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[PATCH v2 3/5] bpf: Save the pointer to struct perf_event to map

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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@huawei.com>
---
 include/linux/perf_event.h |  2 ++
 kernel/bpf/arraymap.c      | 53 ++++++++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c       | 26 +++++++++++++++++++++++
 kernel/events/core.c       | 26 +++++++++++++++++++++++
 4 files changed, 107 insertions(+)

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/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 410bc40..a7475ae 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/mm.h>
 #include <linux/filter.h>
+#include <linux/perf_event.h>
 
 /* Called from syscall */
 static struct bpf_map *array_map_alloc(union bpf_attr *attr)
@@ -276,6 +277,57 @@ static int perf_event_array_map_get_next_key(struct bpf_map *map, void *key,
 	return -EINVAL;
 }
 
+static int replace_map_with_perf_event(void *value)
+{
+	struct perf_event *event;
+	u32 fd;
+
+	fd = *(u32 *)value;
+
+	event = perf_event_get(fd);
+	if (IS_ERR(event))
+		return PTR_ERR(event);
+
+	/* limit the event type to PERF_TYPE_RAW
+	 * and PERF_TYPE_HARDWARE
+	 */
+	if (event->attr.type != PERF_TYPE_RAW &&
+	    event->attr.type != PERF_TYPE_HARDWARE)
+		return -EINVAL;
+
+	memcpy(value, &event, sizeof(struct perf_event *));
+
+	return 0;
+}
+
+static bool check_map_perf_event_stored(struct bpf_map *map, void *key)
+{
+	void *event;
+	bool is_stored = false;
+
+	rcu_read_lock();
+	event = array_map_lookup_elem(map, key);
+	if (event && (*(unsigned long *)event))
+		is_stored = true;
+	rcu_read_unlock();
+
+	return is_stored;
+}
+
+/* only called from syscall */
+static int perf_event_array_map_update_elem(struct bpf_map *map, void *key,
+					    void *value, u64 map_flags)
+{
+	/* check if the value is already stored */
+	if (check_map_perf_event_stored(map, key))
+		return -EINVAL;
+
+	if (replace_map_with_perf_event(value))
+		return -EBADF;
+
+	return array_map_update_elem(map, key, value, map_flags);
+}
+
 static int perf_event_array_map_traverse_elem(bpf_map_traverse_callback func,
 					      struct bpf_map *map)
 {
@@ -297,6 +349,7 @@ static const struct bpf_map_ops perf_event_array_ops = {
 	.map_free = array_map_free,
 	.map_get_next_key = perf_event_array_map_get_next_key,
 	.map_lookup_elem = array_map_lookup_elem,
+	.map_update_elem = perf_event_array_map_update_elem,
 	.map_delete_elem = array_map_delete_elem,
 	.map_traverse_elem = perf_event_array_map_traverse_elem,
 };
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a1b14d1..854f351 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -17,6 +17,7 @@
 #include <linux/license.h>
 #include <linux/filter.h>
 #include <linux/version.h>
+#include <linux/perf_event.h>
 
 static LIST_HEAD(bpf_map_types);
 
@@ -64,6 +65,19 @@ void bpf_map_put(struct bpf_map *map)
 	}
 }
 
+static int bpf_map_perf_event_put(void *value)
+{
+	struct perf_event *event;
+
+	event = (struct perf_event *)(*(unsigned long *)value);
+	if (!event)
+		return -EBADF;
+
+	perf_event_release_kernel(event);
+
+	return 0;
+}
+
 static int bpf_map_release(struct inode *inode, struct file *filp)
 {
 	struct bpf_map *map = filp->private_data;
@@ -74,6 +88,18 @@ static int bpf_map_release(struct inode *inode, struct file *filp)
 		 */
 		bpf_prog_array_map_clear(map);
 
+	if (map->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
+		if (!map->ops->map_traverse_elem)
+			return -EPERM;
+
+		rcu_read_lock();
+		if (map->ops->map_traverse_elem(bpf_map_perf_event_put, map) < 0) {
+			rcu_read_unlock();
+			return -EINVAL;
+		}
+		rcu_read_unlock();
+	}
+
 	bpf_map_put(map);
 	return 0;
 }
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d3dae34..14a9924 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8574,6 +8574,32 @@ 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)
+{
+	struct perf_event *event;
+	struct fd f;
+
+	f = fdget(fd);
+
+	if (!f.file)
+		return ERR_PTR(-EBADF);
+
+	if (f.file->f_op != &perf_fops) {
+		fdput(f);
+		return ERR_PTR(-EINVAL);
+	}
+
+	event = f.file->private_data;
+
+	if (!atomic_long_inc_not_zero(&event->refcount)) {
+		fdput(f);
+		return ERR_PTR(-ENOENT);
+	}
+
+	fdput(f);
+	return event;
+}
+
 /*
  * inherit a event from parent task to child task:
  */
-- 
1.8.3.4

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[PATCH v2 3/5] bpf: Save the pointer to struct perf_event to map Kaixu Xia <xiakaixu@huawei.com> - 2015-07-22 10:20 +0200

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