Re: [PATCH 0/2] kprobes: Fix kretprobe incorrect stacking order problem
From: Andrea Righi
Date: Mon Jan 07 2019 - 16:34:45 EST
On Mon, Jan 07, 2019 at 04:28:33PM -0500, Steven Rostedt wrote:
> On Mon, 7 Jan 2019 22:19:04 +0100
> Andrea Righi <righi.andrea@xxxxxxxxx> wrote:
> > > > If we put a kretprobe to raw_spin_lock_irqsave() it looks like
> > > > kretprobe is going to call kretprobe...
> > >
> > > Right, but we should be able to add some recursion protection to stop
> > > that. I have similar protection in the ftrace code.
> > If we assume that __raw_spin_lock/unlock*() are always inlined a
> I wouldn't assume that.
> > possible way to prevent this recursion could be to use directly those
> > functions to do locking from the kretprobe trampoline.
> > But I'm not sure if that's a safe assumption... if not I'll see if I can
> > find a better solution.
> All you need to do is have a per_cpu variable, where you just do:
> if (this_cpu_read(kprobe_recursion))
> goto out;
> And then just ignore any kprobes that trigger while you are processing
> the current kprobe.
> Something like that. If you want (or if it already happens) replace
> preempt_disable() with local_irq_save().
Oh.. definitely much better. I'll work on that and send a new patch.
Thanks for the suggestion!