On 2024-10-28 13:42, Thomas Gleixner wrote:
On Mon, Sep 30 2024 at 15:23, Mathieu Desnoyers wrote:
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index a3d8ac00793e..0430890cbb42 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -303,6 +303,7 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
* Syscall probe called with preemption enabled, but the ring
* buffer and per-cpu data require preemption to be disabled.
*/
+ might_fault();
guard(preempt_notrace)();
I find it odd that the might_fault() check is in all the implementations
and not in the tracepoint itself:
if (syscall) {
might_fault();
rcu_read_unlock_trace();
} else ...
That's where I would have expected it to be.
You raise a good point: we should also add a might_fault() check in
__DO_TRACE() in the syscall case, so we can catch incorrect use of the
syscall tracepoint even if no probes are registered to it.
I've added the might_fault() in each tracer syscall probe to make sure
a tracer don't end up registering a faultable probe on a tracepoint
protected with preempt_disable by mistake. It validates that the tracers
are using the tracepoint registration as expected.
I'll prepare separate a patch adding this and will add it to this
series.
Thanks,
Mathieu
Thanks,
tglx
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
