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b95a5c4d DM |
1 | /* |
2 | * Longest prefix match list implementation | |
3 | * | |
4 | * Copyright (c) 2016,2017 Daniel Mack | |
5 | * Copyright (c) 2016 David Herrmann | |
6 | * | |
7 | * This file is subject to the terms and conditions of version 2 of the GNU | |
8 | * General Public License. See the file COPYING in the main directory of the | |
9 | * Linux distribution for more details. | |
10 | */ | |
11 | ||
12 | #include <linux/bpf.h> | |
13 | #include <linux/err.h> | |
14 | #include <linux/slab.h> | |
15 | #include <linux/spinlock.h> | |
16 | #include <linux/vmalloc.h> | |
17 | #include <net/ipv6.h> | |
18 | ||
19 | /* Intermediate node */ | |
20 | #define LPM_TREE_NODE_FLAG_IM BIT(0) | |
21 | ||
22 | struct lpm_trie_node; | |
23 | ||
24 | struct lpm_trie_node { | |
25 | struct rcu_head rcu; | |
26 | struct lpm_trie_node __rcu *child[2]; | |
27 | u32 prefixlen; | |
28 | u32 flags; | |
29 | u8 data[0]; | |
30 | }; | |
31 | ||
32 | struct lpm_trie { | |
33 | struct bpf_map map; | |
34 | struct lpm_trie_node __rcu *root; | |
35 | size_t n_entries; | |
36 | size_t max_prefixlen; | |
37 | size_t data_size; | |
38 | raw_spinlock_t lock; | |
39 | }; | |
40 | ||
41 | /* This trie implements a longest prefix match algorithm that can be used to | |
42 | * match IP addresses to a stored set of ranges. | |
43 | * | |
44 | * Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is | |
45 | * interpreted as big endian, so data[0] stores the most significant byte. | |
46 | * | |
47 | * Match ranges are internally stored in instances of struct lpm_trie_node | |
48 | * which each contain their prefix length as well as two pointers that may | |
49 | * lead to more nodes containing more specific matches. Each node also stores | |
50 | * a value that is defined by and returned to userspace via the update_elem | |
51 | * and lookup functions. | |
52 | * | |
53 | * For instance, let's start with a trie that was created with a prefix length | |
54 | * of 32, so it can be used for IPv4 addresses, and one single element that | |
55 | * matches 192.168.0.0/16. The data array would hence contain | |
56 | * [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will | |
57 | * stick to IP-address notation for readability though. | |
58 | * | |
59 | * As the trie is empty initially, the new node (1) will be places as root | |
60 | * node, denoted as (R) in the example below. As there are no other node, both | |
61 | * child pointers are %NULL. | |
62 | * | |
63 | * +----------------+ | |
64 | * | (1) (R) | | |
65 | * | 192.168.0.0/16 | | |
66 | * | value: 1 | | |
67 | * | [0] [1] | | |
68 | * +----------------+ | |
69 | * | |
70 | * Next, let's add a new node (2) matching 192.168.0.0/24. As there is already | |
71 | * a node with the same data and a smaller prefix (ie, a less specific one), | |
72 | * node (2) will become a child of (1). In child index depends on the next bit | |
73 | * that is outside of what (1) matches, and that bit is 0, so (2) will be | |
74 | * child[0] of (1): | |
75 | * | |
76 | * +----------------+ | |
77 | * | (1) (R) | | |
78 | * | 192.168.0.0/16 | | |
79 | * | value: 1 | | |
80 | * | [0] [1] | | |
81 | * +----------------+ | |
82 | * | | |
83 | * +----------------+ | |
84 | * | (2) | | |
85 | * | 192.168.0.0/24 | | |
86 | * | value: 2 | | |
87 | * | [0] [1] | | |
88 | * +----------------+ | |
89 | * | |
90 | * The child[1] slot of (1) could be filled with another node which has bit #17 | |
91 | * (the next bit after the ones that (1) matches on) set to 1. For instance, | |
