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 <linux/elf.h> 13 #include <linux/pagemap.h> 14 #include <linux/irq_work.h> 15 #include "percpu_freelist.h" 16 17 #define STACK_CREATE_FLAG_MASK \ 18 (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY | \ 19 BPF_F_STACK_BUILD_ID) 20 21 struct stack_map_bucket { 22 struct pcpu_freelist_node fnode; 23 u32 hash; 24 u32 nr; 25 u64 data[]; 26 }; 27 28 struct bpf_stack_map { 29 struct bpf_map map; 30 void *elems; 31 struct pcpu_freelist freelist; 32 u32 n_buckets; 33 struct stack_map_bucket *buckets[]; 34 }; 35 36 /* irq_work to run up_read() for build_id lookup in nmi context */ 37 struct stack_map_irq_work { 38 struct irq_work irq_work; 39 struct rw_semaphore *sem; 40 }; 41 42 static void do_up_read(struct irq_work *entry) 43 { 44 struct stack_map_irq_work *work; 45 46 work = container_of(entry, struct stack_map_irq_work, irq_work); 47 up_read(work->sem); 48 work->sem = NULL; 49 } 50 51 static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work); 52 53 static inline bool stack_map_use_build_id(struct bpf_map *map) 54 { 55 return (map->map_flags & BPF_F_STACK_BUILD_ID); 56 } 57 58 static inline int stack_map_data_size(struct bpf_map *map) 59 { 60 return stack_map_use_build_id(map) ? 61 sizeof(struct bpf_stack_build_id) : sizeof(u64); 62 } 63 64 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap) 65 { 66 u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size; 67 int err; 68 69 smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries, 70 smap->map.numa_node); 71 if (!smap->elems) 72 return -ENOMEM; 73 74 err = pcpu_freelist_init(&smap->freelist); 75 if (err) 76 goto free_elems; 77 78 pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size, 79 smap->map.max_entries); 80 return 0; 81 82 free_elems: 83 bpf_map_area_free(smap->elems); 84 return err; 85 } 86 87 /* Called from syscall */ 88 static struct bpf_map *stack_map_alloc(union bpf_attr *attr) 89 { 90 u32 value_size = attr->value_size; 91 struct bpf_stack_map *smap; 92 u64 cost, n_buckets; 93 int err; 94 95 if (!capable(CAP_SYS_ADMIN)) 96 return ERR_PTR(-EPERM); 97 98 if (attr->map_flags & ~STACK_CREATE_FLAG_MASK) 99 return ERR_PTR(-EINVAL); 100 101 /* check sanity of attributes */ 102 if (attr->max_entries == 0 || attr->key_size != 4 || 103 value_size < 8 || value_size % 8) 104 return ERR_PTR(-EINVAL); 105 106 BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64)); 107 if (attr->map_flags & BPF_F_STACK_BUILD_ID) { 108 if (value_size % sizeof(struct bpf_stack_build_id) || 109 value_size / sizeof(struct bpf_stack_build_id) 110 > sysctl_perf_event_max_stack) 111 return ERR_PTR(-EINVAL); 112 } else if (value_size / 8 > sysctl_perf_event_max_stack) 113 return ERR_PTR(-EINVAL); 114 115 /* hash table size must be power of 2 */ 116 n_buckets = roundup_pow_of_two(attr->max_entries); 117 118 cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap); 119 if (cost >= U32_MAX - PAGE_SIZE) 120 return ERR_PTR(-E2BIG); 121 122 smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr)); 123 if (!smap) 124 return ERR_PTR(-ENOMEM); 125 126 err = -E2BIG; 127 cost += n_buckets * (value_size + sizeof(struct stack_map_bucket)); 128 if (cost >= U32_MAX - PAGE_SIZE) 129 goto free_smap; 130 131 bpf_map_init_from_attr(&smap->map, attr); 132 smap->map.value_size = value_size; 133 smap->n_buckets = n_buckets; 134 smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT; 135 136 err = bpf_map_precharge_memlock(smap->map.pages); 137 if (err) 