diff options
Diffstat (limited to 'kernel/bpf/lpm_trie.c')
| -rw-r--r-- | kernel/bpf/lpm_trie.c | 714 |
1 files changed, 714 insertions, 0 deletions
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c new file mode 100644 index 000000000..1a8b208f6 --- /dev/null +++ b/kernel/bpf/lpm_trie.c @@ -0,0 +1,714 @@ +/* + * Longest prefix match list implementation + * + * Copyright (c) 2016,2017 Daniel Mack + * Copyright (c) 2016 David Herrmann + * + * This file is subject to the terms and conditions of version 2 of the GNU + * General Public License. See the file COPYING in the main directory of the + * Linux distribution for more details. + */ + +#include <linux/bpf.h> +#include <linux/btf.h> +#include <linux/err.h> +#include <linux/slab.h> +#include <linux/spinlock.h> +#include <linux/vmalloc.h> +#include <net/ipv6.h> +#include <uapi/linux/btf.h> + +/* Intermediate node */ +#define LPM_TREE_NODE_FLAG_IM BIT(0) + +struct lpm_trie_node; + +struct lpm_trie_node { + struct rcu_head rcu; + struct lpm_trie_node __rcu *child[2]; + u32 prefixlen; + u32 flags; + u8 data[0]; +}; + +struct lpm_trie { + struct bpf_map map; + struct lpm_trie_node __rcu *root; + size_t n_entries; + size_t max_prefixlen; + size_t data_size; + raw_spinlock_t lock; +}; + +/* This trie implements a longest prefix match algorithm that can be used to + * match IP addresses to a stored set of ranges. + * + * Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is + * interpreted as big endian, so data[0] stores the most significant byte. + * + * Match ranges are internally stored in instances of struct lpm_trie_node + * which each contain their prefix length as well as two pointers that may + * lead to more nodes containing more specific matches. Each node also stores + * a value that is defined by and returned to userspace via the update_elem + * and lookup functions. + * + * For instance, let's start with a trie that was created with a prefix length + * of 32, so it can be used for IPv4 addresses, and one single element that + * matches 192.168.0.0/16. The data array would hence contain + * [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will + * stick to IP-address notation for readability though. + * + * As the trie is empty initially, the new node (1) will be places as root + * node, denoted as (R) in the example below. As there are no other node, both + * child pointers are %NULL. + * + * +----------------+ + * | (1) (R) | + * | 192.168.0.0/16 | + * | value: 1 | + * | [0] [1] | + * +----------------+ + * + * Next, let's add a new node (2) matching 192.168.0.0/24. As there is already + * a node with the same data and a smaller prefix (ie, a less specific one), + * node (2) will become a child of (1). In child index depends on the next bit + * that is outside of what (1) matches, and that bit is 0, so (2) will be + * child[0] of (1): + * + * +----------------+ + * | (1) (R) | + * | 192.168.0.0/16 | + * | value: 1 | + * | [0] [1] | + * +----------------+ + * | + * +----------------+ + * | (2) | + * | 192.168.0.0/24 | + * | value: 2 | + * | [0] [1] | + * +----------------+ + * + * The child[1] slot of (1) could be filled with another node which has bit #17 + * (the next bit after the ones that (1) matches on) set to 1. For instance, + * 192.168.128.0/24: + * + * +----------------+ + * | (1) (R) | + * | 192.168.0.0/16 | + * | value: 1 | + * | [0] [1] | + * +----------------+ + * | | + * +----------------+ +------------------+ + * | (2) | | (3) | + * | 192.168.0.0/24 | | 192.168.128.0/24 | + * | value: 2 | | value: 3 | + * | [0] [1] | | [0] [1] | + * +----------------+ +------------------+ + * + * Let's add another node (4) to the game for 192.168.1.0/24. In order to place + * it, node (1) is looked at first, and because (4) of the semantics laid out + * above (bit #17 is 0), it would normally be attached to (1) as child[0]. + * However, that slot is already allocated, so a new node is needed in between. + * That node does not have a value attached to it and it will never be + * returned to users as result of a lookup. It is only there to differentiate + * the traversal further. It will get a prefix as wide as necessary to + * distinguish its two children: + * + * +----------------+ + * | (1) (R) | + * | 192.168.0.0/16 | + * | value: 1 | + * | [0] [1] | + * +----------------+ + * | | + * +----------------+ +------------------+ + * | (4) (I) | | (3) | + * | 192.168.0.0/23 | | 192.168.128.0/24 | + * | value: --- | | value: 3 | + * | [0] [1] | | [0] [1] | + * +----------------+ +------------------+ + * | | + * +----------------+ +----------------+ + * | (2) | | (5) | + * | 192.168.0.0/24 | | 192.168.1.0/24 | + * | value: 2 | | value: 5 | + * | [0] [1] | | [0] [1] | + * +----------------+ +----------------+ + * + * 192.168.1.1/32 would be a child of (5) etc. + * + * An intermediate node will be turned into a 'real' node on demand. In the + * example above, (4) would be re-used if 192.168.0.0/23 is added to the trie. + * + * A fully populated trie would have a height of 32 nodes, as the trie was + * created with a prefix length of 32. + * + * The lookup starts at the root node. If the current node matches and if there + * is a child that can be used to become more specific, the trie is traversed + * downwards. The last node in the traversal that is a non-intermediate one is + * returned. + */ + +static inline int extract_bit(const u8 *data, size_t index) +{ + return !!(data[index / 8] & (1 << (7 - (index % 8)))); +} + +/** + * longest_prefix_match() - determine the longest prefix + * @trie: The trie to get internal sizes from + * @node: The node to operate on + * @key: The key to compare to @node + * + * Determine the longest prefix of @node that matches the bits in @key. + */ +static size_t longest_prefix_match(const struct lpm_trie *trie, + const struct lpm_trie_node *node, + const struct bpf_lpm_trie_key *key) +{ + size_t prefixlen = 0; + size_t i; + + for (i = 0; i < trie->data_size; i++) { + size_t b; + + b = 8 - fls(node->data[i] ^ key->data[i]); + prefixlen += b; + + if (prefixlen >= node->prefixlen || prefixlen >= key->prefixlen) + return min(node->prefixlen, key->prefixlen); + + if (b < 8) + break; + } + + return prefixlen; +} + +/* Called from syscall or from eBPF program */ +static void *trie_lookup_elem(struct bpf_map *map, void *_key) +{ + struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct lpm_trie_node *node, *found = NULL; + struct bpf_lpm_trie_key *key = _key; + + /* Start walking the trie from the root node ... */ + + for (node = rcu_dereference(trie->root); node;) { + unsigned int next_bit; + size_t matchlen; + + /* Determine the longest prefix of @node that matches @key. + * If it's the maximum possible prefix for this trie, we have + * an exact match and can return it directly. + */ + matchlen = longest_prefix_match(trie, node, key); + if (matchlen == trie->max_prefixlen) { + found = node; + break; + } + + /* If the number of bits that match is smaller than the prefix + * length of @node, bail out and return the node we have seen + * last in the traversal (ie, the parent). + */ + if (matchlen < node->prefixlen) + break; + + /* Consider this node as return candidate unless it is an + * artificially added intermediate one. + */ + if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) + found = node; + + /* If the node match is fully satisfied, let's see if we can + * become more specific. Determine the next bit in the key and + * traverse down. + */ + next_bit = extract_bit(key->data, node->prefixlen); + node = rcu_dereference(node->child[next_bit]); + } + + if (!found) + return NULL; + + return found->data + trie->data_size; +} + +static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie, + const void *value) +{ + struct lpm_trie_node *node; + size_t size = sizeof(struct lpm_trie_node) + trie->data_size; + + if (value) + size += trie->map.value_size; + + node = kmalloc_node(size, GFP_ATOMIC | __GFP_NOWARN, + trie->map.numa_node); + if (!node) + return NULL; + + node->flags = 0; + + if (value) + memcpy(node->data + trie->data_size, value, + trie->map.value_size); + + return node; +} + +/* Called from syscall or from eBPF program */ +static int trie_update_elem(struct bpf_map *map, + void *_key, void *value, u64 flags) +{ + struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL; + struct lpm_trie_node __rcu **slot; + struct bpf_lpm_trie_key *key = _key; + unsigned long irq_flags; + unsigned int next_bit; + size_t matchlen = 0; + int ret = 0; + + if (unlikely(flags > BPF_EXIST)) + return -EINVAL; + + if (key->prefixlen > trie->max_prefixlen) + return -EINVAL; + + raw_spin_lock_irqsave(&trie->lock, irq_flags); + + /* Allocate and fill a new node */ + + if (trie->n_entries == trie->map.max_entries) { + ret = -ENOSPC; + goto out; + } + + new_node = lpm_trie_node_alloc(trie, value); + if (!new_node) { + ret = -ENOMEM; + goto out; + } + + trie->n_entries++; + + new_node->prefixlen = key->prefixlen; + RCU_INIT_POINTER(new_node->child[0], NULL); + RCU_INIT_POINTER(new_node->child[1], NULL); + memcpy(new_node->data, key->data, trie->data_size); + + /* Now find a slot to attach the new node. To do that, walk the tree + * from the root and match as many bits as possible for each node until + * we either find an empty slot or a slot that needs to be replaced by + * an intermediate node. + */ + slot = &trie->root; + + while ((node = rcu_dereference_protected(*slot, + lockdep_is_held(&trie->lock)))) { + matchlen = longest_prefix_match(trie, node, key); + + if (node->prefixlen != matchlen || + node->prefixlen == key->prefixlen || + node->prefixlen == trie->max_prefixlen) + break; + + next_bit = extract_bit(key->data, node->prefixlen); + slot = &node->child[next_bit]; + } + + /* If the slot is empty (a free child pointer or an empty root), + * simply assign the @new_node to that slot and be done. + */ + if (!node) { + rcu_assign_pointer(*slot, new_node); + goto out; + } + + /* If the slot we picked already exists, replace it with @new_node + * which already has the correct data array set. + */ + if (node->prefixlen == matchlen) { + new_node->child[0] = node->child[0]; + new_node->child[1] = node->child[1]; + + if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) + trie->n_entries--; + + rcu_assign_pointer(*slot, new_node); + kfree_rcu(node, rcu); + + goto out; + } + + /* If the new node matches the prefix completely, it must be inserted + * as an ancestor. Simply insert it between @node and *@slot. + */ + if (matchlen == key->prefixlen) { + next_bit = extract_bit(node->data, matchlen); + rcu_assign_pointer(new_node->child[next_bit], node); + rcu_assign_pointer(*slot, new_node); + goto out; + } + + im_node = lpm_trie_node_alloc(trie, NULL); + if (!im_node) { + ret = -ENOMEM; + goto out; + } + + im_node->prefixlen = matchlen; + im_node->flags |= LPM_TREE_NODE_FLAG_IM; + memcpy(im_node->data, node->data, trie->data_size); + + /* Now determine which child to install in which slot */ + if (extract_bit(key->data, matchlen)) { + rcu_assign_pointer(im_node->child[0], node); + rcu_assign_pointer(im_node->child[1], new_node); + } else { + rcu_assign_pointer(im_node->child[0], new_node); + rcu_assign_pointer(im_node->child[1], node); + } + + /* Finally, assign the intermediate node to the determined spot */ + rcu_assign_pointer(*slot, im_node); + +out: + if (ret) { + if (new_node) + trie->n_entries--; + + kfree(new_node); + kfree(im_node); + } + + raw_spin_unlock_irqrestore(&trie->lock, irq_flags); + + return ret; +} + +/* Called from syscall or from eBPF program */ +static int trie_delete_elem(struct bpf_map *map, void *_key) +{ + struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct bpf_lpm_trie_key *key = _key; + struct lpm_trie_node __rcu **trim, **trim2; + struct lpm_trie_node *node, *parent; + unsigned long irq_flags; + unsigned int next_bit; + size_t matchlen = 0; + int ret = 0; + + if (key->prefixlen > trie->max_prefixlen) + return -EINVAL; + + raw_spin_lock_irqsave(&trie->lock, irq_flags); + + /* Walk the tree looking for an exact key/length match and keeping + * track of the path we traverse. We will need to know the node + * we wish to delete, and the slot that points to the node we want + * to delete. We may also need to know the nodes parent and