--- /dev/null
+/*
+ * 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/err.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/vmalloc.h>
+#include <net/ipv6.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(size, GFP_ATOMIC | __GFP_NOWARN);
+ 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, *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;
+}
+
+static int trie_delete_elem(struct bpf_map *map, void *key)
+{
+ /* TODO */
+ return -ENOSYS;
+}
+
+static struct bpf_map *trie_alloc(union bpf_attr *attr)
+{
+ size_t cost, cost_per_node;
+ struct lpm_trie *trie;
+ 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->key_size < sizeof(struct bpf_lpm_trie_key) + 1 ||
+ attr->key_size > sizeof(struct bpf_lpm_trie_key) + 256 ||
+ attr->value_size == 0)
+ return ERR_PTR(-EINVAL);
+
+ trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN);
+ if (!trie)
+ return ERR_PTR(-ENOMEM);
+
+ /* copy mandatory map attributes */
+ trie->map.map_type = attr->map_type;
+ trie->map.key_size = attr->key_size;
+ trie->map.value_size = attr->value_size;
+ trie->map.max_entries = attr->max_entries;
+ 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 = sizeof(*trie) + attr->max_entries * cost_per_node;
+ trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
+
+ ret = bpf_map_precharge_memlock(trie->map.pages);
+ if (ret) {
+ kfree(trie);
+ return ERR_PTR(ret);
+ }
+
+ raw_spin_lock_init(&trie->lock);
+
+ return &trie->map;
+}
+
+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;
+
+ raw_spin_lock(&trie->lock);
+
+ /* 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,
+ lockdep_is_held(&trie->lock));
+ if (!node)
+ goto unlock;
+
+ 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;
+ }
+ }
+
+unlock:
+ raw_spin_unlock(&trie->lock);
+}
+
+static const struct bpf_map_ops trie_ops = {
+ .map_alloc = trie_alloc,
+ .map_free = trie_free,
+ .map_lookup_elem = trie_lookup_elem,
+ .map_update_elem = trie_update_elem,
+ .map_delete_elem = trie_delete_elem,
+};
+
+static struct bpf_map_type_list trie_type __read_mostly = {
+ .ops = &trie_ops,
+ .type = BPF_MAP_TYPE_LPM_TRIE,
+};
+
+static int __init register_trie_map(void)
+{
+ bpf_register_map_type(&trie_type);
+ return 0;
+}
+late_initcall(register_trie_map);
git.samba.org / sfrench / cifs-2.6.git / commitdiff