On Tue, 5 Nov 2024 at 17:31, Steven Rostedt <[email protected]> wrote: > > On Tue, 5 Nov 2024 14:34:05 +0100 > Marco Elver <[email protected]> wrote: > > > prctl() is a complex syscall which multiplexes its functionality based > > on a large set of PR_* options. Currently we count 64 such options. The > > return value of unknown options is -EINVAL, and doesn't distinguish from > > known options that were passed invalid args that also return -EINVAL. > > > > To understand if programs are attempting to use prctl() options not yet > > available on the running kernel, provide the task_prctl_unknown > > tracepoint. > > > > Note, this tracepoint is in an unlikely cold path, and would therefore > > be suitable for continuous monitoring (e.g. via perf_event_open). > > > > While the above is likely the simplest usecase, additionally this > > tracepoint can help unlock some testing scenarios (where probing > > sys_enter or sys_exit causes undesirable performance overheads): > > > > a. unprivileged triggering of a test module: test modules may register a > > probe to be called back on task_prctl_unknown, and pick a very large > > unknown prctl() option upon which they perform a test function for an > > unprivileged user; > > > > b. unprivileged triggering of an eBPF program function: similar > > as idea (a). > > > > Example trace_pipe output: > > > > <...>-366 [004] ..... 146.439400: task_prctl_unknown: pid=366 > > comm=a.out option=1234 arg2=101 arg3=102 arg4=103 arg5=104 > > ^^^ ^^^ > > > > > Signed-off-by: Marco Elver <[email protected]> > > --- > > include/trace/events/task.h | 43 +++++++++++++++++++++++++++++++++++++ > > kernel/sys.c | 3 +++ > > 2 files changed, 46 insertions(+) > > > > diff --git a/include/trace/events/task.h b/include/trace/events/task.h > > index 47b527464d1a..ab711e581094 100644 > > --- a/include/trace/events/task.h > > +++ b/include/trace/events/task.h > > @@ -56,6 +56,49 @@ TRACE_EVENT(task_rename, > > __entry->newcomm, __entry->oom_score_adj) > > ); > > > > +/** > > + * task_prctl_unknown - called on unknown prctl() option > > + * @task: pointer to the current task > > + * @option: option passed > > + * @arg2: arg2 passed > > + * @arg3: arg3 passed > > + * @arg4: arg4 passed > > + * @arg5: arg5 passed > > + * > > + * Called on an unknown prctl() option. > > + */ > > +TRACE_EVENT(task_prctl_unknown, > > + > > + TP_PROTO(struct task_struct *task, int option, unsigned long arg2, > > unsigned long arg3, > > + unsigned long arg4, unsigned long arg5), > > + > > + TP_ARGS(task, option, arg2, arg3, arg4, arg5), > > + > > + TP_STRUCT__entry( > > + __field( pid_t, pid ) > > Why record the pid that is already recorded by the event header?
To keep in style with the other "task" tracepoints above. I can certainly do without - it does seem unnecessary. To cleanup, do we want to remove "pid=" from the other tracepoints in this file as well (in another patch). Or does this potentially break existing users? > > + __string( comm, task->comm ) > > I'm also surprised that the comm didn't show in the trace_pipe. Any config options or tweaks needed to get it to show more reliably? > I've > updated the code so that it should usually find it. But saving it here may > not be a big deal. Thanks, -- Marco
