summaryrefslogtreecommitdiff
path: root/kernel/bpf/bloom_filter.c
blob: b141a1346f72dd6d1535fed97f76da97a4a475b3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2021 Facebook */

#include <linux/bitmap.h>
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/err.h>
#include <linux/jhash.h>
#include <linux/random.h>

#define BLOOM_CREATE_FLAG_MASK \
	(BPF_F_NUMA_NODE | BPF_F_ZERO_SEED | BPF_F_ACCESS_MASK)

struct bpf_bloom_filter {
	struct bpf_map map;
	u32 bitset_mask;
	u32 hash_seed;
	/* If the size of the values in the bloom filter is u32 aligned,
	 * then it is more performant to use jhash2 as the underlying hash
	 * function, else we use jhash. This tracks the number of u32s
	 * in an u32-aligned value size. If the value size is not u32 aligned,
	 * this will be 0.
	 */
	u32 aligned_u32_count;
	u32 nr_hash_funcs;
	unsigned long bitset[];
};

static u32 hash(struct bpf_bloom_filter *bloom, void *value,
		u32 value_size, u32 index)
{
	u32 h;

	if (bloom->aligned_u32_count)
		h = jhash2(value, bloom->aligned_u32_count,
			   bloom->hash_seed + index);
	else
		h = jhash(value, value_size, bloom->hash_seed + index);

	return h & bloom->bitset_mask;
}

static int bloom_map_peek_elem(struct bpf_map *map, void *value)
{
	struct bpf_bloom_filter *bloom =
		container_of(map, struct bpf_bloom_filter, map);
	u32 i, h;

	for (i = 0; i < bloom->nr_hash_funcs; i++) {
		h = hash(bloom, value, map->value_size, i);
		if (!test_bit(h, bloom->bitset))
			return -ENOENT;
	}

	return 0;
}

static int bloom_map_push_elem(struct bpf_map *map, void *value, u64 flags)
{
	struct bpf_bloom_filter *bloom =
		container_of(map, struct bpf_bloom_filter, map);
	u32 i, h;

	if (flags != BPF_ANY)
		return -EINVAL;

	for (i = 0; i < bloom->nr_hash_funcs; i++) {
		h = hash(bloom, value, map->value_size, i);
		set_bit(h, bloom->bitset);
	}

	return 0;
}

static int bloom_map_pop_elem(struct bpf_map *map, void *value)
{
	return -EOPNOTSUPP;
}

static int bloom_map_delete_elem(struct bpf_map *map, void *value)
{
	return -EOPNOTSUPP;
}

static int bloom_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
	return -EOPNOTSUPP;
}

static struct bpf_map *bloom_map_alloc(union bpf_attr *attr)
{
	u32 bitset_bytes, bitset_mask, nr_hash_funcs, nr_bits;
	int numa_node = bpf_map_attr_numa_node(attr);
	struct bpf_bloom_filter *bloom;

	if (!bpf_capable())
		return ERR_PTR(-EPERM);

	if (attr->key_size != 0 || attr->value_size == 0 ||
	    attr->max_entries == 0 ||
	    attr->map_flags & ~BLOOM_CREATE_FLAG_MASK ||
	    !bpf_map_flags_access_ok(attr->map_flags) ||
	    /* The lower 4 bits of map_extra (0xF) specify the number
	     * of hash functions
	     */
	    (attr->map_extra & ~0xF))
		return ERR_PTR(-EINVAL);

	nr_hash_funcs = attr->map_extra;
	if (nr_hash_funcs == 0)
		/* Default to using 5 hash functions if unspecified */
		nr_hash_funcs = 5;

	/* For the bloom filter, the optimal bit array size that minimizes the
	 * false positive probability is n * k / ln(2) where n is the number of
	 * expected entries in the bloom filter and k is the number of hash
	 * functions. We use 7 / 5 to approximate 1 / ln(2).
	 *
	 * We round this up to the nearest power of two to enable more efficient
	 * hashing using bitmasks. The bitmask will be the bit array size - 1.
	 *
	 * If this overflows a u32, the bit array size will have 2^32 (4
	 * GB) bits.
	 */
	if (check_mul_overflow(attr->max_entries, nr_hash_funcs, &nr_bits) ||
	    check_mul_overflow(nr_bits / 5, (u32)7, &nr_bits) ||
	    nr_bits > (1UL << 31)) {
		/* The bit array size is 2^32 bits but to avoid overflowing the
		 * u32, we use U32_MAX, which will round up to the equivalent
		 * number of bytes
		 */
		bitset_bytes = BITS_TO_BYTES(U32_MAX);
		bitset_mask = U32_MAX;
	} else {
		if (nr_bits <= BITS_PER_LONG)
			nr_bits = BITS_PER_LONG;
		else
			nr_bits = roundup_pow_of_two(nr_bits);
		bitset_bytes = BITS_TO_BYTES(nr_bits);
		bitset_mask = nr_bits - 1;
	}

	bitset_bytes = roundup(bitset_bytes, sizeof(unsigned long));
	bloom = bpf_map_area_alloc(sizeof(*bloom) + bitset_bytes, numa_node);

	if (!bloom)
		return ERR_PTR(-ENOMEM);

	bpf_map_init_from_attr(&bloom->map, attr);

	bloom->nr_hash_funcs = nr_hash_funcs;
	bloom->bitset_mask = bitset_mask;

	/* Check whether the value size is u32-aligned */
	if ((attr->value_size & (sizeof(u32) - 1)) == 0)
		bloom->aligned_u32_count =
			attr->value_size / sizeof(u32);

	if (!(attr->map_flags & BPF_F_ZERO_SEED))
		bloom->hash_seed = get_random_int();

	return &bloom->map;
}

static void bloom_map_free(struct bpf_map *map)
{
	struct bpf_bloom_filter *bloom =
		container_of(map, struct bpf_bloom_filter, map);

	bpf_map_area_free(bloom);
}

static void *bloom_map_lookup_elem(struct bpf_map *map, void *key)
{
	/* The eBPF program should use map_peek_elem instead */
	return ERR_PTR(-EINVAL);
}

static int bloom_map_update_elem(struct bpf_map *map, void *key,
				 void *value, u64 flags)
{
	/* The eBPF program should use map_push_elem instead */
	return -EINVAL;
}

static int bloom_map_check_btf(const struct bpf_map *map,
			       const struct btf *btf,
			       const struct btf_type *key_type,
			       const struct btf_type *value_type)
{
	/* Bloom filter maps are keyless */
	return btf_type_is_void(key_type) ? 0 : -EINVAL;
}

static int bpf_bloom_map_btf_id;
const struct bpf_map_ops bloom_filter_map_ops = {
	.map_meta_equal = bpf_map_meta_equal,
	.map_alloc = bloom_map_alloc,
	.map_free = bloom_map_free,
	.map_get_next_key = bloom_map_get_next_key,
	.map_push_elem = bloom_map_push_elem,
	.map_peek_elem = bloom_map_peek_elem,
	.map_pop_elem = bloom_map_pop_elem,
	.map_lookup_elem = bloom_map_lookup_elem,
	.map_update_elem = bloom_map_update_elem,
	.map_delete_elem = bloom_map_delete_elem,
	.map_check_btf = bloom_map_check_btf,
	.map_btf_name = "bpf_bloom_filter",
	.map_btf_id = &bpf_bloom_map_btf_id,
};