the + * slot that contains it. + */ + trim = &trie->root; + trim2 = trim; + parent = NULL; + while ((node = rcu_dereference_protected( + *trim, lockdep_is_held(&trie->lock)))) { + matchlen = longest_prefix_match(trie, node, key); + + if (node->prefixlen != matchlen || + node->prefixlen == key->prefixlen) + break; + + parent = node; + trim2 = trim; + next_bit = extract_bit(key->data, node->prefixlen); + trim = &node->child[next_bit]; + } + + if (!node || node->prefixlen != key->prefixlen || + node->prefixlen != matchlen || + (node->flags & LPM_TREE_NODE_FLAG_IM)) { + ret = -ENOENT; + goto out; + } + + trie->n_entries--; + + /* If the node we are removing has two children, simply mark it + * as intermediate and we are done. + */ + if (rcu_access_pointer(node->child[0]) && + rcu_access_pointer(node->child[1])) { + node->flags |= LPM_TREE_NODE_FLAG_IM; + goto out; + } + + /* If the parent of the node we are about to delete is an intermediate + * node, and the deleted node doesn't have any children, we can delete + * the intermediate parent as well and promote its other child + * up the tree. Doing this maintains the invariant that all + * intermediate nodes have exactly 2 children and that there are no + * unnecessary intermediate nodes in the tree. + */ + if (parent && (parent->flags & LPM_TREE_NODE_FLAG_IM) && + !node->child[0] && !node->child[1]) { + if (node == rcu_access_pointer(parent->child[0])) + rcu_assign_pointer( + *trim2, rcu_access_pointer(parent->child[1])); + else + rcu_assign_pointer( + *trim2, rcu_access_pointer(parent->child[0])); + kfree_rcu(parent, rcu); + kfree_rcu(node, rcu); + goto out; + } + + /* The node we are removing has either zero or one child. If there + * is a child, move it into the removed node's slot then delete + * the node. Otherwise just clear the slot and delete the node. + */ + if (node->child[0]) + rcu_assign_pointer(*trim, rcu_access_pointer(node->child[0])); + else if (node->child[1]) + rcu_assign_pointer(*trim, rcu_access_pointer(node->child[1])); + else + RCU_INIT_POINTER(*trim, NULL); + kfree_rcu(node, rcu); + +out: + raw_spin_unlock_irqrestore(&trie->lock, irq_flags); + + return ret; +} + +#define LPM_DATA_SIZE_MAX 256 +#define LPM_DATA_SIZE_MIN 1 + +#define LPM_VAL_SIZE_MAX (KMALLOC_MAX_SIZE - LPM_DATA_SIZE_MAX - \ + sizeof(struct lpm_trie_node)) +#define LPM_VAL_SIZE_MIN 1 + +#define LPM_KEY_SIZE(X) (sizeof(struct bpf_lpm_trie_key) + (X)) +#define LPM_KEY_SIZE_MAX LPM_KEY_SIZE(LPM_DATA_SIZE_MAX) +#define LPM_KEY_SIZE_MIN LPM_KEY_SIZE(LPM_DATA_SIZE_MIN) + +#define LPM_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_NUMA_NODE | \ + BPF_F_RDONLY | BPF_F_WRONLY) + +static struct bpf_map *trie_alloc(union bpf_attr *attr) +{ + struct lpm_trie *trie; + u64 cost = sizeof(*trie), cost_per_node; + int ret; + + if (!capable(CAP_SYS_ADMIN)) + return ERR_PTR(-EPERM); + + /* check sanity of attributes */ + if (attr->max_entries == 0 || + !(attr->map_flags & BPF_F_NO_PREALLOC) || + attr->map_flags & ~LPM_CREATE_FLAG_MASK || + attr->key_size < LPM_KEY_SIZE_MIN || + attr->key_size > LPM_KEY_SIZE_MAX || + attr->value_size < LPM_VAL_SIZE_MIN || + attr->value_size > LPM_VAL_SIZE_MAX) + return ERR_PTR(-EINVAL); + + trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN); + if (!trie) + return ERR_PTR(-ENOMEM); + + /* copy mandatory map attributes */ + bpf_map_init_from_attr(&trie->map, attr); + trie->data_size = attr->key_size - + offsetof(struct bpf_lpm_trie_key, data); + trie->max_prefixlen = trie->data_size * 8; + + cost_per_node = sizeof(struct lpm_trie_node) + + attr->value_size + trie->data_size; + cost += (u64) attr->max_entries * cost_per_node; + if (cost >= U32_MAX - PAGE_SIZE) { + ret = -E2BIG; + goto out_err; + } + + trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT; + + ret = bpf_map_precharge_memlock(trie->map.pages); + if (ret) + goto out_err; + + raw_spin_lock_init(&trie->lock); + + return &trie->map; +out_err: + kfree(trie); + return ERR_PTR(ret); +} + +static void trie_free(struct bpf_map *map) +{ + struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct