1 /* Copyright (c) 2016 Facebook 2 * 3 * This program is free software; you can redistribute it and/or 4 * modify it under the terms of version 2 of the GNU General Public 5 * License as published by the Free Software Foundation. 6 */ 7 #include <linux/bpf.h> 8 #include <linux/jhash.h> 9 #include <linux/filter.h> 10 #include <linux/stacktrace.h> 11 #include <linux/perf_event.h> 12 #include "percpu_freelist.h" 13 14 struct stack_map_bucket { 15 struct pcpu_freelist_node fnode; 16 u32 hash; 17 u32 nr; 18 u64 ip[]; 19 }; 20 21 struct bpf_stack_map { 22 struct bpf_map map; 23 void *elems; 24 struct pcpu_freelist freelist; 25 u32 n_buckets; 26 struct stack_map_bucket *buckets[]; 27 }; 28 29 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap) 30 { 31 u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size; 32 int err; 33 34 smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries); 35 if (!smap->elems) 36 return -ENOMEM; 37 38 err = pcpu_freelist_init(&smap->freelist); 39 if (err) 40 goto free_elems; 41 42 pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size, 43 smap->map.max_entries); 44 return 0; 45 46 free_elems: 47 bpf_map_area_free(smap->elems); 48 return err; 49 } 50 51 /* Called from syscall */ 52 static struct bpf_map *stack_map_alloc(union bpf_attr *attr) 53 { 54 u32 value_size = attr->value_size; 55 struct bpf_stack_map *smap; 56 u64 cost, n_buckets; 57 int err; 58 59 if (!capable(CAP_SYS_ADMIN)) 60 return ERR_PTR(-EPERM); 61 62 if (attr->map_flags) 63 return ERR_PTR(-EINVAL); 64 65 /* check sanity of attributes */ 66 if (attr->max_entries == 0 || attr->key_size != 4 || 67 value_size < 8 || value_size % 8 || 68 value_size / 8 > sysctl_perf_event_max_stack) 69 return ERR_PTR(-EINVAL); 70 71 /* hash table size must be power of 2 */ 72 n_buckets = roundup_pow_of_two(attr->max_entries); 73 74 cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap); 75 if (cost >= U32_MAX - PAGE_SIZE) 76 return ERR_PTR(-E2BIG); 77 78 smap = bpf_map_area_alloc(cost); 79 if (!smap) 80 return ERR_PTR(-ENOMEM); 81 82 err = -E2BIG; 83 cost += n_buckets * (value_size + sizeof(struct stack_map_bucket)); 84 if (cost >= U32_MAX - PAGE_SIZE) 85 goto free_smap; 86 87 smap->map.map_type = attr->map_type; 88 smap->map.key_size = attr->key_size; 89 smap->map.value_size = value_size; 90 smap->map.max_entries = attr->max_entries; 91 smap->map.map_flags = attr->map_flags; 92 smap->n_buckets = n_buckets; 93 smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT; 94 95 err = bpf_map_precharge_memlock(smap->map.pages); 96 if (err) 97 goto free_smap; 98 99 err = get_callchain_buffers(sysctl_perf_event_max_stack); 100 if (err) 101 goto free_smap; 102 103 err = prealloc_elems_and_freelist(smap); 104 if (err) 105 goto put_buffers; 106 107 return &smap->map; 108 109 put_buffers: 110 put_callchain_buffers(); 111 free_smap: 112 bpf_map_area_free(smap); 113 return ERR_PTR(err); 114 } 115 116 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, 117 u64, flags) 118 { 119 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 120 struct perf_callchain_entry *trace; 121 struct stack_map_bucket *bucket, *new_bucket, *old_bucket; 122 u32 max_depth = map->value_size / 8; 123 /* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */ 124 u32 init_nr = sysctl_perf_event_max_stack - max_depth; 125 u32 skip = flags & BPF_F_SKIP_FIELD_MASK; 126 u32 hash, id, trace_nr, trace_len; 127 bool user = flags & BPF_F_USER_STACK; 128 bool kernel = !user; 129 u64 *ips; 130 131 if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | 132 BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) 133 return -EINVAL; 134 135 trace = get_perf_callchain(regs, init_nr, kernel, user, 136 sysctl_perf_event_max_stack, false, false); 137 138 if (unlikely(!trace)) 139 /* couldn't fetch the stack trace */ 140 return -EFAULT; 141 142 /* get_perf_callchain() guarantees that trace->nr >= init_nr 143 * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth 144 */ 145 trace_nr = trace->nr - init_nr; 146 147 if (trace_nr <= skip) 148 /* skipping more than usable stack trace */ 149 return -EFAULT; 150 151 trace_nr -= skip; 152 trace_len = trace_nr * sizeof(u64); 153 ips = trace->ip + skip + init_nr; 154 hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); 155 id = hash & (smap->n_buckets - 1); 156 bucket = READ_ONCE(smap->buckets[id]); 157 158 if (bucket && bucket->hash == hash) { 159 if (flags & BPF_F_FAST_STACK_CMP) 160 return id; 161 if (bucket->nr == trace_nr && 162 memcmp(bucket->ip, ips, trace_len) == 0) 163 return id; 164 } 165 166 /* this call stack is not in the map, try to add it */ 167 if (bucket && !(flags & BPF_F_REUSE_STACKID)) 168 return -EEXIST; 169 170 new_bucket = (struct stack_map_bucket *) 171 pcpu_freelist_pop(&smap->freelist); 172 if (unlikely(!new_bucket)) 173 return -ENOMEM; 174 175 memcpy(new_bucket->ip, ips, trace_len); 176 new_bucket->hash = hash; 177 new_bucket->nr = trace_nr; 178 179 old_bucket = xchg(&smap->buckets[id], new_bucket); 180 if (old_bucket) 181 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 182 return id; 183 } 184 185 const struct bpf_func_proto bpf_get_stackid_proto = { 186 .func = bpf_get_stackid, 187 .gpl_only = true, 188 .ret_type = RET_INTEGER, 189 .arg1_type = ARG_PTR_TO_CTX, 190 .arg2_type = ARG_CONST_MAP_PTR, 191 .arg3_type = ARG_ANYTHING, 192 }; 193 194 /* Called from eBPF program */ 195 static void *stack_map_lookup_elem(struct bpf_map *map, void *key) 196 { 197 return NULL; 198 } 199 200 /* Called from syscall */ 201 int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value) 202 { 203 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 204 struct stack_map_bucket *bucket, *old_bucket; 205 u32 id = *(u32 *)key, trace_len; 206 207 if (unlikely(id >= smap->n_buckets)) 208 return -ENOENT; 209 210 bucket = xchg(&smap->buckets[id], NULL); 211 if (!bucket) 212 return -ENOENT; 213 214 trace_len = bucket->nr * sizeof(u64); 215 memcpy(value, bucket->ip, trace_len); 216 memset(value + trace_len, 0, map->value_size - trace_len); 217 218 old_bucket = xchg(&smap->buckets[id], bucket); 219 if (old_bucket) 220 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 221 return 0; 222 } 223 224 static int stack_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 225 { 226 return -EINVAL; 227 } 228 229 static int stack_map_update_elem(struct bpf_map *map, void *key, void *value, 230 u64 map_flags) 231 { 232 return -EINVAL; 233 } 234 235 /* Called from syscall or from eBPF program */ 236 static int stack_map_delete_elem(struct bpf_map *map, void *key) 237 { 238 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 239 struct stack_map_bucket *old_bucket; 240 u32 id = *(u32 *)key; 241 242 if (unlikely(id >= smap->n_buckets)) 243 return -E2BIG; 244 245 old_bucket = xchg(&smap->buckets[id], NULL); 246 if (old_bucket) { 247 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 248 return 0; 249 } else { 250 return -ENOENT; 251 } 252 } 253 254 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */ 255 static void stack_map_free(struct bpf_map *map) 256 { 257 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 258 259 /* wait for bpf programs to complete before freeing stack map */ 260 synchronize_rcu(); 261 262 bpf_map_area_free(smap->elems); 263 pcpu_freelist_destroy(&smap->freelist); 264 bpf_map_area_free(smap); 265 put_callchain_buffers(); 266 } 267 268 const struct bpf_map_ops stack_map_ops = { 269 .map_alloc = stack_map_alloc, 270 .map_free = stack_map_free, 271 .map_get_next_key = stack_map_get_next_key, 272 .map_lookup_elem = stack_map_lookup_elem, 273 .map_update_elem = stack_map_update_elem, 274 .map_delete_elem = stack_map_delete_elem, 275 }; 276