92 | * 192.168.128.0/24: | |
93 | * | |
94 | * +----------------+ | |
95 | * | (1) (R) | | |
96 | * | 192.168.0.0/16 | | |
97 | * | value: 1 | | |
98 | * | [0] [1] | | |
99 | * +----------------+ | |
100 | * | | | |
101 | * +----------------+ +------------------+ | |
102 | * | (2) | | (3) | | |
103 | * | 192.168.0.0/24 | | 192.168.128.0/24 | | |
104 | * | value: 2 | | value: 3 | | |
105 | * | [0] [1] | | [0] [1] | | |
106 | * +----------------+ +------------------+ | |
107 | * | |
108 | * Let's add another node (4) to the game for 192.168.1.0/24. In order to place | |
109 | * it, node (1) is looked at first, and because (4) of the semantics laid out | |
110 | * above (bit #17 is 0), it would normally be attached to (1) as child[0]. | |
111 | * However, that slot is already allocated, so a new node is needed in between. | |
112 | * That node does not have a value attached to it and it will never be | |
113 | * returned to users as result of a lookup. It is only there to differentiate | |
114 | * the traversal further. It will get a prefix as wide as necessary to | |
115 | * distinguish its two children: | |
116 | * | |
117 | * +----------------+ | |
118 | * | (1) (R) | | |
119 | * | 192.168.0.0/16 | | |
120 | * | value: 1 | | |
121 | * | [0] [1] | | |
122 | * +----------------+ | |
123 | * | | | |
124 | * +----------------+ +------------------+ | |
125 | * | (4) (I) | | (3) | | |
126 | * | 192.168.0.0/23 | | 192.168.128.0/24 | | |
127 | * | value: --- | | value: 3 | | |
128 | * | [0] [1] | | [0] [1] | | |
129 | * +----------------+ +------------------+ | |
130 | * | | | |
131 | * +----------------+ +----------------+ | |
132 | * | (2) | | (5) | | |
133 | * | 192.168.0.0/24 | | 192.168.1.0/24 | | |
134 | * | value: 2 | | value: 5 | | |
135 | * | [0] [1] | | [0] [1] | | |
136 | * +----------------+ +----------------+ | |
137 | * | |
138 | * 192.168.1.1/32 would be a child of (5) etc. | |
139 | * | |
140 | * An intermediate node will be turned into a 'real' node on demand. In the | |
141 | * example above, (4) would be re-used if 192.168.0.0/23 is added to the trie. | |
142 | * | |
143 | * A fully populated trie would have a height of 32 nodes, as the trie was | |
144 | * created with a prefix length of 32. | |
145 | * | |
146 | * The lookup starts at the root node. If the current node matches and if there | |
147 | * is a child that can be used to become more specific, the trie is traversed | |
148 | * downwards. The last node in the traversal that is a non-intermediate one is | |
149 | * returned. | |
150 | */ | |
151 | ||
152 | static inline int extract_bit(const u8 *data, size_t index) | |
153 | { | |
154 | return !!(data[index / 8] & (1 << (7 - (index % 8)))); | |
155 | } | |
156 | ||
157 | /** | |
158 | * longest_prefix_match() - determine the longest prefix | |
159 | * @trie: The trie to get internal sizes from | |
160 | * @node: The node to operate on | |
161 | * @key: The key to compare to @node | |
162 | * | |
163 | * Determine the longest prefix of @node that matches the bits in @key. | |
164 | */ | |
165 | static size_t longest_prefix_match(const struct lpm_trie *trie, | |
166 | const struct lpm_trie_node *node, | |
167 | const struct bpf_lpm_trie_key *key) | |
168 | { | |
169 | size_t prefixlen = 0; | |
170 | size_t i; | |
171 | ||
172 | for (i = 0; i < trie->data_size; i++) { | |
173 | size_t b; | |
174 | ||
175 | b = 8 - fls(node->data[i] ^ key->data[i]); | |
176 | prefixlen += b; | |
177 | ||
178 | if (prefixlen >= node->prefixlen || prefixlen >= key->prefixlen) | |
