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    SubjectRe: [PATCH v4 19/23] kprobes: Remove kretprobe hash
    On Fri, 28 Aug 2020 22:29:12 +0200
    Peter Zijlstra <peterz@infradead.org> wrote:

    > On Fri, Aug 28, 2020 at 07:32:11PM +0000, Eddy_Wu@trendmicro.com wrote:
    > >
    > > > -----Original Message-----
    > > > From: Masami Hiramatsu <mhiramat@kernel.org>
    > > >
    > > > @@ -1311,24 +1257,23 @@ void kprobe_busy_end(void)
    > > > void kprobe_flush_task(struct task_struct *tk)
    > > > {
    > > > struct kretprobe_instance *ri;
    > > > + struct llist_node *node;
    > > >
    > > > + /* Early boot, not yet initialized. */
    > > > if (unlikely(!kprobes_initialized))
    > > > return;
    > > >
    > > > kprobe_busy_begin();
    > > >
    > > > + 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!
    >

    Cool!!

    > Ah, very good! I can indeed confirm that that cures things.

    OK, I'll merge this too.

    Thank you,

    >
    > ---
    > Index: linux-2.6/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.orig/kernel/kprobes.c
    > +++ linux-2.6/kernel/kprobes.c
    > @@ -1275,9 +1275,7 @@ void kprobe_flush_task(struct task_struc
    >
    > kprobe_busy_begin();
    >
    > - node = current->kretprobe_instances.first;
    > - current->kretprobe_instances.first = NULL;
    > -
    > + node == __llist_del_all(&tk->kretprobe_instances);
    > while (node) {
    > ri = container_of(node, struct kretprobe_instance, llist);
    > node = node->next;
    > @@ -1871,6 +1869,7 @@ unsigned long __kretprobe_trampoline_han
    > struct llist_node *first, *node;
    > struct kretprobe *rp;
    >
    > + /* Find all nodes for this frame. */
    > first = node = current->kretprobe_instances.first;
    > while (node) {
    > ri = container_of(node, struct kretprobe_instance, llist);
    > @@ -1900,7 +1899,7 @@ unsigned long __kretprobe_trampoline_han
    > while (first) {
    > ri = container_of(first, struct kretprobe_instance, llist);
    > rp = get_kretprobe(ri);
    > - node = first->next;
    > + first = first->next;
    >
    > if (rp && rp->handler) {
    > __this_cpu_write(current_kprobe, &rp->kp);
    > @@ -1910,8 +1909,6 @@ unsigned long __kretprobe_trampoline_han
    > }
    >
    > recycle_rp_inst(ri);
    > -
    > - first = node;
    > }
    >
    > return (unsigned long)correct_ret_addr;
    > Index: linux-2.6/include/linux/llist.h
    > ===================================================================
    > --- linux-2.6.orig/include/linux/llist.h
    > +++ linux-2.6/include/linux/llist.h
    > @@ -237,6 +237,14 @@ static inline struct llist_node *llist_d
    > return xchg(&head->first, NULL);
    > }
    >
    > +static inline struct llist_node *__llist_del_all(struct llist_head *head)
    > +{
    > + struct llist_node *first = head->first;
    > +
    > + head->first = NULL;
    > + return first;
    > +}
    > +
    > extern struct llist_node *llist_del_first(struct llist_head *head);
    >
    > struct llist_node *llist_reverse_order(struct llist_node *head);
    >


    --
    Masami Hiramatsu <mhiramat@kernel.org>

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