3 messages, 2 authors, 2021-02-01 · open the first message on its own page
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-02-01 09:23:55
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.
From: Dmitry Vyukov <dvyukov@google.com>
Date: 2021-02-01 09:43:44
On Mon, Feb 1, 2021 at 10:22 AM Peter Zijlstra [off-list ref] wrote:
On Sun, Jan 31, 2021 at 12:14:02PM +0100, Dmitry Vyukov wrote:quoted
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?
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-02-01 13:35:14
On Mon, Feb 01, 2021 at 10:42:47AM +0100, Dmitry Vyukov wrote:
On Mon, Feb 1, 2021 at 10:22 AM Peter Zijlstra [off-list ref] wrote:quoted
On Sun, Jan 31, 2021 at 12:14:02PM +0100, Dmitry Vyukov wrote:quoted
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.