fixing this to tk, the NULL pointer deference is gone!

> +
> +       while (node) {
> +               ri = container_of(node, struct kretprobe_instance, llist);
> +               node = node->next;
> +
> +               recycle_rp_inst(ri);
>         }
> -       kretprobe_table_unlock(hash, &flags);
>
>         kprobe_busy_end();
>  }

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