[PATCH v12 net-next 03/11] bpf: add lookup/update/delete/iterate methods to BPF maps

From: Alexei Starovoitov
Date: Mon Sep 15 2014 - 15:22:33 EST


'maps' is a generic storage of different types for sharing data between kernel
and userspace.

The maps are accessed from user space via BPF syscall, which has commands:

- create a map with given type and attributes
fd = bpf(BPF_MAP_CREATE, union bpf_attr *attr, u32 size)
returns fd or negative error

- lookup key in a given map referenced by fd
err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)
using attr->map_fd, attr->key, attr->value
returns zero and stores found elem into value or negative error

- create or update key/value pair in a given map
err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)
using attr->map_fd, attr->key, attr->value
returns zero or negative error

- find and delete element by key in a given map
err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)
using attr->map_fd, attr->key

- iterate map elements (based on input key return next_key)
err = bpf(BPF_MAP_GET_NEXT_KEY, union bpf_attr *attr, u32 size)
using attr->map_fd, attr->key, attr->next_key

- close(fd) deletes the map

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
---
include/linux/bpf.h | 8 ++
include/uapi/linux/bpf.h | 38 ++++++++
kernel/bpf/syscall.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 275 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 48014a71f0fe..2887f3f9da59 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -9,6 +9,7 @@

#include <uapi/linux/bpf.h>
#include <linux/workqueue.h>
+#include <linux/file.h>

struct bpf_map;

@@ -17,6 +18,12 @@ struct bpf_map_ops {
/* funcs callable from userspace (via syscall) */
struct bpf_map *(*map_alloc)(union bpf_attr *attr);
void (*map_free)(struct bpf_map *);
+ int (*map_get_next_key)(struct bpf_map *map, void *key, void *next_key);
+
+ /* funcs callable from userspace and from eBPF programs */
+ void *(*map_lookup_elem)(struct bpf_map *map, void *key);
+ int (*map_update_elem)(struct bpf_map *map, void *key, void *value);
+ int (*map_delete_elem)(struct bpf_map *map, void *key);
};

struct bpf_map {
@@ -37,5 +44,6 @@ struct bpf_map_type_list {

void bpf_register_map_type(struct bpf_map_type_list *tl);
void bpf_map_put(struct bpf_map *map);
+struct bpf_map *bpf_map_get(struct fd f);

#endif /* _LINUX_BPF_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ecc8fa48a2a4..d4ba8bb66bd4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -70,6 +70,35 @@ enum bpf_cmd {
* map is deleted when fd is closed
*/
BPF_MAP_CREATE,
+
+ /* lookup key in a given map
+ * err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)
+ * Using attr->map_fd, attr->key, attr->value
+ * returns zero and stores found elem into value
+ * or negative error
+ */
+ BPF_MAP_LOOKUP_ELEM,
+
+ /* create or update key/value pair in a given map
+ * err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)
+ * Using attr->map_fd, attr->key, attr->value
+ * returns zero or negative error
+ */
+ BPF_MAP_UPDATE_ELEM,
+
+ /* find and delete elem by key in a given map
+ * err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)
+ * Using attr->map_fd, attr->key
+ * returns zero or negative error
+ */
+ BPF_MAP_DELETE_ELEM,
+
+ /* lookup key in a given map and return next key
+ * err = bpf(BPF_MAP_GET_NEXT_KEY, union bpf_attr *attr, u32 size)
+ * Using attr->map_fd, attr->key, attr->next_key
+ * returns zero and stores next key or negative error
+ */
+ BPF_MAP_GET_NEXT_KEY,
};

enum bpf_map_type {
@@ -83,6 +112,15 @@ union bpf_attr {
__u32 value_size; /* size of value in bytes */
__u32 max_entries; /* max number of entries in a map */
};
+
+ struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
+ int map_fd;
+ void __user *key;
+ union {
+ void __user *value;
+ void __user *next_key;
+ };
+ };
};

#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 80082ec5a5fc..fdf7bd79cf76 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -13,6 +13,7 @@
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/anon_inodes.h>
+#include <linux/file.h>

static LIST_HEAD(bpf_map_types);

