bpf: tracing: properly use bpf_prog_array api

Now that we don't have __rcu markers on the bpf_prog_array helpers,
let's use proper rcu_dereference_protected to obtain array pointer
under mutex.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/trace/bpf_trace.c

@@ -19,6 +19,9 @@
 #include "trace_probe.h"
 #include "trace.h"
 
+#define bpf_event_rcu_dereference(p)					\
+	rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
+
 #ifdef CONFIG_MODULES
 struct bpf_trace_module {
 	struct module *module;
@@ -1099,7 +1102,7 @@ static DEFINE_MUTEX(bpf_event_mutex);
 int perf_event_attach_bpf_prog(struct perf_event *event,
 			       struct bpf_prog *prog)
 {
-	struct bpf_prog_array __rcu *old_array;
+	struct bpf_prog_array *old_array;
 	struct bpf_prog_array *new_array;
 	int ret = -EEXIST;
 
@@ -1117,7 +1120,7 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
 	if (event->prog)
 		goto unlock;
 
-	old_array = event->tp_event->prog_array;
+	old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
 	if (old_array &&
 	    bpf_prog_array_length(old_array) >= BPF_TRACE_MAX_PROGS) {
 		ret = -E2BIG;
@@ -1140,7 +1143,7 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
 
 void perf_event_detach_bpf_prog(struct perf_event *event)
 {
-	struct bpf_prog_array __rcu *old_array;
+	struct bpf_prog_array *old_array;
 	struct bpf_prog_array *new_array;
 	int ret;
 
@@ -1149,7 +1152,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
 	if (!event->prog)
 		goto unlock;
 
-	old_array = event->tp_event->prog_array;
+	old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
 	ret = bpf_prog_array_copy(old_array, event->prog, NULL, &new_array);
 	if (ret == -ENOENT)
 		goto unlock;
@@ -1171,6 +1174,7 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
 {
 	struct perf_event_query_bpf __user *uquery = info;
 	struct perf_event_query_bpf query = {};
+	struct bpf_prog_array *progs;
 	u32 *ids, prog_cnt, ids_len;
 	int ret;
 
@@ -1195,10 +1199,8 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
 	 */
 
 	mutex_lock(&bpf_event_mutex);
-	ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
-				       ids,
-				       ids_len,
-				       &prog_cnt);
+	progs = bpf_event_rcu_dereference(event->tp_event->prog_array);
+	ret = bpf_prog_array_copy_info(progs, ids, ids_len, &prog_cnt);
 	mutex_unlock(&bpf_event_mutex);
 
 	if (copy_to_user(&uquery->prog_cnt, &prog_cnt, sizeof(prog_cnt)) ||