Re: [RFC PATCH v4 4/4] tracing: Add might_fault() check in __DO_TRACE() for syscall

[Andrii Nakryiko]

On Mon, Oct 28, 2024 at 12:59 PM Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>
> On 2024-10-28 15:09, Mathieu Desnoyers wrote:
> > Catch incorrect use of syscall tracepoints even if no probes are
> > registered by adding a might_fault() check in __DO_TRACE() when
> > syscall=1.
> >
> > Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > 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>
> > Cc: Jordan Rife <jrife@xxxxxxxxxx>
> > ---
> >   include/linux/tracepoint.h | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index 259f0ab4ece6..7bed499b7055 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -226,10 +226,12 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> >               if (!(cond))                                            \
> >                       return;                                         \
> >                                                                       \
> > -             if (syscall)                                            \
> > +             if (syscall) {                                          \
> >                       rcu_read_lock_trace();                          \
> > -             else                                                    \
> > +                     might_fault();                                  \
>
> Actually, __DO_TRACE() is not the best place to put this, because it's
> only executed when the tracepoint is enabled.
>
> I'll move this to __DECLARE_TRACE_SYSCALL()
>
> #define __DECLARE_TRACE_SYSCALL(name, proto, args, cond, data_proto)    \
>          __DECLARE_TRACE_COMMON(name, PARAMS(proto), PARAMS(args), cond, PARAMS(data_proto)) \
>          static inline void trace_##name(proto)                          \
>          {                                                               \
>                  might_fault();                                          \
>                  if (static_branch_unlikely(&__tracepoint_##name.key))   \
>                          __DO_TRACE(name,                                \
>                                  TP_ARGS(args),                          \
>                                  TP_CONDITION(cond), 1);                 \
> [...]
>
> instead in v5.

please drop the RFC tag while at it

>
> Thanks,
>
> Mathieu
>
> > +             } else {                                                \
> >                       preempt_disable_notrace();                      \
> > +             }                                                       \
> >                                                                       \
> >               __DO_TRACE_CALL(name, TP_ARGS(args));                   \
> >                                                                       \
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>