aboutsummaryrefslogtreecommitdiff
path: root/kernel/bpf/hashtab.c
blob: 34777b3746fadf6407ca9805f33df608be619f21 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 */
#include <linux/bpf.h>
#include <linux/jhash.h>
#include <linux/filter.h>
#include <linux/vmalloc.h>

struct bpf_htab {
	struct bpf_map map;
	struct hlist_head *buckets;
	raw_spinlock_t lock;
	u32 count;	/* number of elements in this hashtable */
	u32 n_buckets;	/* number of hash buckets */
	u32 elem_size;	/* size of each element in bytes */
};

/* each htab element is struct htab_elem + key + value */
struct htab_elem {
	struct hlist_node hash_node;
	struct rcu_head rcu;
	u32 hash;
	char key[0] __aligned(8);
};

/* Called from syscall */
static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
{
	struct bpf_htab *htab;
	int err, i;

	htab = kzalloc(sizeof(*htab), GFP_USER);
	if (!htab)
		return ERR_PTR(-ENOMEM);

	/* mandatory map attributes */
	htab->map.key_size = attr->key_size;
	htab->map.value_size = attr->value_size;
	htab->map.max_entries = attr->max_entries;

	/* check sanity of attributes.
	 * value_size == 0 may be allowed in the future to use map as a set
	 */
	err = -EINVAL;
	if (htab->map.max_entries == 0 || htab->map.key_size == 0 ||
	    htab->map.value_size == 0)
		goto free_htab;

	/* hash table size must be power of 2 */
	htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);

	err = -E2BIG;
	if (htab->map.key_size > MAX_BPF_STACK)
		/* eBPF programs initialize keys on stack, so they cannot be
		 * larger than max stack size
		 */
		goto free_htab;

	if (htab->map.value_size >= (1 << (KMALLOC_SHIFT_MAX - 1)) -
	    MAX_BPF_STACK - sizeof(struct htab_elem))
		/* if value_size is bigger, the user space won't be able to
		 * access the elements via bpf syscall. This check also makes
		 * sure that the elem_size doesn't overflow and it's
		 * kmalloc-able later in htab_map_update_elem()
		 */
		goto free_htab;

	htab->elem_size = sizeof(struct htab_elem) +
			  round_up(htab->map.key_size, 8) +
			  htab->map.value_size;

	/* prevent zero size kmalloc and check for u32 overflow */
	if (htab->n_buckets == 0 ||
	    htab->n_buckets > U32_MAX / sizeof(struct hlist_head))
		goto free_htab;

	if ((u64) htab->n_buckets * sizeof(struct hlist_head) +
	    (u64) htab->elem_size * htab->map.max_entries >=
	    U32_MAX - PAGE_SIZE)
		/* make sure page count doesn't overflow */
		goto free_htab;

	htab->map.pages = round_up(htab->n_buckets * sizeof(struct hlist_head) +
				   htab->elem_size * htab->map.max_entries,
				   PAGE_SIZE) >> PAGE_SHIFT;

	err = -ENOMEM;
	htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
				      GFP_USER | __GFP_NOWARN);

	if (!htab->buckets) {
		htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
		if (!htab->buckets)
			goto free_htab;
	}

	for (i = 0; i < htab->n_buckets; i++)
		INIT_HLIST_HEAD(&htab->buckets[i]);

	raw_spin_lock_init(&htab->lock);
	htab->count = 0;

	return &htab->map;

free_htab:
	kfree(htab);
	return ERR_PTR(err);
}

static inline u32 htab_map_hash(const void *key, u32 key_len)
{
	return jhash(key, key_len, 0);
}

static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
{
	return &htab->buckets[hash & (htab->n_buckets - 1)];
}

static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
					 void *key, u32 key_size)
{
	struct htab_elem *l;

	hlist_for_each_entry_rcu(l, head, hash_node)
		if (l->hash == hash && !memcmp(&l->key, key, key_size))
			return l;

	return NULL;
}

/* Called from syscall or from eBPF program */
static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
{
	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
	struct hlist_head *head;
	struct htab_elem *l;
	u32 hash, key_size;

	/* Must be called with rcu_read_lock. */
	WARN_ON_ONCE(!rcu_read_lock_held());

	key_size = map->key_size;

	hash = htab_map_hash(key, key_size);

	head = select_bucket(htab, hash);

	l = lookup_elem_raw(head, hash, key, key_size);

	if (l)
		return l->key + round_up(map->key_size, 8);

	return NULL;
}

/* Called from syscall */
static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
	struct hlist_head *head;
	struct htab_elem *l, *next_l;
	u32 hash, key_size;
	int i;

	WARN_ON_ONCE(!rcu_read_lock_held());

	key_size = map->key_size;

	hash = htab_map_hash(key, key_size);

	head = select_bucket(htab, hash);

	/* lookup the key */
	l = lookup_elem_raw(head, hash, key, key_size);

	if (!l) {
		i = 0;
		goto find_first_elem;
	}

	/* key was found, get next key in the same bucket */
	next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
				  struct htab_elem, hash_node);

	if (next_l) {
		/* if next elem in this hash list is non-zero, just return it */
		memcpy(next_key, next_l->key, key_size);
		return 0;
	}