138 goto free_smap; 139 140 err = get_callchain_buffers(sysctl_perf_event_max_stack); 141 if (err) 142 goto free_smap; 143 144 err = prealloc_elems_and_freelist(smap); 145 if (err) 146 goto put_buffers; 147 148 return &smap->map; 149 150 put_buffers: 151 put_callchain_buffers(); 152 free_smap: 153 bpf_map_area_free(smap); 154 return ERR_PTR(err); 155 } 156 157 #define BPF_BUILD_ID 3 158 /* 159 * Parse build id from the note segment. This logic can be shared between 160 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are 161 * identical. 162 */ 163 static inline int stack_map_parse_build_id(void *page_addr, 164 unsigned char *build_id, 165 void *note_start, 166 Elf32_Word note_size) 167 { 168 Elf32_Word note_offs = 0, new_offs; 169 170 /* check for overflow */ 171 if (note_start < page_addr || note_start + note_size < note_start) 172 return -EINVAL; 173 174 /* only supports note that fits in the first page */ 175 if (note_start + note_size > page_addr + PAGE_SIZE) 176 return -EINVAL; 177 178 while (note_offs + sizeof(Elf32_Nhdr) < note_size) { 179 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs); 180 181 if (nhdr->n_type == BPF_BUILD_ID && 182 nhdr->n_namesz == sizeof("GNU") && 183 nhdr->n_descsz == BPF_BUILD_ID_SIZE) { 184 memcpy(build_id, 185 note_start + note_offs + 186 ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr), 187 BPF_BUILD_ID_SIZE); 188 return 0; 189 } 190 new_offs = note_offs + sizeof(Elf32_Nhdr) + 191 ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4); 192 if (new_offs <= note_offs) /* overflow */ 193 break; 194 note_offs = new_offs; 195 } 196 return -EINVAL; 197 } 198 199 /* Parse build ID from 32-bit ELF */ 200 static int stack_map_get_build_id_32(void *page_addr, 201 unsigned char *build_id) 202 { 203 Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr; 204 Elf32_Phdr *phdr; 205 int i; 206 207 /* only supports phdr that fits in one page */ 208 if (ehdr->e_phnum > 209 (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr)) 210 return -EINVAL; 211 212 phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr)); 213 214 for (i = 0; i < ehdr->e_phnum; ++i) 215 if (phdr[i].p_type == PT_NOTE) 216 return stack_map_parse_build_id(page_addr, build_id, 217 page_addr + phdr[i].p_offset, 218 phdr[i].p_filesz); 219 return -EINVAL; 220 } 221 222 /* Parse build ID from 64-bit ELF */ 223 static int stack_map_get_build_id_64(void *page_addr, 224 unsigned char *build_id) 225 { 226 Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr; 227 Elf64_Phdr *phdr; 228 int i; 229 230 /* only supports phdr that fits in one page */ 231 if (ehdr->e_phnum > 232 (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr)) 233 return -EINVAL; 234 235 phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr)); 236 237 for (i = 0; i < ehdr->e_phnum; ++i) 238 if (phdr[i].p_type == PT_NOTE) 239 return stack_map_parse_build_id(page_addr, build_id, 240 page_addr + phdr[i].p_offset, 241 phdr[i].p_filesz); 242 return -EINVAL; 243 } 244 245 /* Parse build ID of ELF file mapped to vma */ 246 static int stack_map_get_build_id(struct vm_area_struct *vma, 247 unsigned char *build_id) 248 { 249 Elf32_Ehdr *ehdr; 250 struct page *page; 251 void *page_addr; 252 int ret; 253 254 /* only works for page backed storage */ 255 if (!vma->vm_file) 256 return -EINVAL; 257 258 page = find_get_page(vma->vm_file->f_mapping, 0); 259 if (!page) 260 return -EFAULT; /* page not mapped */ 261 262 ret = -EINVAL; 263 page_addr = page_address(page); 264 ehdr = (Elf32_Ehdr *)page_addr; 265 266 /* compare magic x7f "ELF" */ 267 if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) 268 goto out; 269 270 /* only support executable file and shared object file */ 271 if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) 272 goto out; 273 274 if (ehdr->e_ident[EI_CLASS] == ELFCLASS32) 275 ret = stack_map_get_build_id_32(page_addr, build_id); 276 else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64) 277 ret = stack_map_get_build_id_64(page_addr, build_id); 278 out: 279 put_page(page); 280 return ret; 281 } 282 283 static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, 284 u64 *ips, u32 trace_nr, bool user) 285 { 286 int i; 287 struct vm_area_struct *vma; 288 bool irq_work_busy = false; 289 struct stack_map_irq_work *work = NULL; 290 291 if (in_nmi()) { 292 work = this_cpu_ptr(&up_read_work); 293 if (work->irq_work.flags & IRQ_WORK_BUSY) 294 /* cannot queue more up_read, fallback */ 295 irq_work_busy = true; 296 } 297 298 /* 299 * We cannot do up_read() in nmi context. To do build_id lookup 300 * in nmi context, we need to run up_read() in irq_work. We use 301 * a percpu variable to do the irq_work. If the irq_work is 302 * already used by another lookup, we fall back to report ips. 303 * 304 * Same fallback is used for kernel stack (!user) on a stackmap 305 * with build_id. 306 */ 307 if (!user || !current || !current->mm || irq_work_busy || 308 down_read_trylock(¤t->mm->mmap_sem) == 0) { 309 /* cannot access current->mm, fall back to ips */ 310 for (i = 0; i < trace_nr; i++) { 311 id_offs[i].status = BPF_STACK_BUILD_ID_IP; 312 id_offs[i].ip = ips[i]; 313 } 314 return; 315 } 316 317 for (i = 0; i < trace_nr; i++) { 318 vma = find_vma(current->mm, ips[i]); 319 if (!vma || stack_map_get_build_id(vma, id_offs[i].build_id)) { 320 /* per entry fall back to ips */ 321 id_offs[i].status = BPF_STACK_BUILD_ID_IP; 322 id_offs[i].ip = ips[i]; 323 continue; 324 } 325 id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i] 326 - vma->vm_start; 327 id_offs[i].status = BPF_STACK_BUILD_ID_VALID; 328 } 329 330 if (!work) { 331 up_read(¤t->mm->mmap_sem); 332 } else { 333 work->sem = ¤t->mm->mmap_sem; 334 irq_work_queue(&work->irq_work); 335 } 336 } 337 338 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, 339 u64, flags) 340 { 341 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 342 struct perf_callchain_entry *trace; 343 struct stack_map_bucket *bucket, *new_bucket, *old_bucket; 344 u32 max_depth = map->value_size / stack_map_data_size(map); 345 /* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */ 346 u32 init_nr = sysctl_perf_event_max_stack - max_depth; 347 u32 skip = flags & BPF_F_SKIP_FIELD_MASK; 348 u32 hash, id, trace_nr, trace_len; 349 bool user = flags & BPF_F_USER_STACK; 350 bool kernel = !user; 351 u64 *ips; 352 bool hash_matches; 353 354 if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | 355 BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) 356 return -EINVAL; 357 358 trace = get_perf_callchain(regs, init_nr, kernel, user, 359 sysctl_perf_event_max_stack, false, false); 360 361 if (unlikely(!trace)) 362 /* couldn't fetch the stack trace */ 363 return -EFAULT; 364 365 /* get_perf_callchain() guarantees that trace->nr >= init_nr 366 * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth 367 */ 368 trace_nr = trace->nr - init_nr; 369 370 if (trace_nr <= skip) 371 /* skipping more than usable stack trace */ 372 return -EFAULT; 373 374 trace_nr -= skip; 375 