perf/bpf: Don't call bpf_overflow_handler() for tracing events

The regressing commit is new in 6.10. It assumed that anytime event->prog
is set bpf_overflow_handler() should be invoked to execute the attached bpf
program. This assumption is false for tracing events, and as a result the
regressing commit broke bpftrace by invoking the bpf handler with garbage
inputs on overflow.

Prior to the regression the overflow handlers formed a chain (of length 0,
1, or 2) and perf_event_set_bpf_handler() (the !tracing case) added
bpf_overflow_handler() to that chain, while perf_event_attach_bpf_prog()
(the tracing case) did not. Both set event->prog. The chain of overflow
handlers was replaced by a single overflow handler slot and a fixed call to
bpf_overflow_handler() when appropriate. This modifies the condition there
to check event->prog->type == BPF_PROG_TYPE_PERF_EVENT, restoring the
previous behavior and fixing bpftrace.

Signed-off-by: Kyle Huey <[email protected]>
Suggested-by: Andrii Nakryiko <[email protected]>
Reported-by: Joe Damato <[email protected]>
Closes: https://lore.kernel.org/lkml/ZpFfocvyF3KHaSzF@LQ3V64L9R2/
Fixes: f11f10b ("perf/bpf: Call BPF handler directly, not through overflow machinery")
Cc: [email protected]
Tested-by: Joe Damato <[email protected]> # bpftrace
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: khuey

kernel/events/core.c

@@ -9706,7 +9706,8 @@ static int __perf_event_overflow(struct perf_event *event,
 
 	ret = __perf_event_account_interrupt(event, throttle);
 
-	if (event->prog && !bpf_overflow_handler(event, data, regs))
+	if (event->prog && event->prog->type == BPF_PROG_TYPE_PERF_EVENT &&
+	    !bpf_overflow_handler(event, data, regs))
 		return ret;
 
 	/*