1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (c) 2021 Facebook */
3
4#include <linux/bitmap.h>
5#include <linux/bpf.h>
6#include <linux/btf.h>
7#include <linux/err.h>
8#include <linux/jhash.h>
9#include <linux/random.h>
10#include <linux/btf_ids.h>
11
12#define BLOOM_CREATE_FLAG_MASK \
13	(BPF_F_NUMA_NODE | BPF_F_ZERO_SEED | BPF_F_ACCESS_MASK)
14
15struct bpf_bloom_filter {
16	struct bpf_map map;
17	u32 bitset_mask;
18	u32 hash_seed;
19	u32 nr_hash_funcs;
20	unsigned long bitset[];
21};
22
23static u32 hash(struct bpf_bloom_filter *bloom, void *value,
24		u32 value_size, u32 index)
25{
26	u32 h;
27
28	if (likely(value_size % 4 == 0))
29		h = jhash2(value, value_size / 4, bloom->hash_seed + index);
30	else
31		h = jhash(value, value_size, bloom->hash_seed + index);
32
33	return h & bloom->bitset_mask;
34}
35
36static long bloom_map_peek_elem(struct bpf_map *map, void *value)
37{
38	struct bpf_bloom_filter *bloom =
39		container_of(map, struct bpf_bloom_filter, map);
40	u32 i, h;
41
42	for (i = 0; i < bloom->nr_hash_funcs; i++) {
43		h = hash(bloom, value, map->value_size, i);
44		if (!test_bit(h, bloom->bitset))
45			return -ENOENT;
46	}
47
48	return 0;
49}
50
51static long bloom_map_push_elem(struct bpf_map *map, void *value, u64 flags)
52{
53	struct bpf_bloom_filter *bloom =
54		container_of(map, struct bpf_bloom_filter, map);
55	u32 i, h;
56
57	if (flags != BPF_ANY)
58		return -EINVAL;
59
60	for (i = 0; i < bloom->nr_hash_funcs; i++) {
61		h = hash(bloom, value, map->value_size, i);
62		set_bit(h, bloom->bitset);
63	}
64
65	return 0;
66}
67
68static long bloom_map_pop_elem(struct bpf_map *map, void *value)
69{
70	return -EOPNOTSUPP;
71}
72
73static long bloom_map_delete_elem(struct bpf_map *map, void *value)
74{
75	return -EOPNOTSUPP;
76}
77
78static int bloom_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
79{
80	return -EOPNOTSUPP;
81}
82
83static struct bpf_map *bloom_map_alloc(union bpf_attr *attr)
84{
85	u32 bitset_bytes, bitset_mask, nr_hash_funcs, nr_bits;
86	int numa_node = bpf_map_attr_numa_node(attr);
87	struct bpf_bloom_filter *bloom;
88
89	if (attr->key_size != 0 || attr->value_size == 0 ||
90	    attr->max_entries == 0 ||
91	    attr->map_flags & ~BLOOM_CREATE_FLAG_MASK ||
92	    !bpf_map_flags_access_ok(attr->map_flags) ||
93	    /* The lower 4 bits of map_extra (0xF) specify the number
94	     * of hash functions
95	     */
96	    (attr->map_extra & ~0xF))
97		return ERR_PTR(-EINVAL);
98
99	nr_hash_funcs = attr->map_extra;
100	if (nr_hash_funcs == 0)
101		/* Default to using 5 hash functions if unspecified */
102		nr_hash_funcs = 5;
103
104	/* For the bloom filter, the optimal bit array size that minimizes the
105	 * false positive probability is n * k / ln(2) where n is the number of
106	 * expected entries in the bloom filter and k is the number of hash
107	 * functions. We use 7 / 5 to approximate 1 / ln(2).
108	 *
109	 * We round this up to the nearest power of two to enable more efficient
110	 * hashing using bitmasks. The bitmask will be the bit array size - 1.
111	 *
112	 * If this overflows a u32, the bit array size will have 2^32 (4
113	 * GB) bits.