trace_len = trace_nr * sizeof(u64); 376 ips = trace->ip + skip + init_nr; 377 hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); 378 id = hash & (smap->n_buckets - 1); 379 bucket = READ_ONCE(smap->buckets[id]); 380 381 hash_matches = bucket && bucket->hash == hash; 382 /* fast cmp */ 383 if (hash_matches && flags & BPF_F_FAST_STACK_CMP) 384 return id; 385 386 if (stack_map_use_build_id(map)) { 387 /* for build_id+offset, pop a bucket before slow cmp */ 388 new_bucket = (struct stack_map_bucket *) 389 pcpu_freelist_pop(&smap->freelist); 390 if (unlikely(!new_bucket)) 391 return -ENOMEM; 392 new_bucket->nr = trace_nr; 393 stack_map_get_build_id_offset( 394 (struct bpf_stack_build_id *)new_bucket->data, 395 ips, trace_nr, user); 396 trace_len = trace_nr * sizeof(struct bpf_stack_build_id); 397 if (hash_matches && bucket->nr == trace_nr && 398 memcmp(bucket->data, new_bucket->data, trace_len) == 0) { 399 pcpu_freelist_push(&smap->freelist, &new_bucket->fnode); 400 return id; 401 } 402 if (bucket && !(flags & BPF_F_REUSE_STACKID)) { 403 pcpu_freelist_push(&smap->freelist, &new_bucket->fnode); 404 return -EEXIST; 405 } 406 } else { 407 if (hash_matches && bucket->nr == trace_nr && 408 memcmp(bucket->data, ips, trace_len) == 0) 409 return id; 410 if (bucket && !(flags & BPF_F_REUSE_STACKID)) 411 return -EEXIST; 412 413 new_bucket = (struct stack_map_bucket *) 414 pcpu_freelist_pop(&smap->freelist); 415 if (unlikely(!new_bucket)) 416 return -ENOMEM; 417 memcpy(new_bucket->data, ips, trace_len); 418 } 419 420 new_bucket->hash = hash; 421 new_bucket->nr = trace_nr; 422 423 old_bucket = xchg(&smap->buckets[id], new_bucket); 424 if (old_bucket) 425 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 426 return id; 427 } 428 429 const struct bpf_func_proto bpf_get_stackid_proto = { 430 .func = bpf_get_stackid, 431 .gpl_only = true, 432 .ret_type = RET_INTEGER, 433 .arg1_type = ARG_PTR_TO_CTX, 434 .arg2_type = ARG_CONST_MAP_PTR, 435 .arg3_type = ARG_ANYTHING, 436 }; 437 438 BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size, 439 u64, flags) 440 { 441 u32 init_nr, trace_nr, copy_len, elem_size, num_elem; 442 bool user_build_id = flags & BPF_F_USER_BUILD_ID; 443 u32 skip = flags & BPF_F_SKIP_FIELD_MASK; 444 bool user = flags & BPF_F_USER_STACK; 445 struct perf_callchain_entry *trace; 446 bool kernel = !user; 447 int err = -EINVAL; 448 u64 *ips; 449 450 if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | 451 BPF_F_USER_BUILD_ID))) 452 goto clear; 453 if (kernel && user_build_id) 454 goto clear; 455 456 elem_size = (user && user_build_id) ? sizeof(struct bpf_stack_build_id) 457 : sizeof(u64); 458 if (unlikely(size % elem_size)) 459 goto clear; 460 461 num_elem = size / elem_size; 462 if (sysctl_perf_event_max_stack < num_elem) 463 init_nr = 0; 464 else 465 init_nr = sysctl_perf_event_max_stack - num_elem; 466 trace = get_perf_callchain(regs, init_nr, kernel, user, 467 sysctl_perf_event_max_stack, false, false); 468 if (unlikely(!trace)) 469 goto err_fault; 470 471 trace_nr = trace->nr - init_nr; 472 if (trace_nr < skip) 473 goto err_fault; 474 475 trace_nr -= skip; 476 trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem; 477 copy_len = trace_nr * elem_size; 478 ips = trace->ip + skip + init_nr; 479 if (user && user_build_id) 480 stack_map_get_build_id_offset(buf, ips, trace_nr, user); 481 else 482 memcpy(buf, ips, copy_len); 483 484 if (size > copy_len) 485 memset(buf + copy_len, 0, size - copy_len); 486 return copy_len; 487 488 