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 15 struct 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 30 static 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 44 static 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 59 static 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 76 static int bloom_map_pop_elem(struct bpf_map *map, void *value) 77 { 78 return -EOPNOTSUPP; 79 } 80 81 static int bloom_map_delete_elem(struct bpf_map *map, void *value) 82 { 83 return -EOPNOTSUPP; 84 } 85 86 static int bloom_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 87 { 88 return -EOPNOTSUPP; 89 } 90 91 static 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 } 165 166 static 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 } 173 174 static 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 } 179 180 static 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 } 186 187 static 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 } 195 196 BTF_ID_LIST_SINGLE(bpf_bloom_map_btf_ids, struct, bpf_bloom_filter) 197 const 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