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 16:20, Andrii Nakryiko wrote:
> On Mon, Oct 28, 2024 at 12:59 PM Mathieu Desnoyers
> <mathieu.desnoyers@efficios.com> 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@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.
> 
> please drop the RFC tag while at it

I'm still awaiting for Jordan (or someone else) to come back with
testing results before I feel confident dropping the RFC tag.

Thanks,

Mathieu

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

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