[PATCH bpf 4/4] bpf: tracing: properly use bpf_prog_array api

[Stanislav Fomichev]

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.

Signed-off-by: Stanislav Fomichev <s...@google.com>
---
 kernel/trace/bpf_trace.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d64c00afceb5..5f8f7fdbe27c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -17,6 +17,9 @@
 #include "trace_probe.h"
 #include "trace.h"
 
+#define bpf_event_dereference(p)                                       \
+       rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
+
 #ifdef CONFIG_MODULES
 struct bpf_trace_module {
        struct module *module;
@@ -999,7 +1002,7 @@ 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;
 
@@ -1017,7 +1020,7 @@ 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_dereference(event->tp_event->prog_array);
        if (old_array &&
            bpf_prog_array_length(old_array) >= BPF_TRACE_MAX_PROGS) {
                ret = -E2BIG;
@@ -1040,7 +1043,7 @@ 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;
 
@@ -1049,7 +1052,7 @@ 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_dereference(event->tp_event->prog_array);
        ret = bpf_prog_array_copy(old_array, event->prog, NULL, &new_array);
        if (ret == -ENOENT)
                goto unlock;
@@ -1071,6 +1074,7 @@ 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;
 
@@ -1095,10 +1099,8 @@ 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_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)) ||
-- 
2.21.0.1020.gf2820cf01a-goog