linux/kernel/bpf/lpm_trie.c
Andrii Nakryiko 6c3eba1c5e bpf: Centralize permissions checks for all BPF map types
This allows to do more centralized decisions later on, and generally
makes it very explicit which maps are privileged and which are not
(e.g., LRU_HASH and LRU_PERCPU_HASH, which are privileged HASH variants,
as opposed to unprivileged HASH and HASH_PERCPU; now this is explicit
and easy to verify).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230613223533.3689589-4-andrii@kernel.org
2023-06-19 14:04:04 +02:00

746 lines
21 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Longest prefix match list implementation
*
* Copyright (c) 2016,2017 Daniel Mack
* Copyright (c) 2016 David Herrmann
*/
#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>
#include <linux/btf_ids.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[];
};
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;
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)
{
u32 limit = min(node->prefixlen, key->prefixlen);
u32 prefixlen = 0, i = 0;
BUILD_BUG_ON(offsetof(struct lpm_trie_node, data) % sizeof(u32));
BUILD_BUG_ON(offsetof(struct bpf_lpm_trie_key, data) % sizeof(u32));
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && defined(CONFIG_64BIT)
/* data_size >= 16 has very small probability.
* We do not use a loop for optimal code generation.
*/
if (trie->data_size >= 8) {
u64 diff = be64_to_cpu(*(__be64 *)node->data ^
*(__be64 *)key->data);
prefixlen = 64 - fls64(diff);
if (prefixlen >= limit)
return limit;
if (diff)
return prefixlen;
i = 8;
}
#endif
while (trie->data_size >= i + 4) {
u32 diff = be32_to_cpu(*(__be32 *)&node->data[i] ^
*(__be32 *)&key->data[i]);
prefixlen += 32 - fls(diff);
if (prefixlen >= limit)
return limit;
if (diff)
return prefixlen;
i += 4;
}
if (trie->data_size >= i + 2) {
u16 diff = be16_to_cpu(*(__be16 *)&node->data[i] ^
*(__be16 *)&key->data[i]);
prefixlen += 16 - fls(diff);
if (prefixlen >= limit)
return limit;
if (diff)
return prefixlen;
i += 2;
}
if (trie->data_size >= i + 1) {
prefixlen += 8 - fls(node->data[i] ^ key->data[i]);
if (prefixlen >= limit)
return limit;
}
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_check(trie->root, rcu_read_lock_bh_held());
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_check(node->child[next_bit],
rcu_read_lock_bh_held());
}
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 = bpf_map_kmalloc_node(&trie->map, size, GFP_NOWAIT | __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 long 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;
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 slot */
rcu_assign_pointer(*slot, im_node);
out:
if (ret) {
if (new_node)
trie->n_entries--;
kfree(new_node);
kfree(im_node);
}
spin_unlock_irqrestore(&trie->lock, irq_flags);
return ret;
}
/* Called from syscall or from eBPF program */
static long 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;
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:
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_ACCESS_MASK)
static struct bpf_map *trie_alloc(union bpf_attr *attr)
{
struct lpm_trie *trie;
/* check sanity of attributes */
if (attr->max_entries == 0 ||
!(attr->map_flags & BPF_F_NO_PREALLOC) ||
attr->map_flags & ~LPM_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags) ||
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 = bpf_map_area_alloc(sizeof(*trie), NUMA_NO_NODE);
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;
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;
/* 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:
bpf_map_area_free(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 *btf,
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;
}
static u64 trie_mem_usage(const struct bpf_map *map)
{
struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
u64 elem_size;
elem_size = sizeof(struct lpm_trie_node) + trie->data_size +
trie->map.value_size;
return elem_size * READ_ONCE(trie->n_entries);
}
BTF_ID_LIST_SINGLE(trie_map_btf_ids, struct, lpm_trie)
const struct bpf_map_ops trie_map_ops = {
.map_meta_equal = bpf_map_meta_equal,
.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_lookup_batch = generic_map_lookup_batch,
.map_update_batch = generic_map_update_batch,
.map_delete_batch = generic_map_delete_batch,
.map_check_btf = trie_check_btf,
.map_mem_usage = trie_mem_usage,
.map_btf_id = &trie_map_btf_ids[0],
};