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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

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@linutronix.de>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Michael Jeanson <mjeanson@efficios.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Yonghong Song <yhs@fb.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: bpf@vger.kernel.org
> Cc: Joel Fernandes <joel@joelfernandes.org>
> Cc: Jordan Rife <jrife@google.com>
> ---
>   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.

Thanks,

Mathieu

> +		} else {						\
>   			preempt_disable_notrace();			\
> +		}							\
>   									\
>   		__DO_TRACE_CALL(name, TP_ARGS(args));			\
>   									\

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com