179 | return min(node->prefixlen, key->prefixlen); | |
180 | ||
181 | if (b < 8) | |
182 | break; | |
183 | } | |
184 | ||
185 | return prefixlen; | |
186 | } | |
187 | ||
188 | /* Called from syscall or from eBPF program */ | |
189 | static void *trie_lookup_elem(struct bpf_map *map, void *_key) | |
190 | { | |
191 | struct lpm_trie *trie = container_of(map, struct lpm_trie, map); | |
192 | struct lpm_trie_node *node, *found = NULL; | |
193 | struct bpf_lpm_trie_key *key = _key; | |
194 | ||
195 | /* Start walking the trie from the root node ... */ | |
196 | ||
197 | for (node = rcu_dereference(trie->root); node;) { | |
198 | unsigned int next_bit; | |
199 | size_t matchlen; | |
200 | ||
201 | /* Determine the longest prefix of @node that matches @key. | |
202 | * If it's the maximum possible prefix for this trie, we have | |
203 | * an exact match and can return it directly. | |
204 | */ | |
205 | matchlen = longest_prefix_match(trie, node, key); | |
206 | if (matchlen == trie->max_prefixlen) { | |
207 | found = node; | |
208 | break; | |
209 | } | |
210 | ||
211 | /* If the number of bits that match is smaller than the prefix | |
212 | * length of @node, bail out and return the node we have seen | |
213 | * last in the traversal (ie, the parent). | |
214 | */ | |
215 | if (matchlen < node->prefixlen) | |
216 | break; | |
217 | ||
218 | /* Consider this node as return candidate unless it is an | |
219 | * artificially added intermediate one. | |
220 | */ | |
221 | if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) | |
222 | found = node; | |
223 | ||
224 | /* If the node match is fully satisfied, let's see if we can | |
225 | * become more specific. Determine the next bit in the key and | |
226 | * traverse down. | |
227 | */ | |
228 | next_bit = extract_bit(key->data, node->prefixlen); | |
229 | node = rcu_dereference(node->child[next_bit]); | |
230 | } | |
231 | ||
232 | if (!found) | |
233 | return NULL; | |
234 | ||
235 | return found->data + trie->data_size; | |
236 | } | |
237 | ||
238 | static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie, | |
239 | const void *value) | |
240 | { | |
241 | struct lpm_trie_node *node; | |
242 | size_t size = sizeof(struct lpm_trie_node) + trie->data_size; | |
243 | ||
244 | if (value) | |
245 | size += trie->map.value_size; | |
246 | ||
247 | node = kmalloc(size, GFP_ATOMIC | __GFP_NOWARN); | |
248 | if (!node) | |
249 | return NULL; | |
250 | ||
251 | node->flags = 0; | |
252 | ||
253 | if (value) | |
254 | memcpy(node->data + trie->data_size, value, | |
255 | trie->map.value_size); | |
256 | ||
257 | return node; | |
258 | } | |
259 | ||
260 | /* Called from syscall or from eBPF program */ | |
261 | static int trie_update_elem(struct bpf_map *map, | |
262 | void *_key, void *value, u64 flags) | |
263 | { | |
264 | struct lpm_trie *trie = container_of(map, struct lpm_trie, map); | |
d140199a | 265 | struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL; |
b95a5c4d DM |
266 | struct lpm_trie_node __rcu **slot; |
267 | struct bpf_lpm_trie_key *key = _key; | |
268 | unsigned long irq_flags; | |
269 | unsigned int next_bit; | |
270 | size_t matchlen = 0; | |
271 | int ret = 0; | |
272 | ||
273 | if (unlikely(flags > BPF_EXIST)) | |
274 | return -EINVAL; | |
275 | ||
276 | if (key->prefixlen > trie->max_prefixlen) | |
277 | return -EINVAL; | |
278 | ||
279 | raw_spin_lock_irqsave(&trie->lock, irq_flags); | |
280 | ||
281 | /* Allocate and fill a new node */ | |
282 | ||
283 | if (trie->n_entries == trie->map.max_entries) { | |
284 | ret = -ENOSPC; | |
