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	/* If the size of the values in the bloom filter is u32 aligned,
20	 * then it is more performant to use jhash2 as the underlying hash
21	 * function, else we use jhash. This tracks the number of u32s
22	 * in an u32-aligned value size. If the value size is not u32 aligned,
23	 * this will be 0.
24	 */
25	u32 aligned_u32_count;
26	u32 nr_hash_funcs;
27	unsigned long bitset[];
28};
29
30static u32 hash(struct bpf_bloom_filter *bloom, void *value,
31		u32 value_size, u32 index)
32{
33	u32 h;
34
35	if (bloom->aligned_u32_count)
36		h = jhash2(value, bloom->aligned_u32_count,
37			   bloom->hash_seed + index);
38	else
39		h = jhash(value, value_size, bloom->hash_seed + index);
40
41	return h & bloom->bitset_mask;
42}
43
44static int bloom_map_peek_elem(struct bpf_map *map, void *value)
45{
46	struct bpf_bloom_filter *bloom =
47		container_of(map, struct bpf_bloom_filter, map);
48	u32 i, h;
49
50	for (i = 0; i < bloom->nr_hash_funcs; i++) {
51		h = hash(bloom, value, map->value_size, i);
52		if (!test_bit(h, bloom->bitset))
53			return -ENOENT;
54	}
55
56	return 0;
57}
58
59static int bloom_map_push_elem(struct bpf_map *map, void *value, u64 flags)
60{
61	struct bpf_bloom_filter *bloom =
62		container_of(map, struct bpf_bloom_filter, map);
63	u32 i, h;
64
65	if (flags != BPF_ANY)
66		return -EINVAL;
67
68	for (i = 0; i < bloom->nr_hash_funcs; i++) {
69		h = hash(bloom, value, map->value_size, i);
70		set_bit(h, bloom->bitset);
71	}
72
73	return 0;
74}
75
76static int bloom_map_pop_elem(struct bpf_map *map, void *value)
77{
78	return -EOPNOTSUPP;
79}
80
81static int bloom_map_delete_elem(struct bpf_map *map, void *value)
82{
83	return -EOPNOTSUPP;
84}
85
86static int bloom_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
87{
88	return -EOPNOTSUPP;
89}
90
91static struct bpf_map *bloom_map_alloc(union bpf_attr *attr)
92{
93	u32 bitset_bytes, bitset_mask, nr_hash_funcs, nr_bits;
94	int numa_node = bpf_map_attr_numa_node(attr);
95	struct bpf_bloom_filter *bloom;
96
97	if (!bpf_capable())
98		return ERR_PTR(-EPERM);
99
100	if (attr->key_size != 0 || attr->value_size == 0 ||
101	    attr->max_entries == 0 ||
102	    attr->map_flags & ~BLOOM_CREATE_FLAG_MASK ||
103	    !bpf_map_flags_access_ok(attr->map_flags) ||
104	    /* The lower 4 bits of map_extra (0xF) specify the number
105	     * of hash functions
106	     */
107	    (attr->map_extra & ~0xF))
108		return ERR_PTR(-EINVAL);
109
110	nr_hash_funcs = attr->map_extra;
111	if (nr_hash_funcs == 0)
112		/* Default to using 5 hash functions if unspecified */
113		nr_hash_funcs = 5;
114
115	/* For the bloom filter, the optimal bit array size that minimizes the
116	 * false positive probability is n * k / ln(2) where n is the number of
117	 * expected entries in the bloom filter and k is the number of hash
118	 * functions. We use 7 / 5 to approximate 1 / ln(2).
119	 *
120	 * We round this up to the nearest power of two to enable more efficient
121	 * hashing using bitmasks. The bitmask will be the bit array size - 1.
122	 *
123	 * If this overflows a u32, the bit array size will have 2^32 (4
124	 * GB) bits.
125	 */
126	if (check_mul_overflow(attr->max_entries, nr_hash_funcs, &nr_bits) ||
127	    check_mul_overflow(nr_bits / 5, (u32)7, &nr_bits) ||
128	    nr_bits > (1UL << 31)) {
129		/* The bit array size is 2^32 bits but to avoid overflowing the
130		 * u32, we use U32_MAX, which will round up to the equivalent
131		 * number of bytes
132		 */
133		bitset_bytes = BITS_TO_BYTES(U32_MAX);
134		bitset_mask = U32_MAX;
135	} else {
136		if (nr_bits <= BITS_PER_LONG)
137			nr_bits = BITS_PER_LONG;
138		else
139			nr_bits = roundup_pow_of_two(nr_bits);
140		bitset_bytes = BITS_TO_BYTES(nr_bits);
141		bitset_mask = nr_bits - 1;
142	}
143
144	bitset_bytes = roundup(bitset_bytes, sizeof(unsigned long));
145	bloom = bpf_map_area_alloc(sizeof(*bloom) + bitset_bytes, numa_node);
146
147	if (!bloom)
148		return ERR_PTR(-ENOMEM);
149
150	bpf_map_init_from_attr(&bloom->map, attr);
151
152	bloom->nr_hash_funcs = nr_hash_funcs;
153	bloom->bitset_mask = bitset_mask;
154
155	/* Check whether the value size is u32-aligned */
156	if ((attr->value_size & (sizeof(u32) - 1)) == 0)
157		bloom->aligned_u32_count =
158			attr->value_size / sizeof(u32);
159
160	if (!(attr->map_flags & BPF_F_ZERO_SEED))
161		bloom->hash_seed = get_random_int();
162
163	return &bloom->map;
164}
165
166static void bloom_map_free(struct bpf_map *map)
167{
168	struct bpf_bloom_filter *bloom =
169		container_of(map, struct bpf_bloom_filter, map);
170
171	bpf_map_area_free(bloom);
172}
173
174static void *bloom_map_lookup_elem(struct bpf_map *map, void *key)
175{
176	/* The eBPF program should use map_peek_elem instead */
177	return ERR_PTR(-EINVAL);
178}
179
180static int bloom_map_update_elem(struct bpf_map *map, void *key,
181				 void *value, u64 flags)
182{
183	/* The eBPF program should use map_push_elem instead */
184	return -EINVAL;
185}
186
187static int bloom_map_check_btf(const struct bpf_map *map,
188			       const struct btf *btf,
189			       const struct btf_type *key_type,
190			       const struct btf_type *value_type)
191{
192	/* Bloom filter maps are keyless */
193	return btf_type_is_void(key_type) ? 0 : -EINVAL;
194}
195
196BTF_ID_LIST_SINGLE(bpf_bloom_map_btf_ids, struct, bpf_bloom_filter)
197const struct bpf_map_ops bloom_filter_map_ops = {
198	.map_meta_equal = bpf_map_meta_equal,
199	.map_alloc = bloom_map_alloc,
200	.map_free = bloom_map_free,
201	.map_get_next_key = bloom_map_get_next_key,
202	.map_push_elem = bloom_map_push_elem,
203	.map_peek_elem = bloom_map_peek_elem,
204	.map_pop_elem = bloom_map_pop_elem,
205	.map_lookup_elem = bloom_map_lookup_elem,
206	.map_update_elem = bloom_map_update_elem,
207	.map_delete_elem = bloom_map_delete_elem,
208	.map_check_btf = bloom_map_check_btf,
209	.map_btf_id = &bpf_bloom_map_btf_ids[0],
210};
211