signal, perf: Add missing TRAP_PERF case in siginfo_layout()

Add the missing TRAP_PERF case in siginfo_layout() for interpreting the
layout correctly as SIL_PERF_EVENT instead of just SIL_FAULT. This
ensures the si_perf field is copied and not just the si_addr field.

This was caught and tested by running the perf_events/sigtrap_threads
kselftest as a 32-bit binary with a 64-bit kernel.

Fixes: fb6cc127 ("signal: Introduce TRAP_PERF si_code and si_perf to siginfo")
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210422191823.79012-2-elver@google.com

kernel/signal.c

@@ -3206,6 +3206,8 @@ enum siginfo_layout siginfo_layout(unsigned sig, int si_code)
 			else if ((sig == SIGSEGV) && (si_code == SEGV_PKUERR))
 				layout = SIL_FAULT_PKUERR;
 #endif
+			else if ((sig == SIGTRAP) && (si_code == TRAP_PERF))
+				layout = SIL_PERF_EVENT;
 		}
 		else if (si_code <= NSIGPOLL)
 			layout = SIL_POLL;