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         raw_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         raw_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
  92         htab->map.pages = round_up(htab->n_buckets * sizeof(struct hlist_head) +
  93                                    htab->elem_size * htab->map.max_entries,
  94                                    PAGE_SIZE) >> PAGE_SHIFT;
  95         return &htab->map;
  96
  97 free_htab:
  98         kfree(htab);
  99         return ERR_PTR(err);
 100 }
 101
 102 static inline u32 htab_map_hash(const void *key, u32 key_len)
 103 {
 104         return jhash(key, key_len, 0);
 105 }
 106
 107 static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
 108 {
 109         return &htab->buckets[hash & (htab->n_buckets - 1)];
 110 }
 111
 112 static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
 113                                          void *key, u32 key_size)
 114 {
 115         struct htab_elem *l;
 116
 117         hlist_for_each_entry_rcu(l, head, hash_node)
 118                 if (l->hash == hash && !memcmp(&l->key, key, key_size))
 119                         return l;
 120
 121         return NULL;
 122 }
 123
 124 /* Called from syscall or from eBPF program */
 125 static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
 126 {
 127         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 128         struct hlist_head *head;
 129         struct htab_elem *l;
 130         u32 hash, key_size;
 131
 132         /* Must be called with rcu_read_lock. */
 133         WARN_ON_ONCE(!rcu_read_lock_held());
 134
 135         key_size = map->key_size;
 136
 137         hash = htab_map_hash(key, key_size);
 138
 139         head = select_bucket(htab, hash);
 140
 141         l = lookup_elem_raw(head, hash, key, key_size);
 142
 143         if (l)
 144                 return l->key + round_up(map->key_size, 8);
 145
 146         return NULL;
 147 }
 148
 149 /* Called from syscall */
 150 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
 151 {
 152         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 153         struct hlist_head *head;
 154         struct htab_elem *l, *next_l;
 155         u32 hash, key_size;
 156         int i;
 157
 158         WARN_ON_ONCE(!rcu_read_lock_held());
 159
 160         key_size = map->key_size;
 161
 162         hash = htab_map_hash(key, key_size);
 163
 164         head = select_bucket(htab, hash);
 165
 166         /* lookup the key */
 167         l = lookup_elem_raw(head, hash, key, key_size);
 168
 169         if (!l) {
 170                 i = 0;
 171                 goto find_first_elem;
 172         }
 173
 174         /* key was found, get next key in the same bucket */
 175         next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
 176                                   struct htab_elem, hash_node);
 177
 178         if (next_l) {
 179                 /* if next elem in this hash list is non-zero, just return it */
 180                 memcpy(next_key, next_l->key, key_size);
 181                 return 0;
 182         }
 183
 184         /* no more elements in this hash list, go to the next bucket */
 185         i = hash & (htab->n_buckets - 1);
 186         i++;
 187
 188 find_first_elem:
 189         /* iterate over buckets */
 190         for (; i < htab->n_buckets; i++) {
 191                 head = select_bucket(htab, i);
 192
 193                 /* pick first element in the bucket */
 194                 next_l = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
 195                                           struct htab_elem, hash_node);
 196                 if (next_l) {
 197                         /* if it's not empty, just return it */
 198                         memcpy(next_key, next_l->key, key_size);
 199                         return 0;
 200                 }
 201         }
 202
 203         /* itereated over all buckets and all elements */
 204         return -ENOENT;
 205 }
 206
 207 /* Called from syscall or from eBPF program */
 208 static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 209                                 u64 map_flags)
 210 {
 211         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 212         struct htab_elem *l_new, *l_old;
 213         struct hlist_head *head;
 214         unsigned long flags;
 215         u32 key_size;
 216         int ret;
 217
 218         if (map_flags > BPF_EXIST)
 219                 /* unknown flags */
 220                 return -EINVAL;
 221
 222         WARN_ON_ONCE(!rcu_read_lock_held());
 223
 224         /* allocate new element outside of lock */
 225         l_new = kmalloc(htab->elem_size, GFP_ATOMIC);
 226         if (!l_new)
 227                 return -ENOMEM;
 228
 229         key_size = map->key_size;
 230
