Re: extended bpf_send_signal_thread with argument

[Peter Zijlstra]

On Mon, Feb 01, 2021 at 10:42:47AM +0100, Dmitry Vyukov wrote:
> On Mon, Feb 1, 2021 at 10:22 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Sun, Jan 31, 2021 at 12:14:02PM +0100, Dmitry Vyukov wrote:
> > > Hi,
> > >
> > > I would like to send a signal from a bpf program invoked from a
> > > perf_event. There is:
> >
> > You can't. Sending signals requires sighand lock, and you're not allowed
> > to take locks from perf_event context.
> 
> 
> Then we just found a vulnerability because there is
> bpf_send_signal_thread which can be attached to perf and it passes the
> verifier :)
> https://elixir.bootlin.com/linux/v5.11-rc5/source/kernel/trace/bpf_trace.c#L1145
> 
> It can defer sending the signal to the exit of irq context:
> https://elixir.bootlin.com/linux/v5.11-rc5/source/kernel/trace/bpf_trace.c#L1108
> Perhaps this is what makes it work?

Yes.