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

Kaixu Xia
2015-07-22T08:12:49Z

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