tracepoint: Add tracepoint_probe_register_may_exist() for BPF tracing

commit 9913d57 upstream.

All internal use cases for tracepoint_probe_register() is set to not ever
be called with the same function and data. If it is, it is considered a
bug, as that means the accounting of handling tracepoints is corrupted.
If the function and data for a tracepoint is already registered when
tracepoint_probe_register() is called, it will call WARN_ON_ONCE() and
return with EEXISTS.

The BPF system call can end up calling tracepoint_probe_register() with
the same data, which now means that this can trigger the warning because
of a user space process. As WARN_ON_ONCE() should not be called because
user space called a system call with bad data, there needs to be a way to
register a tracepoint without triggering a warning.

Enter tracepoint_probe_register_may_exist(), which can be called, but will
not cause a WARN_ON() if the probe already exists. It will still error out
with EEXIST, which will then be sent to the user space that performed the
BPF system call.

This keeps the previous testing for issues with other users of the
tracepoint code, while letting BPF call it with duplicated data and not
warn about it.

Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://syzkaller.appspot.com/bug?id=41f4318cf01762389f4d1c1c459da4f542fe5153

Cc: [email protected]
Fixes: c4f6699 ("bpf: introduce BPF_RAW_TRACEPOINT")
Reported-by: syzbot <[email protected]>
Reported-by: Tetsuo Handa <[email protected]>
Tested-by: [email protected]
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: rostedt

include/linux/tracepoint.h

@@ -41,7 +41,17 @@ extern int
 tracepoint_probe_register_prio(struct tracepoint *tp, void *probe, void *data,
 			       int prio);
 extern int
+tracepoint_probe_register_prio_may_exist(struct tracepoint *tp, void *probe, void *data,
+					 int prio);
+extern int
 tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data);
+static inline int
+tracepoint_probe_register_may_exist(struct tracepoint *tp, void *probe,
+				    void *data)
+{
+	return tracepoint_probe_register_prio_may_exist(tp, probe, data,
+							TRACEPOINT_DEFAULT_PRIO);
+}
 extern void
 for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
 		void *priv);

kernel/trace/bpf_trace.c

@@ -2143,7 +2143,8 @@ static int __bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *
 	if (prog->aux->max_tp_access > btp->writable_size)
 		return -EINVAL;
 
-	return tracepoint_probe_register(tp, (void *)btp->bpf_func, prog);
+	return tracepoint_probe_register_may_exist(tp, (void *)btp->bpf_func,
+						   prog);
 }
 
 int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog)

kernel/tracepoint.c

@@ -273,7 +273,8 @@ static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func
  * Add the probe function to a tracepoint.
  */
 static int tracepoint_add_func(struct tracepoint *tp,
-			       struct tracepoint_func *func, int prio)
+			       struct tracepoint_func *func, int prio,
+			       bool warn)
 {
 	struct tracepoint_func *old, *tp_funcs;
 	int ret;
@@ -288,7 +289,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func, prio);
 	if (IS_ERR(old)) {
-		WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
+		WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}
 
@@ -343,6 +344,32 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 	return 0;
 }
 
+/**
+ * tracepoint_probe_register_prio_may_exist -  Connect a probe to a tracepoint with priority
+ * @tp: tracepoint
+ * @probe: probe handler
+ * @data: tracepoint data
+ * @prio: priority of this function over other registered functions
+ *
+ * Same as tracepoint_probe_register_prio() except that it will not warn
+ * if the tracepoint is already registered.
+ */
+int tracepoint_probe_register_prio_may_exist(struct tracepoint *tp, void *probe,
+					     void *data, int prio)
+{
+	struct tracepoint_func tp_func;
+	int ret;
+
+	mutex_lock(&tracepoints_mutex);
+	tp_func.func = probe;
+	tp_func.data = data;
+	tp_func.prio = prio;
+	ret = tracepoint_add_func(tp, &tp_func, prio, false);
+	mutex_unlock(&tracepoints_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio_may_exist);
+
 /**
  * tracepoint_probe_register_prio -  Connect a probe to a tracepoint with priority
  * @tp: tracepoint
@@ -366,7 +393,7 @@ int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
 	tp_func.func = probe;
 	tp_func.data = data;
 	tp_func.prio = prio;
-	ret = tracepoint_add_func(tp, &tp_func, prio);
+	ret = tracepoint_add_func(tp, &tp_func, prio, true);
 	mutex_unlock(&tracepoints_mutex);
 	return ret;
 }