diff mbox series

[bpf-next] bpf: Move out synchronize_rcu_tasks_trace from mutex CS

Message ID 20241231033509.349277-1-pulehui@huaweicloud.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series [bpf-next] bpf: Move out synchronize_rcu_tasks_trace from mutex CS | expand

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bpf/vmtest-bpf-next-PR success PR summary
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Commit Message

Pu Lehui Dec. 31, 2024, 3:35 a.m. UTC 
From: Pu Lehui <pulehui@huawei.com>

Commit ef1b808e3b7c ("bpf: Fix UAF via mismatching bpf_prog/attachment
RCU flavors") resolved a possible UAF issue in uprobes that attach
non-sleepable bpf prog by explicitly waiting for a tasks-trace-RCU grace
period. But, in the current implementation, synchronize_rcu_tasks_trace
is included within the mutex critical section, which increases the
length of the critical section and may affect performance. So let's move
out synchronize_rcu_tasks_trace from mutex CS.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
 kernel/trace/bpf_trace.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 48db147c6c7d..30ef8a6f5ca2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2245,12 +2245,15 @@  void perf_event_detach_bpf_prog(struct perf_event *event)
 {
 	struct bpf_prog_array *old_array;
 	struct bpf_prog_array *new_array;
+	struct bpf_prog *prog;
 	int ret;
 
 	mutex_lock(&bpf_event_mutex);
 
-	if (!event->prog)
-		goto unlock;
+	if (!event->prog) {
+		mutex_unlock(&bpf_event_mutex);
+		return;
+	}
 
 	old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
 	if (!old_array)
@@ -2265,6 +2268,11 @@  void perf_event_detach_bpf_prog(struct perf_event *event)
 	}
 
 put:
+	prog = event->prog;
+	event->prog = NULL;
+
+	mutex_unlock(&bpf_event_mutex);
+
 	/*
 	 * It could be that the bpf_prog is not sleepable (and will be freed
 	 * via normal RCU), but is called from a point that supports sleepable
@@ -2272,11 +2280,7 @@  void perf_event_detach_bpf_prog(struct perf_event *event)
 	 */
 	synchronize_rcu_tasks_trace();
 
-	bpf_prog_put(event->prog);
-	event->prog = NULL;
-
-unlock:
-	mutex_unlock(&bpf_event_mutex);
+	bpf_prog_put(prog);
 }
 
 int perf_event_query_prog_array(struct perf_event *event, void __user *info)