bpf: add lookup/update/delete/iterate methods to BPF maps

'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@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 281 insertions, 0 deletions

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 f58a10f9670c..395cabd2ca0a 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 */
+                __u32           map_fd;
+                __aligned_u64   key;
+                union {
+                        __aligned_u64 value;
+                        __aligned_u64 next_key;
+                };
+        };
 } __attribute__((aligned(8)));
 
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 428a0e23adc0..f94349ecaf61 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 +112,228 @@ 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;
+}
+
+/* helper to convert user pointers passed inside __aligned_u64 fields */
+static void __user *u64_to_ptr(__u64 val)
+{
+        return (void __user *) (unsigned long) val;
+}
+
+/* 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 = u64_to_ptr(attr->key);
+        void __user *uvalue = u64_to_ptr(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 = u64_to_ptr(attr->key);
+        void __user *uvalue = u64_to_ptr(attr->value);
+        int ufd = attr->map_fd;
+        struct fd f = fdget(ufd);
+        struct bpf_map *map;