kernel/bpf/hashtab.c

   1 /* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of version 2 of the GNU General Public
   5  * License as published by the Free Software Foundation.
   6  *
   7  * This program is distributed in the hope that it will be useful, but
   8  * WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  10  * General Public License for more details.
  11  */
  12 #include <linux/bpf.h>
  13 #include <linux/jhash.h>
  14 #include <linux/filter.h>
  15 #include <linux/vmalloc.h>
  16
  17 struct bpf_htab {
  18         struct bpf_map map;
  19         struct hlist_head *buckets;
  20         spinlock_t lock;
  21         u32 count;      /* number of elements in this hashtable */
  22         u32 n_buckets;  /* number of hash buckets */
  23         u32 elem_size;  /* size of each element in bytes */
  24 };
  25
  26 /* each htab element is struct htab_elem + key + value */
  27 struct htab_elem {
  28         struct hlist_node hash_node;
  29         struct rcu_head rcu;
  30         u32 hash;
  31         char key[0] __aligned(8);
  32 };
  33
  34 /* Called from syscall */
  35 static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
  36 {
  37         struct bpf_htab *htab;
  38         int err, i;
  39
  40         htab = kzalloc(sizeof(*htab), GFP_USER);
  41         if (!htab)
  42                 return ERR_PTR(-ENOMEM);
  43
  44         /* mandatory map attributes */
  45         htab->map.key_size = attr->key_size;
  46         htab->map.value_size = attr->value_size;
  47         htab->map.max_entries = attr->max_entries;
  48
  49         /* check sanity of attributes.
  50          * value_size == 0 may be allowed in the future to use map as a set
  51          */
  52         err = -EINVAL;
  53         if (htab->map.max_entries == 0 || htab->map.key_size == 0 ||
  54             htab->map.value_size == 0)
  55                 goto free_htab;
  56
  57         /* hash table size must be power of 2 */
  58         htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
  59
  60         err = -E2BIG;
  61         if (htab->map.key_size > MAX_BPF_STACK)
  62                 /* eBPF programs initialize keys on stack, so they cannot be
  63                  * larger than max stack size
  64                  */
  65                 goto free_htab;
  66
  67         err = -ENOMEM;
  68         /* prevent zero size kmalloc and check for u32 overflow */
  69         if (htab->n_buckets == 0 ||
  70             htab->n_buckets > U32_MAX / sizeof(struct hlist_head))
  71                 goto free_htab;
  72
  73         htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
  74                                       GFP_USER | __GFP_NOWARN);
  75
  76         if (!htab->buckets) {
  77                 htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
  78                 if (!htab->buckets)
  79                         goto free_htab;
  80         }
  81
  82         for (i = 0; i < htab->n_buckets; i++)
  83                 INIT_HLIST_HEAD(&htab->buckets[i]);
  84
  85         spin_lock_init(&htab->lock);
  86         htab->count = 0;
  87
  88         htab->elem_size = sizeof(struct htab_elem) +
  89                           round_up(htab->map.key_size, 8) +
  90                           htab->map.value_size;
  91         return &htab->map;
  92
  93 free_htab:
  94         kfree(htab);
  95         return ERR_PTR(err);
  96 }
  97
  98 static inline u32 htab_map_hash(const void *key, u32 key_len)
  99 {
 100         return jhash(key, key_len, 0);
 101 }
 102
 103 static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
 104 {
 105         return &htab->buckets[hash & (htab->n_buckets - 1)];
 106 }
 107
 108 static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
 109                                          void *key, u32 key_size)
 110 {
 111         struct htab_elem *l;
 112
 113         hlist_for_each_entry_rcu(l, head, hash_node)
 114                 if (l->hash == hash && !memcmp(&l->key, key, key_size))
 115                         return l;
 116
 117         return NULL;
 118 }
 119
 120 /* Called from syscall or from eBPF program */
 121 static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
 122 {
 123         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 124         struct hlist_head *head;
 125         struct htab_elem *l;
 126         u32 hash, key_size;
 127
 128         /* Must be called with rcu_read_lock. */
 129         WARN_ON_ONCE(!rcu_read_lock_held());
 130
 131         key_size = map->key_size;
 132
 133         hash = htab_map_hash(key, key_size);
 134
 135         head = select_bucket(htab, hash);
 136
 137         l = lookup_elem_raw(head, hash, key, key_size);
 138
 139         if (l)
 140                 return l->key + round_up(map->key_size, 8);
 141
 142         return NULL;
 143 }
 144
 145 /* Called from syscall */
 146 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
 147 {
 148         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 149         struct hlist_head *head;
 150         struct htab_elem *l, *next_l;
 151         u32 hash, key_size;
 152         int i;
 153
 154         WARN_ON_ONCE(!rcu_read_lock_held());
 155
 156         key_size = map->key_size;
 157
 158         hash = htab_map_hash(key, key_size);
 159
 160         head = select_bucket(htab, hash);
 161
 162         /* lookup the key */
 163         l = lookup_elem_raw(head, hash, key, key_size);
 164
 165         if (!l) {
 166                 i = 0;
 167                 goto find_first_elem;
 168         }
 169
 170         /* key was found, get next key in the same bucket */
 171         next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
 172                                   struct htab_elem, hash_node);
 173
 174         if (next_l) {
 175                 /* if next elem in this hash list is non-zero, just return it */
 176                 memcpy(next_key, next_l->key, key_size);
 177                 return 0;
 178         }
 179
 180         /* no more elements in this hash list, go to the next bucket */
 181         i = hash & (htab->n_buckets - 1);
 182         i++;
 183
 184 find_first_elem:
 185         /* iterate over buckets */
 186         for (; i < htab->n_buckets; i++) {
