[PATCH 6.18.y 1/2] perf/core: Check kernel access when kernel callchains are requested

[Sasha Levin <sashal@kernel.org>]

From: Dapeng Mi <dapeng1.mi@linux.intel.com>

[ Upstream commit a4573a3838ae4fc73b70019cfa1dac9aaea7cc2f ]

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.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260616044654.3468742-9-dapeng1.mi@linux.intel.com
Stable-dep-of: 357e8a77a501 ("perf: Require kernel access for text poke events")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 d56ad3736e152..8f112f12cc3ce 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13536,7 +13536,9 @@ 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;
-- 
2.53.0