err_fault: 489 err = -EFAULT; 490 clear: 491 memset(buf, 0, size); 492 return err; 493 } 494 495 const struct bpf_func_proto bpf_get_stack_proto = { 496 .func = bpf_get_stack, 497 .gpl_only = true, 498 .ret_type = RET_INTEGER, 499 .arg1_type = ARG_PTR_TO_CTX, 500 .arg2_type = ARG_PTR_TO_UNINIT_MEM, 501 .arg3_type = ARG_CONST_SIZE_OR_ZERO, 502 .arg4_type = ARG_ANYTHING, 503 }; 504 505 /* Called from eBPF program */ 506 static void *stack_map_lookup_elem(struct bpf_map *map, void *key) 507 { 508 return NULL; 509 } 510 511 /* Called from syscall */ 512 int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value) 513 { 514 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 515 struct stack_map_bucket *bucket, *old_bucket; 516 u32 id = *(u32 *)key, trace_len; 517 518 if (unlikely(id >= smap->n_buckets)) 519 return -ENOENT; 520 521 bucket = xchg(&smap->buckets[id], NULL); 522 if (!bucket) 523 return -ENOENT; 524 525 trace_len = bucket->nr * stack_map_data_size(map); 526 memcpy(value, bucket->data, trace_len); 527 memset(value + trace_len, 0, map->value_size - trace_len); 528 529 old_bucket = xchg(&smap->buckets[id], bucket); 530 if (old_bucket) 531 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 532 return 0; 533 } 534 535 static int stack_map_get_next_key(struct bpf_map *map, void *key, 536 void *next_key) 537 { 538 struct bpf_stack_map *smap = container_of(map, 539 struct bpf_stack_map, map); 540 u32 id; 541 542 WARN_ON_ONCE(!rcu_read_lock_held()); 543 544 if (!key) { 545 id = 0; 546 } else { 547 id = *(u32 *)key; 548 if (id >= smap->n_buckets || !smap->buckets[id]) 549 id = 0; 550 else 551 id++; 552 } 553 554 while (id < smap->n_buckets && !smap->buckets[id]) 555 id++; 556 557 if (id >= smap->n_buckets) 558 return -ENOENT; 559 560 *(u32 *)next_key = id; 561 return 0; 562 } 563 564 static int stack_map_update_elem(struct bpf_map *map, void *key, void *value, 565 u64 map_flags) 566 { 567 return -EINVAL; 568 } 569 570 /* Called from syscall or from eBPF program */ 571 static int stack_map_delete_elem(struct bpf_map *map, void *key) 572 { 573 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 574 struct stack_map_bucket *old_bucket; 575 u32 id = *(u32 *)key; 576 577 if (unlikely(id >= smap->n_buckets)) 578 return -E2BIG; 579 580 old_bucket = xchg(&smap->buckets[id], NULL); 581 if (old_bucket) { 582 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode); 583 return 0; 584 } else { 585 return -ENOENT; 586 } 587 } 588 589 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */ 590 static void stack_map_free(struct bpf_map *map) 591 { 592 struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); 593 594 /* wait for bpf programs to complete before freeing stack map */ 595 synchronize_rcu(); 596 597 bpf_map_area_free(smap->elems); 598 pcpu_freelist_destroy(&smap->freelist); 599 bpf_map_area_free(smap); 600 put_callchain_buffers(); 601 } 602 603 const struct bpf_map_ops stack_map_ops = { 604 .map_alloc = stack_map_alloc, 605 .map_free = stack_map_free, 606 .map_get_next_key = stack_map_get_next_key, 607 .map_lookup_elem = stack_map_lookup_elem, 608 .map_update_elem = stack_map_update_elem, 609 .map_delete_elem = stack_map_delete_elem, 610 }; 611 612 static int __init stack_map_init(void) 613 { 614 int cpu; 615 struct stack_map_irq_work *work; 616 617 for_each_possible_cpu(cpu) { 618 work = per_cpu_ptr(&up_read_work, cpu); 619 init_irq_work(&work->irq_work, do_up_read); 620 } 621 return 0; 622 } 623 subsys_initcall(stack_map_init); 624