114	 */
115	if (check_mul_overflow(attr->max_entries, nr_hash_funcs, &nr_bits) ||
116	    check_mul_overflow(nr_bits / 5, (u32)7, &nr_bits) ||
117	    nr_bits > (1UL << 31)) {
118		/* The bit array size is 2^32 bits but to avoid overflowing the
119		 * u32, we use U32_MAX, which will round up to the equivalent
120		 * number of bytes
121		 */
122		bitset_bytes = BITS_TO_BYTES(U32_MAX);
123		bitset_mask = U32_MAX;
124	} else {
125		if (nr_bits <= BITS_PER_LONG)
126			nr_bits = BITS_PER_LONG;
127		else
128			nr_bits = roundup_pow_of_two(nr_bits);
129		bitset_bytes = BITS_TO_BYTES(nr_bits);
130		bitset_mask = nr_bits - 1;
131	}
132
133	bitset_bytes = roundup(bitset_bytes, sizeof(unsigned long));
134	bloom = bpf_map_area_alloc(sizeof(*bloom) + bitset_bytes, numa_node);
135
136	if (!bloom)
137		return ERR_PTR(-ENOMEM);
138
139	bpf_map_init_from_attr(&bloom->map, attr);
140
141	bloom->nr_hash_funcs = nr_hash_funcs;
142	bloom->bitset_mask = bitset_mask;
143
144	if (!(attr->map_flags & BPF_F_ZERO_SEED))
145		bloom->hash_seed = get_random_u32();
146
147	return &bloom->map;
148}
149
150static void bloom_map_free(struct bpf_map *map)
151{
152	struct bpf_bloom_filter *bloom =
153		container_of(map, struct bpf_bloom_filter, map);
154
155	bpf_map_area_free(bloom);
156}
157
158static void *bloom_map_lookup_elem(struct bpf_map *map, void *key)
159{
160	/* The eBPF program should use map_peek_elem instead */
161	return ERR_PTR(-EINVAL);
162}
163
164static long bloom_map_update_elem(struct bpf_map *map, void *key,
165				  void *value, u64 flags)
166{
167	/* The eBPF program should use map_push_elem instead */
168	return -EINVAL;
169}
170
171static int bloom_map_check_btf(const struct bpf_map *map,
172			       const struct btf *btf,
173			       const struct btf_type *key_type,
174			       const struct btf_type *value_type)
175{
176	/* Bloom filter maps are keyless */
177	return btf_type_is_void(key_type) ? 0 : -EINVAL;
178}
179
180static u64 bloom_map_mem_usage(const struct bpf_map *map)
181{
182	struct bpf_bloom_filter *bloom;
183	u64 bitset_bytes;
184
185	bloom = container_of(map, struct bpf_bloom_filter, map);
186	bitset_bytes = BITS_TO_BYTES((u64)bloom->bitset_mask + 1);
187	bitset_bytes = roundup(bitset_bytes, sizeof(unsigned long));
188	return sizeof(*bloom) + bitset_bytes;
189}
190
191BTF_ID_LIST_SINGLE(bpf_bloom_map_btf_ids, struct, bpf_bloom_filter)
192const struct bpf_map_ops bloom_filter_map_ops = {
193	.map_meta_equal = bpf_map_meta_equal,
194	.map_alloc = bloom_map_alloc,
195	.map_free = bloom_map_free,
196	.map_get_next_key = bloom_map_get_next_key,
197	.map_push_elem = bloom_map_push_elem,
198	.map_peek_elem = bloom_map_peek_elem,
199	.map_pop_elem = bloom_map_pop_elem,
200	.map_lookup_elem = bloom_map_lookup_elem,
201	.map_update_elem = bloom_map_update_elem,
202	.map_delete_elem = bloom_map_delete_elem,
203	.map_check_btf = bloom_map_check_btf,
204	.map_mem_usage = bloom_map_mem_usage,
205	.map_btf_id = &bpf_bloom_map_btf_ids[0],
206};
207