linux-kernel - Re: [PATCH v1 8/8] tracing/bpf: Add might

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Message-ID: <20241003183830.16155ec3@gandalf.local.home>
Date: Thu, 3 Oct 2024 18:38:30 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
 Peter Zijlstra <peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>,
 Yonghong Song <yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>, Ingo
 Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark
 Rutland <mark.rutland@....com>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>, bpf@...r.kernel.org, Joel
 Fernandes <joel@...lfernandes.org>, linux-trace-kernel@...r.kernel.org,
 Andrii Nakryiko <andrii@...nel.org>, Michael Jeanson
 <mjeanson@...icios.com>
Subject: Re: [PATCH v1 8/8] tracing/bpf: Add might_fault check to syscall
 probes

On Thu,  3 Oct 2024 11:16:38 -0400
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> Add a might_fault() check to validate that the bpf sys_enter/sys_exit
> probe callbacks are indeed called from a context where page faults can
> be handled.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> Tested-by: Andrii Nakryiko <andrii@...nel.org> # BPF parts
> Cc: Michael Jeanson <mjeanson@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: bpf@...r.kernel.org
> Cc: Joel Fernandes <joel@...lfernandes.org>
> ---
>  include/trace/bpf_probe.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index 211b98d45fc6..099df5c3e38a 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -57,6 +57,7 @@ __bpf_trace_##call(void *__data, proto)					\
>  static notrace void							\
>  __bpf_trace_##call(void *__data, proto)					\
>  {									\
> +	might_fault();							\

And I think this gets called at places that do not allow faults.

-- Steve

>  	guard(preempt_notrace)();					\
>  	CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(__data, CAST_TO_U64(args));	\
>  }