netdev - Re: extended bpf_send_signal

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Message-ID: <YBgDOnhrYjByjdIb@hirez.programming.kicks-ass.net>
Date:   Mon, 1 Feb 2021 14:33:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, andrii@...nel.org,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...emloft.net>, kpsingh@...nel.org,
        John Fastabend <john.fastabend@...il.com>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: extended bpf_send_signal_thread with argument

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@...radead.org> 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.