285 | goto out; | |
286 | } | |
287 | ||
288 | new_node = lpm_trie_node_alloc(trie, value); | |
289 | if (!new_node) { | |
290 | ret = -ENOMEM; | |
291 | goto out; | |
292 | } | |
293 | ||
294 | trie->n_entries++; | |
295 | ||
296 | new_node->prefixlen = key->prefixlen; | |
297 | RCU_INIT_POINTER(new_node->child[0], NULL); | |
298 | RCU_INIT_POINTER(new_node->child[1], NULL); | |
299 | memcpy(new_node->data, key->data, trie->data_size); | |
300 | ||
301 | /* Now find a slot to attach the new node. To do that, walk the tree | |
302 | * from the root and match as many bits as possible for each node until | |
303 | * we either find an empty slot or a slot that needs to be replaced by | |
304 | * an intermediate node. | |
305 | */ | |
306 | slot = &trie->root; | |
307 | ||
308 | while ((node = rcu_dereference_protected(*slot, | |
309 | lockdep_is_held(&trie->lock)))) { | |
310 | matchlen = longest_prefix_match(trie, node, key); | |
311 | ||
312 | if (node->prefixlen != matchlen || | |
313 | node->prefixlen == key->prefixlen || | |
314 | node->prefixlen == trie->max_prefixlen) | |
315 | break; | |
316 | ||
317 | next_bit = extract_bit(key->data, node->prefixlen); | |
318 | slot = &node->child[next_bit]; | |
319 | } | |
320 | ||
321 | /* If the slot is empty (a free child pointer or an empty root), | |
322 | * simply assign the @new_node to that slot and be done. | |
323 | */ | |
324 | if (!node) { | |
325 | rcu_assign_pointer(*slot, new_node); | |
326 | goto out; | |
327 | } | |
328 | ||
329 | /* If the slot we picked already exists, replace it with @new_node | |
330 | * which already has the correct data array set. | |
331 | */ | |
332 | if (node->prefixlen == matchlen) { | |
333 | new_node->child[0] = node->child[0]; | |
334 | new_node->child[1] = node->child[1]; | |
335 | ||
336 | if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) | |
337 | trie->n_entries--; | |
338 | ||
339 | rcu_assign_pointer(*slot, new_node); | |
340 | kfree_rcu(node, rcu); | |
341 | ||
342 | goto out; | |
343 | } | |
344 | ||
345 | /* If the new node matches the prefix completely, it must be inserted | |
346 | * as an ancestor. Simply insert it between @node and *@slot. | |
347 | */ | |
348 | if (matchlen == key->prefixlen) { | |
349 | next_bit = extract_bit(node->data, matchlen); | |
350 | rcu_assign_pointer(new_node->child[next_bit], node); | |
351 | rcu_assign_pointer(*slot, new_node); | |
352 | goto out; | |
353 | } | |
354 | ||
355 | im_node = lpm_trie_node_alloc(trie, NULL); | |
356 | if (!im_node) { | |
357 | ret = -ENOMEM; | |
358 | goto out; | |
359 | } | |
360 | ||
361 | im_node->prefixlen = matchlen; | |
362 | im_node->flags |= LPM_TREE_NODE_FLAG_IM; | |
363 | memcpy(im_node->data, node->data, trie->data_size); | |
364 | ||
365 | /* Now determine which child to install in which slot */ | |
366 | if (extract_bit(key->data, matchlen)) { | |
367 | rcu_assign_pointer(im_node->child[0], node); | |
368 | rcu_assign_pointer(im_node->child[1], new_node); | |
369 | } else { | |
370 | rcu_assign_pointer(im_node->child[0], new_node); | |
371 | rcu_assign_pointer(im_node->child[1], node); | |
372 | } | |
373 | ||
374 | /* Finally, assign the intermediate node to the determined spot */ | |
375 | rcu_assign_pointer(*slot, im_node); | |
376 | ||
377 | out: | |
378 | if (ret) { | |
379 | if (new_node) | |
380 | trie->n_entries--; | |
381 | ||
382 | kfree(new_node); | |
383 | kfree(im_node); | |
384 | } | |
385 | ||
386 | raw_spin_unlock_irqrestore(&trie->lock, irq_flags); | |
387 | ||
388 | return ret; | |
389 | } | |
390 | ||
