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
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/r/20241108113455.2924361-1-elver@google.com
Signed-off-by: Kees Cook <kees@kernel.org>
c38904ebb7