[PATCH 1/1] perf/core: Require kernel access for text poke events

[Zhengchuan Liang]

Perf events with exclude_kernel=1 can be opened without kernel perf
access. However, exclude_kernel does not suppress text-poke sideband
records. Every PERF_RECORD_TEXT_POKE is marked PERF_RECORD_MISC_KERNEL
and contains a raw kernel instruction address.

An unprivileged task can therefore open and mmap a task-local software
event with text_poke=1. Both opening a count-only tracepoint event and
configuring UDP GRO for ESP-in-UDP cause updates to inline static calls;
the observer receives the relocated addresses of the modified instructions.
For a known kernel image, any such address reveals the runtime kernel
text base despite KASLR.

Call perf_allow_kernel() whenever attr.text_poke is set, regardless of
exclude_kernel. Events that neither monitor kernel execution nor request
text-poke records retain their existing permissions.

Fixes: e17d43b93e54 ("perf: Add perf text poke event")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Zhengchuan Liang <zcliangcn@xxxxxxxxx>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 634d2ccbab82..b4e6e8ae3be7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13953,7 +13953,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
-	if (!attr.exclude_kernel ||
+	if (!attr.exclude_kernel || attr.text_poke ||
 	    ((attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
 	     !attr.exclude_callchain_kernel)) {
 		err = perf_allow_kernel();
-- 
2.34.1