Re: [PATCH v1 8/8] tracing/bpf: Add might_fault check to syscall probes

[Steven Rostedt]

On Thu,  3 Oct 2024 11:16:38 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Tested-by: Andrii Nakryiko <andrii@xxxxxxxxxx> # BPF parts
> Cc: Michael Jeanson <mjeanson@xxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Yonghong Song <yhs@xxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: bpf@xxxxxxxxxxxxxxx
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> ---
>  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));	\
>  }