lpm_trie_node __rcu **slot; + struct lpm_trie_node *node; + + /* Wait for outstanding programs to complete + * update/lookup/delete/get_next_key and free the trie. + */ + synchronize_rcu(); + + /* Always start at the root and walk down to a node that has no + * children. Then free that node, nullify its reference in the parent + * and start over. + */ + + for (;;) { + slot = &trie->root; + + for (;;) { + node = rcu_dereference_protected(*slot, 1); + if (!node) + goto out; + + if (rcu_access_pointer(node->child[0])) { + slot = &node->child[0]; + continue; + } + + if (rcu_access_pointer(node->child[1])) { + slot = &node->child[1]; + continue; + } + + kfree(node); + RCU_INIT_POINTER(*slot, NULL); + break; + } + } + +out: + kfree(trie); +} + +static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key) +{ + struct lpm_trie_node *node, *next_node = NULL, *parent, *search_root; + struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct bpf_lpm_trie_key *key = _key, *next_key = _next_key; + struct lpm_trie_node **node_stack = NULL; + int err = 0, stack_ptr = -1; + unsigned int next_bit; + size_t matchlen; + + /* The get_next_key follows postorder. For the 4 node example in + * the top of this file, the trie_get_next_key() returns the following + * one after another: + * 192.168.0.0/24 + * 192.168.1.0/24 + * 192.168.128.0/24 + * 192.168.0.0/16 + * + * The idea is to return more specific keys before less specific ones. + */ + + /* Empty trie */ + search_root = rcu_dereference(trie->root); + if (!search_root) + return -ENOENT; + + /* For invalid key, find the leftmost node in the trie */ + if (!key || key->prefixlen > trie->max_prefixlen) + goto find_leftmost; + + node_stack = kmalloc_array(trie->max_prefixlen, + sizeof(struct lpm_trie_node *), + GFP_ATOMIC | __GFP_NOWARN); + if (!node_stack) + return -ENOMEM; + + /* Try to find the exact node for the given key */ + for (node = search_root; node;) { + node_stack[++stack_ptr] = node; + matchlen = longest_prefix_match(trie, node, key); + if (node->prefixlen != matchlen || + node->prefixlen == key->prefixlen) + break; + + next_bit = extract_bit(key->data, node->prefixlen); + node = rcu_dereference(node->child[next_bit]); + } + if (!node || node->prefixlen != key->prefixlen || + (node->flags & LPM_TREE_NODE_FLAG_IM)) + goto find_leftmost; + + /* The node with the exactly-matching key has been found, + * find the first node in postorder after the matched node. + */ + node = node_stack[stack_ptr]; + while (stack_ptr > 0) { + parent = node_stack[stack_ptr - 1]; + if (rcu_dereference(parent->child[0]) == node) { + search_root = rcu_dereference(parent->child[1]); + if (search_root) + goto find_leftmost; + } + if (!(parent->flags & LPM_TREE_NODE_FLAG_IM)) { + next_node = parent; + goto do_copy; + } + + node = parent; + stack_ptr--; + } + + /* did not find anything */ + err = -ENOENT; + goto free_stack; + +find_leftmost: + /* Find the leftmost non-intermediate node, all intermediate nodes + * have exact two children, so this function will never return NULL. + */ + for (node = search_root; node;) { + if (node->flags & LPM_TREE_NODE_FLAG_IM) { + node = rcu_dereference(node->child[0]); + } else { + next_node = node; + node = rcu_dereference(node->child[0]); + if (!node) + node = rcu_dereference(next_node->child[1]); + } + } +do_copy: + next_key->prefixlen = next_node->prefixlen; + memcpy((void *)next_key + offsetof(struct bpf_lpm_trie_key, data), + next_node->data, trie->data_size); +free_stack: + kfree(node_stack); + return err; +} + +static int trie_check_btf(const struct bpf_map *map, + const struct btf_type *key_type, + const struct btf_type *value_type) +{ + /* Keys must have struct bpf_lpm_trie_key embedded. */ + return BTF_INFO_KIND(key_type->info) != BTF_KIND_STRUCT ? + -EINVAL : 0; +} + +const struct bpf_map_ops trie_map_ops = { + .map_alloc = trie_alloc, + .map_free = trie_free, + .map_get_next_key = trie_get_next_key, + .map_lookup_elem = trie_lookup_elem, + .map_update_elem = trie_update_elem, + .map_delete_elem = trie_delete_elem, + .map_check_btf = trie_check_btf, +}; |