Re: [PATCH v3 1/2] tracing: Add task_prctl_unknown tracepoint

[Alexander Potapenko]

On Fri, Nov 8, 2024 at 12:35 PM 'Marco Elver' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> 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:
>
>   test-380     [001] .....    78.142904: task_prctl_unknown: option=1234 arg2=101 arg3=102 arg4=103 arg5=104

For what it's worth:

> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>