bpf: add a longest prefix match trie map implementation

	__s32	imm;		/* signed immediate constant */

};

/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */

struct bpf_lpm_trie_key {

	__u32	prefixlen;	/* up to 32 for AF_INET, 128 for AF_INET6 */

	__u8	data[0];	/* Arbitrary size */

};

/* BPF syscall commands, see bpf(2) man-page for details. */

enum bpf_cmd {

	BPF_MAP_CREATE,

	BPF_MAP_TYPE_CGROUP_ARRAY,

	BPF_MAP_TYPE_LRU_HASH,

	BPF_MAP_TYPE_LRU_PERCPU_HASH,

	BPF_MAP_TYPE_LPM_TRIE,

};

enum bpf_prog_type {

obj-y := core.o

obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o

obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o

obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o

ifeq ($(CONFIG_PERF_EVENTS),y)

obj-$(CONFIG_BPF_SYSCALL) += stackmap.o

endif

/*

 * 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);