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bpf: add lookup/update/delete/iterate methods to BPF maps
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'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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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Alexei Starovoitov authored and davem330 committed Sep 26, 2014
1 parent 749730c commit db20fd2
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8 changes: 8 additions & 0 deletions include/linux/bpf.h
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@

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

struct bpf_map;

Expand All @@ -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 {
Expand All @@ -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 */
38 changes: 38 additions & 0 deletions include/uapi/linux/bpf.h
Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand All @@ -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__ */
235 changes: 235 additions & 0 deletions kernel/bpf/syscall.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);

Expand Down Expand Up @@ -111,6 +112,228 @@ static int map_create(union bpf_attr *attr)
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;
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 = u64_to_ptr(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 = u64_to_ptr(attr->key);
void __user *unext_key = u64_to_ptr(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 = {};
Expand Down Expand Up @@ -160,6 +383,18 @@ 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;
Expand Down

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