[Patch v3 8/8] perf/core: Check kernel access when kernel callchains are requested

[Dapeng Mi]

perf_event_open() currently gates perf_allow_kernel() only on
!attr.exclude_kernel.

However, users can still request kernel callchain collection with
attr.exclude_callchain_kernel == 0 even when attr.exclude_kernel == 1.
That still requires kernel profiling privilege, but the existing check
does not enforce it.

Update the permission check to call perf_allow_kernel() when either
kernel sampling is requested or kernel callchains are requested.

This keeps permission checks aligned with requested data and prevents
unprivileged use of kernel callchain capture.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 kernel/events/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 89f6c9ffb964..bbd260d9d5b5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13924,7 +13924,9 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
-	if (!attr.exclude_kernel) {
+	if (!attr.exclude_kernel ||
+	    ((attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
+	     !attr.exclude_callchain_kernel)) {
 		err = perf_allow_kernel();
 		if (err)
 			return err;
-- 
2.34.1