	/* no more elements in this hash list, go to the next bucket */
	i = hash & (htab->n_buckets - 1);
	i++;

find_first_elem:
	/* iterate over buckets */
	for (; i < htab->n_buckets; i++) {
		head = select_bucket(htab, i);

		/* pick first element in the bucket */
		next_l = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
					  struct htab_elem, hash_node);
		if (next_l) {
			/* if it's not empty, just return it */
			memcpy(next_key, next_l->key, key_size);
			return 0;
		}
	}

	/* itereated over all buckets and all elements */
	return -ENOENT;
}

/* Called from syscall or from eBPF program */
static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
				u64 map_flags)
{
	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
	struct htab_elem *l_new, *l_old;
	struct hlist_head *head;
	unsigned long flags;
	u32 key_size;
	int ret;

	if (map_flags > BPF_EXIST)
		/* unknown flags */
		return -EINVAL;

	WARN_ON_ONCE(!rcu_read_lock_held());

	/* allocate new element outside of lock */
	l_new = kmalloc(htab->elem_size, GFP_ATOMIC | __GFP_NOWARN);
	if (!l_new)
		return -ENOMEM;

	key_size = map->key_size;

	memcpy(l_new->key, key, key_size);
	memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);

	l_new->hash = htab_map_hash(l_new->key, key_size);

	/* bpf_map_update_elem() can be called in_irq() */
	raw_spin_lock_irqsave(&htab->lock, flags);

	head = select_bucket(htab, l_new->hash);

	l_old = lookup_elem_raw(head, l_new->hash, key, key_size);

	if (!l_old && unlikely(htab->count >= map->max_entries)) {
		/* if elem with this 'key' doesn't exist and we've reached
		 * max_entries limit, fail insertion of new elem
		 */
		ret = -E2BIG;
		goto err;
	}

	if (l_old && map_flags == BPF_NOEXIST) {
		/* elem already exists */
		ret = -EEXIST;
		goto err;
	}

	if (!l_old && map_flags == BPF_EXIST) {
		/* elem doesn't exist, cannot update it */
		ret = -ENOENT;
		goto err;
	}

	/* add new element to the head of the list, so that concurrent
	 * search will find it before old elem
	 */
	hlist_add_head_rcu(&l_new->hash_node, head);
	if (l_old) {
		hlist_del_rcu(&l_old->hash_node);
		kfree_rcu(l_old, rcu);
	} else {
		htab->count++;
	}
	raw_spin_unlock_irqrestore(&htab->lock, flags);

	return 0;
err:
	raw_spin_unlock_irqrestore(&htab->lock, flags);
	kfree(l_new);
	return ret;
}

/* Called from syscall or from eBPF program */
static int htab_map_delete_elem(struct bpf_map *map, void *key)
{
	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
	struct hlist_head *head;
	struct htab_elem *l;
	unsigned long flags;
	u32 hash, key_size;
	int ret = -ENOENT;

	WARN_ON_ONCE(!rcu_read_lock_held());

	key_size = map->key_size;

	hash = htab_map_hash(key, key_size);

	raw_spin_lock_irqsave(&htab->lock, flags);

	head = select_bucket(htab, hash);

	l = lookup_elem_raw(head, hash, key, key_size);

	if (l) {
		hlist_del_rcu(&l->hash_node);
		htab->count--;
		kfree_rcu(l, rcu);
		ret = 0;
	}

	raw_spin_unlock_irqrestore(&htab->lock, flags);
	return ret;
}

static void delete_all_elements(struct bpf_htab *htab)
{
	int i;

	for (i = 0; i < htab->n_buckets; i++) {
		struct hlist_head *head = select_bucket(htab, i);
		struct hlist_node *n;
		struct htab_elem *l;

		hlist_for_each_entry_safe(l, n, head, hash_node) {
			hlist_del_rcu(&l->hash_node);
			htab->count--;
			kfree(l);
		}
	}
}

/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void htab_map_free(struct bpf_map *map)
{
	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

	/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
	 * so the programs (can be more than one that used this map) were
	 * disconnected from events. Wait for outstanding critical sections in
	 * these programs to complete
	 */
	synchronize_rcu();

	/* some of kfree_rcu() callbacks for elements of this map may not have
	 * executed. It's ok. Proceed to free residual elements and map itself
	 */
	delete_all_elements(htab);
	kvfree(htab->buckets);
	kfree(htab);
}

static const struct bpf_map_ops htab_ops = {
	.map_alloc = htab_map_alloc,
	.map_free = htab_map_free,
	.map_get_next_key = htab_map_get_next_key,
	.map_lookup_elem = htab_map_lookup_elem,
	.map_update_elem = htab_map_update_elem,
	.map_delete_elem = htab_map_delete_elem,
};

static struct bpf_map_type_list htab_type __read_mostly = {
	.ops = &htab_ops,
	.type = BPF_MAP_TYPE_HASH,
};

static int __init register_htab_map(void)
{
	bpf_register_map_type(&htab_type);
	return 0;
}
late_initcall(register_htab_map);