[PATCH v4 2/4] bpf: Add new bpf map type to store the pointer to struct perf_event

[Kaixu Xia]

Introduce a new bpf map type 'BPF_MAP_TYPE_PERF_EVENT_ARRAY'.
This map only stores the pointer to struct perf_event. The
user space event FDs from perf_event_open() syscall are converted
to the pointer to struct perf_event and stored in map.

Signed-off-by: Kaixu Xia <xiakaixu@xxxxxxxxxx>
---
 include/linux/bpf.h        |  1 +
 include/linux/perf_event.h |  2 ++
 include/uapi/linux/bpf.h   |  1 +
 kernel/bpf/arraymap.c      | 57 ++++++++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/verifier.c      | 15 ++++++++++++
 kernel/events/core.c       | 17 ++++++++++++++
 6 files changed, 93 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 610b730..3c9c0eb 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -10,6 +10,7 @@
 #include <uapi/linux/bpf.h>
 #include <linux/workqueue.h>
 #include <linux/file.h>
+#include <linux/perf_event.h>
 
 struct bpf_map;
 
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2027809..2ea4067 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -641,6 +641,7 @@ extern int perf_event_init_task(struct task_struct *child);
 extern void perf_event_exit_task(struct task_struct *child);
 extern void perf_event_free_task(struct task_struct *task);
 extern void perf_event_delayed_put(struct task_struct *task);
+extern struct perf_event *perf_event_get(unsigned int fd);
 extern void perf_event_print_debug(void);
 extern void perf_pmu_disable(struct pmu *pmu);
 extern void perf_pmu_enable(struct pmu *pmu);
@@ -979,6 +980,7 @@ static inline int perf_event_init_task(struct task_struct *child)	{ return 0; }
 static inline void perf_event_exit_task(struct task_struct *child)	{ }
 static inline void perf_event_free_task(struct task_struct *task)	{ }
 static inline void perf_event_delayed_put(struct task_struct *task)	{ }
+static struct perf_event *perf_event_get(unsigned int fd)		{ return NULL; }
 static inline void perf_event_print_debug(void)				{ }
 static inline int perf_event_task_disable(void)				{ return -EINVAL; }
 static inline int perf_event_task_enable(void)				{ return -EINVAL; }
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 29ef6f9..69a1f6b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -114,6 +114,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_HASH,
 	BPF_MAP_TYPE_ARRAY,
 	BPF_MAP_TYPE_PROG_ARRAY,
+	BPF_MAP_TYPE_PERF_EVENT_ARRAY,
 };
 
 enum bpf_prog_type {
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 4784cdc..a9e0235 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -297,3 +297,60 @@ static int __init register_prog_array_map(void)
 	return 0;
 }
 late_initcall(register_prog_array_map);
+
+static void *perf_event_fd_array_get_ptr(struct bpf_array *array, int fd)
+{
+	struct perf_event *event;
+
+	event = perf_event_get(fd);
+	if (IS_ERR(event))
+		return event;
+
+	/*
+	 * prevent some crazy events so we can make our life easier
+	 */
+	if (event->attr.type != PERF_TYPE_RAW &&
+	    event->attr.type != PERF_TYPE_HARDWARE) {
+		perf_event_release_kernel(event);
+		return ERR_PTR(-EINVAL);
+	}
+	return event;
+}
+
+static void perf_event_fd_array_put_ptr(struct bpf_array *array, void *ptr)
+{
+	struct perf_event *event = (struct perf_event *)ptr;
+
+	perf_event_release_kernel(event);
+}
+
+static const struct fd_array_map_ops perf_event_fd_array_map_ops = {
+	.get_ptr	= perf_event_fd_array_get_ptr,
+	.put_ptr	= perf_event_fd_array_put_ptr,
+};
+
+static struct bpf_map *perf_event_array_map_alloc(union bpf_attr *attr)
+{
+	return fd_array_map_alloc(attr, &perf_event_fd_array_map_ops);
+}
+
+static const struct bpf_map_ops perf_event_array_ops = {
+	.map_alloc = perf_event_array_map_alloc,
+	.map_free = fd_array_map_free,
+	.map_get_next_key = array_map_get_next_key,
+	.map_lookup_elem = fd_array_map_lookup_elem,
+	.map_update_elem = fd_array_map_update_elem,
+	.map_delete_elem = fd_array_map_delete_elem,
+};
+
+static struct bpf_map_type_list perf_event_array_type __read_mostly = {
+	.ops = &perf_event_array_ops,
+	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
+};
+
+static int __init register_perf_event_array_map(void)
+{
+	bpf_register_map_type(&perf_event_array_type);
+	return 0;
+}
+late_initcall(register_perf_event_array_map);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 039d866..c70f7e7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -924,6 +924,21 @@ static int check_call(struct verifier_env *env, int func_id)
 		 */
 		return -EINVAL;
 
+	if (map && map->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY &&
+	    func_id != BPF_FUNC_perf_event_read)
+		/* perf_event_array map type needs extra care:
+		 * only allow to pass it into bpf_perf_event_read() for now.
+		 * bpf_map_update/delete_elem() must only be done via syscall
+		 */
+		return -EINVAL;
+
+	if (func_id == BPF_FUNC_perf_event_read &&
+	    map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
+		/* don't allow any other map type to be passed into
+		 * bpf_perf_event_read()
+		 */
+		return -EINVAL;
+
 	return 0;
 }
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d3dae34..58f0d47 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8574,6 +8574,23 @@ void perf_event_delayed_put(struct task_struct *task)
 		WARN_ON_ONCE(task->perf_event_ctxp[ctxn]);
 }
 
+struct perf_event *perf_event_get(unsigned int fd)
+{
+	int err;
+	struct fd f;
+	struct perf_event *event;
+
+	err = perf_fget_light(fd, &f);
+	if (err)
+		return ERR_PTR(err);
+
+	event = f.file->private_data;
+	atomic_long_inc(&event->refcount);
+	fdput(f);
+
+	return event;
+}
+
 /*
  * inherit a event from parent task to child task:
  */
-- 
1.8.3.4

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