 231         memcpy(l_new->key, key, key_size);
 232         memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);
 233
 234         l_new->hash = htab_map_hash(l_new->key, key_size);
 235
 236         /* bpf_map_update_elem() can be called in_irq() */
 237         raw_spin_lock_irqsave(&htab->lock, flags);
 238
 239         head = select_bucket(htab, l_new->hash);
 240
 241         l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
 242
 243         if (!l_old && unlikely(htab->count >= map->max_entries)) {
 244                 /* if elem with this 'key' doesn't exist and we've reached
 245                  * max_entries limit, fail insertion of new elem
 246                  */
 247                 ret = -E2BIG;
 248                 goto err;
 249         }
 250
 251         if (l_old && map_flags == BPF_NOEXIST) {
 252                 /* elem already exists */
 253                 ret = -EEXIST;
 254                 goto err;
 255         }
 256
 257         if (!l_old && map_flags == BPF_EXIST) {
 258                 /* elem doesn't exist, cannot update it */
 259                 ret = -ENOENT;
 260                 goto err;
 261         }
 262
 263         /* add new element to the head of the list, so that concurrent
 264          * search will find it before old elem
 265          */
 266         hlist_add_head_rcu(&l_new->hash_node, head);
 267         if (l_old) {
 268                 hlist_del_rcu(&l_old->hash_node);
 269                 kfree_rcu(l_old, rcu);
 270         } else {
 271                 htab->count++;
 272         }
 273         raw_spin_unlock_irqrestore(&htab->lock, flags);
 274
 275         return 0;
 276 err:
 277         raw_spin_unlock_irqrestore(&htab->lock, flags);
 278         kfree(l_new);
 279         return ret;
 280 }
 281
 282 /* Called from syscall or from eBPF program */
 283 static int htab_map_delete_elem(struct bpf_map *map, void *key)
 284 {
 285         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 286         struct hlist_head *head;
 287         struct htab_elem *l;
 288         unsigned long flags;
 289         u32 hash, key_size;
 290         int ret = -ENOENT;
 291
 292         WARN_ON_ONCE(!rcu_read_lock_held());
 293
 294         key_size = map->key_size;
 295
 296         hash = htab_map_hash(key, key_size);
 297
 298         raw_spin_lock_irqsave(&htab->lock, flags);
 299
 300         head = select_bucket(htab, hash);
 301
 302         l = lookup_elem_raw(head, hash, key, key_size);
 303
 304         if (l) {
 305                 hlist_del_rcu(&l->hash_node);
 306                 htab->count--;
 307                 kfree_rcu(l, rcu);
 308                 ret = 0;
 309         }
 310
 311         raw_spin_unlock_irqrestore(&htab->lock, flags);
 312         return ret;
 313 }
 314
 315 static void delete_all_elements(struct bpf_htab *htab)
 316 {
 317         int i;
 318
 319         for (i = 0; i < htab->n_buckets; i++) {
 320                 struct hlist_head *head = select_bucket(htab, i);
 321                 struct hlist_node *n;
 322                 struct htab_elem *l;
 323
 324                 hlist_for_each_entry_safe(l, n, head, hash_node) {
 325                         hlist_del_rcu(&l->hash_node);
 326                         htab->count--;
 327                         kfree(l);
 328                 }
 329         }
 330 }
 331
 332 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 333 static void htab_map_free(struct bpf_map *map)
 334 {
 335         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
 336
 337         /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
 338          * so the programs (can be more than one that used this map) were
 339          * disconnected from events. Wait for outstanding critical sections in
 340          * these programs to complete
 341          */
 342         synchronize_rcu();
 343
 344         /* some of kfree_rcu() callbacks for elements of this map may not have
 345          * executed. It's ok. Proceed to free residual elements and map itself
 346          */
 347         delete_all_elements(htab);
 348         kvfree(htab->buckets);
 349         kfree(htab);
 350 }
 351
 352 static const struct bpf_map_ops htab_ops = {
 353         .map_alloc = htab_map_alloc,
 354         .map_free = htab_map_free,
 355         .map_get_next_key = htab_map_get_next_key,
 356         .map_lookup_elem = htab_map_lookup_elem,
 357         .map_update_elem = htab_map_update_elem,
 358         .map_delete_elem = htab_map_delete_elem,
 359 };
 360
 361 static struct bpf_map_type_list htab_type __read_mostly = {
 362         .ops = &htab_ops,
 363         .type = BPF_MAP_TYPE_HASH,
 364 };
 365
 366 static int __init register_htab_map(void)
 367 {
 368         bpf_register_map_type(&htab_type);
 369         return 0;
 370 }
 371 late_initcall(register_htab_map);