Merge branch 'bpf-lpm'

Daniel Mack says:

====================
bpf: add longest prefix match map

This patch set adds a longest prefix match algorithm that can be used
to match IP addresses to a stored set of ranges. It is exposed as a
bpf map type.

Internally, data is stored in an unbalanced tree of nodes that has a
maximum height of n, where n is the prefixlen the trie was created
with.

Note that this has nothing to do with fib or fib6 and is in no way meant
to replace or share code with it. It's rather a much simpler
implementation that is specifically written with bpf maps in mind.

Patch 1/2 adds the implementation, 2/2 an extensive test suite and 3/3
has benchmarking code for the new trie type.

Feedback is much appreciated.

Changelog:

v3 -> v4:
	* David added a 3rd patch that augments map_perf_test for
	  LPM trie benchmarks
	* Limit allocation of maps of this new type to CAP_SYS_ADMIN
	  for now, as requested by Alexei
	* Add a stub .map_delete_elem so the core does not stumble
	  over a NULL pointer when the syscall is invoked
	* Tests for non-power-of-2 prefix lengths were added
	* More comment style fixes

v2 -> v3:
	* Store both the key match data and the caller provided
	  value in the same byte array attached to a node. This
	  avoids double allocations
	* Bring back node->flags to distinguish between 'real'
	  and intermediate nodes
	* Fix comment style and some typos

v1 -> v2:
	* Turn spin lock into raw spinlock
	* Lock with irqsave options during trie_update_elem()
	* Return -ENOMEM properly from trie_alloc()
	* Force attr->flags == BPF_F_NO_PREALLOC during creation
	* Set trie->map.pages after creation to account for map memory
	* Allow arbitrary value sizes
	* Removed node->flags and denode intermediate nodes through
	  node->value == NULL instead

rfc -> v1:
	* Add __rcu pointer annotations to make sparse happy
	* Fold _lpm_trie_find_target_node() into its only caller
	* Fix some minor documentation issues
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 504 insertions, 1 deletions

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 1276474ac3cd..e1ce4f4fd7fd 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -1,7 +1,7 @@
 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
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
new file mode 100644
index 000000000000..ba19241d1979
--- /dev/null
+++ b/kernel/bpf/lpm_trie.c
@@ -0,0 +1,503 @@
+/*
+ * 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);