391 | static int trie_delete_elem(struct bpf_map *map, void *key) | |
392 | { | |
393 | /* TODO */ | |
394 | return -ENOSYS; | |
395 | } | |
396 | ||
397 | static struct bpf_map *trie_alloc(union bpf_attr *attr) | |
398 | { | |
399 | size_t cost, cost_per_node; | |
400 | struct lpm_trie *trie; | |
401 | int ret; | |
402 | ||
403 | if (!capable(CAP_SYS_ADMIN)) | |
404 | return ERR_PTR(-EPERM); | |
405 | ||
406 | /* check sanity of attributes */ | |
407 | if (attr->max_entries == 0 || | |
408 | attr->map_flags != BPF_F_NO_PREALLOC || | |
409 | attr->key_size < sizeof(struct bpf_lpm_trie_key) + 1 || | |
410 | attr->key_size > sizeof(struct bpf_lpm_trie_key) + 256 || | |
411 | attr->value_size == 0) | |
412 | return ERR_PTR(-EINVAL); | |
413 | ||
414 | trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN); | |
415 | if (!trie) | |
416 | return ERR_PTR(-ENOMEM); | |
417 | ||
418 | /* copy mandatory map attributes */ | |
419 | trie->map.map_type = attr->map_type; | |
420 | trie->map.key_size = attr->key_size; | |
421 | trie->map.value_size = attr->value_size; | |
422 | trie->map.max_entries = attr->max_entries; | |
423 | trie->data_size = attr->key_size - | |
424 | offsetof(struct bpf_lpm_trie_key, data); | |
425 | trie->max_prefixlen = trie->data_size * 8; | |
426 | ||
427 | cost_per_node = sizeof(struct lpm_trie_node) + | |
428 | attr->value_size + trie->data_size; | |
429 | cost = sizeof(*trie) + attr->max_entries * cost_per_node; | |
430 | trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT; | |
431 | ||
432 | ret = bpf_map_precharge_memlock(trie->map.pages); | |
433 | if (ret) { | |
434 | kfree(trie); | |
435 | return ERR_PTR(ret); | |
436 | } | |
437 | ||
438 | raw_spin_lock_init(&trie->lock); | |
439 | ||
440 | return &trie->map; | |
441 | } | |
442 | ||
443 | static void trie_free(struct bpf_map *map) | |
444 | { | |
445 | struct lpm_trie *trie = container_of(map, struct lpm_trie, map); | |
446 | struct lpm_trie_node __rcu **slot; | |
447 | struct lpm_trie_node *node; | |
448 | ||
449 | raw_spin_lock(&trie->lock); | |
450 | ||
451 | /* Always start at the root and walk down to a node that has no | |
452 | * children. Then free that node, nullify its reference in the parent | |
453 | * and start over. | |
454 | */ | |
455 | ||
456 | for (;;) { | |
457 | slot = &trie->root; | |
458 | ||
459 | for (;;) { | |
460 | node = rcu_dereference_protected(*slot, | |
461 | lockdep_is_held(&trie->lock)); | |
462 | if (!node) | |
463 | goto unlock; | |
464 | ||
465 | if (rcu_access_pointer(node->child[0])) { | |
466 | slot = &node->child[0]; | |
467 | continue; | |
468 | } | |
469 | ||
470 | if (rcu_access_pointer(node->child[1])) { | |
471 | slot = &node->child[1]; | |
472 | continue; | |
473 | } | |
474 | ||
475 | kfree(node); | |
476 | RCU_INIT_POINTER(*slot, NULL); | |
477 | break; | |
478 | } | |
479 | } | |
480 | ||
481 | unlock: | |
482 | raw_spin_unlock(&trie->lock); | |
483 | } | |
484 | ||
485 | static const struct bpf_map_ops trie_ops = { | |
486 | .map_alloc = trie_alloc, | |
487 | .map_free = trie_free, | |
488 | .map_lookup_elem = trie_lookup_elem, | |
489 | .map_update_elem = trie_update_elem, | |
490 | .map_delete_elem = trie_delete_elem, | |
491 | }; | |
492 | ||
493 | static struct bpf_map_type_list trie_type __read_mostly = { | |
494 | .ops = &trie_ops, | |
495 | .type = BPF_MAP_TYPE_LPM_TRIE, | |
496 | }; | |
497 | ||
498 | static int __init register_trie_map(void) | |
499 | { | |
500 | bpf_register_map_type(&trie_type); | |
501 | return 0; | |
502 | } | |
503 | late_initcall(register_trie_map); |