 187                 head = select_bucket(htab, i);
 188
 189                 /* pick first element in the bucket */
 190                 next_l = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
 191                                           struct htab_elem, hash_node);
 192                 if (next_l) {
 193                         /* if it's not empty, just return it */
 194                         memcpy(next_key, next_l->key, key_size);
 195                         return 0;
 196                 }
 197         }
 198
 199         /* itereated over all buckets and all elements */
 200         return -ENOENT;
 201 }
 202
 203 /* Called from syscall or from eBPF program */
 204 static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 205                                 u64 map_flags)
 206 {
 207         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 208         struct htab_elem *l_new, *l_old;
 209         struct hlist_head *head;
 210         unsigned long flags;
 211         u32 key_size;
 212         int ret;
 213
 214         if (map_flags > BPF_EXIST)
 215                 /* unknown flags */
 216                 return -EINVAL;
 217
 218         WARN_ON_ONCE(!rcu_read_lock_held());
 219
 220         /* allocate new element outside of lock */
 221         l_new = kmalloc(htab->elem_size, GFP_ATOMIC);
 222         if (!l_new)
 223                 return -ENOMEM;
 224
 225         key_size = map->key_size;
 226
 227         memcpy(l_new->key, key, key_size);
 228         memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);
 229
 230         l_new->hash = htab_map_hash(l_new->key, key_size);
 231
 232         /* bpf_map_update_elem() can be called in_irq() */
 233         spin_lock_irqsave(&htab->lock, flags);
 234
 235         head = select_bucket(htab, l_new->hash);
 236
 237         l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
 238
 239         if (!l_old && unlikely(htab->count >= map->max_entries)) {
 240                 /* if elem with this 'key' doesn't exist and we've reached
 241                  * max_entries limit, fail insertion of new elem
 242                  */
 243                 ret = -E2BIG;
 244                 goto err;
 245         }
 246
 247         if (l_old && map_flags == BPF_NOEXIST) {
 248                 /* elem already exists */
 249                 ret = -EEXIST;
 250                 goto err;
 251         }
 252
 253         if (!l_old && map_flags == BPF_EXIST) {
 254                 /* elem doesn't exist, cannot update it */
 255                 ret = -ENOENT;
 256                 goto err;
 257         }
 258
 259         /* add new element to the head of the list, so that concurrent
 260          * search will find it before old elem
 261          */
 262         hlist_add_head_rcu(&l_new->hash_node, head);
 263         if (l_old) {
 264                 hlist_del_rcu(&l_old->hash_node);
 265                 kfree_rcu(l_old, rcu);
 266         } else {
 267                 htab->count++;
 268         }
 269         spin_unlock_irqrestore(&htab->lock, flags);
 270
 271         return 0;
 272 err:
 273         spin_unlock_irqrestore(&htab->lock, flags);
 274         kfree(l_new);
 275         return ret;
 276 }
 277
 278 /* Called from syscall or from eBPF program */
 279 static int htab_map_delete_elem(struct bpf_map *map, void *key)
 280 {
 281         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 282         struct hlist_head *head;
 283         struct htab_elem *l;
 284         unsigned long flags;
 285         u32 hash, key_size;
 286         int ret = -ENOENT;
 287
 288         WARN_ON_ONCE(!rcu_read_lock_held());
 289
 290         key_size = map->key_size;
 291
 292         hash = htab_map_hash(key, key_size);
 293
 294         spin_lock_irqsave(&htab->lock, flags);
 295
 296         head = select_bucket(htab, hash);
 297
 298         l = lookup_elem_raw(head, hash, key, key_size);
 299
 300         if (l) {
 301                 hlist_del_rcu(&l->hash_node);
 302                 htab->count--;
 303                 kfree_rcu(l, rcu);
 304                 ret = 0;
 305         }
 306
 307         spin_unlock_irqrestore(&htab->lock, flags);
 308         return ret;
 309 }
 310
 311 static void delete_all_elements(struct bpf_htab *htab)
 312 {
 313         int i;
 314
 315         for (i = 0; i < htab->n_buckets; i++) {
 316                 struct hlist_head *head = select_bucket(htab, i);
 317                 struct hlist_node *n;
 318                 struct htab_elem *l;
 319
 320                 hlist_for_each_entry_safe(l, n, head, hash_node) {
 321                         hlist_del_rcu(&l->hash_node);
 322                         htab->count--;
 323                         kfree(l);
 324                 }
 325         }
 326 }
 327
 328 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 329 static void htab_map_free(struct bpf_map *map)
 330 {
 331         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 332
 333         /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
 334          * so the programs (can be more than one that used this map) were
 335          * disconnected from events. Wait for outstanding critical sections in
 336          * these programs to complete
 337          */
 338         synchronize_rcu();
 339
 340         /* some of kfree_rcu() callbacks for elements of this map may not have
 341          * executed. It's ok. Proceed to free residual elements and map itself
 342          */
 343         delete_all_elements(htab);
 344         kvfree(htab->buckets);
 345         kfree(htab);
 346 }
 347
 348 static const struct bpf_map_ops htab_ops = {
 349         .map_alloc = htab_map_alloc,
 350         .map_free = htab_map_free,
 351         .map_get_next_key = htab_map_get_next_key,
 352         .map_lookup_elem = htab_map_lookup_elem,
 353         .map_update_elem = htab_map_update_elem,
 354         .map_delete_elem = htab_map_delete_elem,
 355 };
 356
 357 static struct bpf_map_type_list htab_type __read_mostly = {
 358         .ops = &htab_ops,
 359         .type = BPF_MAP_TYPE_HASH,
 360 };
 361
 362 static int __init register_htab_map(void)
 363 {
 364         bpf_register_map_type(&htab_type);
 365         return 0;
 366 }
 367 late_initcall(register_htab_map);