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    Subject[PATCH 5.0 089/115] x86/kprobes: Avoid kretprobe recursion bug
    Date
    From: Masami Hiramatsu <mhiramat@kernel.org>

    commit b191fa96ea6dc00d331dcc28c1f7db5e075693a0 upstream.

    Avoid kretprobe recursion loop bg by setting a dummy
    kprobes to current_kprobe per-CPU variable.

    This bug has been introduced with the asm-coded trampoline
    code, since previously it used another kprobe for hooking
    the function return placeholder (which only has a nop) and
    trampoline handler was called from that kprobe.

    This revives the old lost kprobe again.

    With this fix, we don't see deadlock anymore.

    And you can see that all inner-called kretprobe are skipped.

    event_1 235 0
    event_2 19375 19612

    The 1st column is recorded count and the 2nd is missed count.
    Above shows (event_1 rec) + (event_2 rec) ~= (event_2 missed)
    (some difference are here because the counter is racy)

    Reported-by: Andrea Righi <righi.andrea@gmail.com>
    Tested-by: Andrea Righi <righi.andrea@gmail.com>
    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: stable@vger.kernel.org
    Fixes: c9becf58d935 ("[PATCH] kretprobe: kretprobe-booster")
    Link: http://lkml.kernel.org/r/155094064889.6137.972160690963039.stgit@devbox
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/kprobes/core.c | 22 ++++++++++++++++++++--
    1 file changed, 20 insertions(+), 2 deletions(-)

    --- a/arch/x86/kernel/kprobes/core.c
    +++ b/arch/x86/kernel/kprobes/core.c
    @@ -749,11 +749,16 @@ asm(
    NOKPROBE_SYMBOL(kretprobe_trampoline);
    STACK_FRAME_NON_STANDARD(kretprobe_trampoline);

    +static struct kprobe kretprobe_kprobe = {
    + .addr = (void *)kretprobe_trampoline,
    +};
    +
    /*
    * Called from kretprobe_trampoline
    */
    static __used void *trampoline_handler(struct pt_regs *regs)
    {
    + struct kprobe_ctlblk *kcb;
    struct kretprobe_instance *ri = NULL;
    struct hlist_head *head, empty_rp;
    struct hlist_node *tmp;
    @@ -763,6 +768,17 @@ static __used void *trampoline_handler(s
    void *frame_pointer;
    bool skipped = false;

    + preempt_disable();
    +
    + /*
    + * Set a dummy kprobe for avoiding kretprobe recursion.
    + * Since kretprobe never run in kprobe handler, kprobe must not
    + * be running at this point.
    + */
    + kcb = get_kprobe_ctlblk();
    + __this_cpu_write(current_kprobe, &kretprobe_kprobe);
    + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
    +
    INIT_HLIST_HEAD(&empty_rp);
    kretprobe_hash_lock(current, &head, &flags);
    /* fixup registers */
    @@ -838,10 +854,9 @@ static __used void *trampoline_handler(s
    orig_ret_address = (unsigned long)ri->ret_addr;
    if (ri->rp && ri->rp->handler) {
    __this_cpu_write(current_kprobe, &ri->rp->kp);
    - get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
    ri->ret_addr = correct_ret_addr;
    ri->rp->handler(ri, regs);
    - __this_cpu_write(current_kprobe, NULL);
    + __this_cpu_write(current_kprobe, &kretprobe_kprobe);
    }

    recycle_rp_inst(ri, &empty_rp);
    @@ -857,6 +872,9 @@ static __used void *trampoline_handler(s

    kretprobe_hash_unlock(current, &flags);

    + __this_cpu_write(current_kprobe, NULL);
    + preempt_enable();
    +
    hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
    hlist_del(&ri->hlist);
    kfree(ri);

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