@@ -111,6 +112,222 @@ free_map:
return err;
}

+/* if error is returned, fd is released.
+ * On success caller should complete fd access with matching fdput()
+ */
+struct bpf_map *bpf_map_get(struct fd f)
+{
+ struct bpf_map *map;
+
+ if (!f.file)
+ return ERR_PTR(-EBADF);
+
+ if (f.file->f_op != &bpf_map_fops) {
+ fdput(f);
+ return ERR_PTR(-EINVAL);
+ }
+
+ map = f.file->private_data;
+
+ return map;
+}
+
+/* last field in 'union bpf_attr' used by this command */
+#define BPF_MAP_LOOKUP_ELEM_LAST_FIELD value
+
+static int map_lookup_elem(union bpf_attr *attr)
+{
+ void __user *ukey = attr->key;
+ void __user *uvalue = attr->value;
+ int ufd = attr->map_fd;
+ struct fd f = fdget(ufd);
+ struct bpf_map *map;
+ void *key, *value;
+ int err;
+
+ if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
+ return -EINVAL;
+
+ map = bpf_map_get(f);
+ if (IS_ERR(map))
+ return PTR_ERR(map);
+
+ err = -ENOMEM;
+ key = kmalloc(map->key_size, GFP_USER);
+ if (!key)
+ goto err_put;
+
+ err = -EFAULT;
+ if (copy_from_user(key, ukey, map->key_size) != 0)
+ goto free_key;
+
+ err = -ESRCH;
+ rcu_read_lock();
+ value = map->ops->map_lookup_elem(map, key);
+ if (!value)
+ goto err_unlock;
+
+ err = -EFAULT;
+ if (copy_to_user(uvalue, value, map->value_size) != 0)
+ goto err_unlock;
+
+ err = 0;
+
+err_unlock:
+ rcu_read_unlock();
+free_key:
+ kfree(key);
+err_put:
+ fdput(f);
+ return err;
+}
+
+#define BPF_MAP_UPDATE_ELEM_LAST_FIELD value
+
+static int map_update_elem(union bpf_attr *attr)
+{
+ void __user *ukey = attr->key;
+ void __user *uvalue = attr->value;
+ int ufd = attr->map_fd;
+ struct fd f = fdget(ufd);
+ struct bpf_map *map;
+ void *key, *value;
+ int err;
+
+ if (CHECK_ATTR(BPF_MAP_UPDATE_ELEM))
+ return -EINVAL;
+
+ map = bpf_map_get(f);
+ if (IS_ERR(map))
+ return PTR_ERR(map);
+
+ err = -ENOMEM;
+ key = kmalloc(map->key_size, GFP_USER);
+ if (!key)
+ goto err_put;
+
+ err = -EFAULT;
+ if (copy_from_user(key, ukey, map->key_size) != 0)
+ goto free_key;
+
+ err = -ENOMEM;
+ value = kmalloc(map->value_size, GFP_USER);
+ if (!value)
+ goto free_key;
+
+ err = -EFAULT;
+ if (copy_from_user(value, uvalue, map->value_size) != 0)
+ goto free_value;
+
+ /* eBPF program that use maps are running under rcu_read_lock(),
+ * therefore all map accessors rely on this fact, so do the same here
+ */
+ rcu_read_lock();
+ err = map->ops->map_update_elem(map, key, value);
+ rcu_read_unlock();
+
+free_value:
+ kfree(value);
+free_key:
+ kfree(key);
+err_put:
+ fdput(f);
+ return err;
+}
+
+#define BPF_MAP_DELETE_ELEM_LAST_FIELD key
+
+static int map_delete_elem(union bpf_attr *attr)
+{
+ void __user *ukey = attr->key;
+ int ufd = attr->map_fd;
+ struct fd f = fdget(ufd);
+ struct bpf_map *map;
+ void *key;
+ int err;
+
+ if (CHECK_ATTR(BPF_MAP_DELETE_ELEM))
+ return -EINVAL;
+
+ map = bpf_map_get(f);
+ if (IS_ERR(map))
+ return PTR_ERR(map);
+
+ err = -ENOMEM;
+ key = kmalloc(map->key_size, GFP_USER);
+ if (!key)
+ goto err_put;
+
+ err = -EFAULT;
+ if (copy_from_user(key, ukey, map->key_size) != 0)
+ goto free_key;
+
+ rcu_read_lock();
+ err = map->ops->map_delete_elem(map, key);
+ rcu_read_unlock();
+
+free_key:
+ kfree(key);
+err_put:
+ fdput(f);
+ return err;
+}
+
+/* last field in 'union bpf_attr' used by this command */
+#define BPF_MAP_GET_NEXT_KEY_LAST_FIELD next_key
+
+static int map_get_next_key(union bpf_attr *attr)
+{
+ void __user *ukey = attr->key;
+ void __user *unext_key = attr->next_key;
+ int ufd = attr->map_fd;
+ struct fd f = fdget(ufd);
+ struct bpf_map *map;
+ void *key, *next_key;
+ int err;
+
+ if (CHECK_ATTR(BPF_MAP_GET_NEXT_KEY))
+ return -EINVAL;
+
+ map = bpf_map_get(f);
+ if (IS_ERR(map))
+ return PTR_ERR(map);
+
+ err = -ENOMEM;
+ key = kmalloc(map->key_size, GFP_USER);
+ if (!key)
+ goto err_put;
+
+ err = -EFAULT;
+ if (copy_from_user(key, ukey, map->key_size) != 0)
+ goto free_key;
+
+ err = -ENOMEM;
+ next_key = kmalloc(map->key_size, GFP_USER);
+ if (!next_key)
+ goto free_key;
+
+ rcu_read_lock();
+ err = map->ops->map_get_next_key(map, key, next_key);
+ rcu_read_unlock();
+ if (err)
+ goto free_next_key;
+
+ err = -EFAULT;
+ if (copy_to_user(unext_key, next_key, map->key_size) != 0)
+ goto free_next_key;
+
+ err = 0;
+
+free_next_key:
+ kfree(next_key);
+free_key:
+ kfree(key);
+err_put:
+ fdput(f);
+ return err;
+}
+
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
union bpf_attr *attr;
@@ -140,6 +357,18 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_MAP_CREATE:
err = map_create(attr);
break;
+ case BPF_MAP_LOOKUP_ELEM:
+ err = map_lookup_elem(attr);
+ break;
+ case BPF_MAP_UPDATE_ELEM:
+ err = map_update_elem(attr);
+ break;
+ case BPF_MAP_DELETE_ELEM:
+ err = map_delete_elem(attr);
+ break;
+ case BPF_MAP_GET_NEXT_KEY:
+ err = map_get_next_key(attr);
+ break;
default:
err = -EINVAL;
break;
--
1.7.9.5

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