kernel/bpf/stackmap.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Copyright (c) 2016 Facebook
   3  */
   4 #include <linux/bpf.h>
   5 #include <linux/jhash.h>
   6 #include <linux/filter.h>
   7 #include <linux/kernel.h>
   8 #include <linux/stacktrace.h>
   9 #include <linux/perf_event.h>
  10 #include <linux/btf_ids.h>
  11 #include <linux/buildid.h>
  12 #include "percpu_freelist.h"
  13 #include "mmap_unlock_work.h"
  14
  15 #define STACK_CREATE_FLAG_MASK                                  \
  16         (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY |        \
  17          BPF_F_STACK_BUILD_ID)
  18
  19 struct stack_map_bucket {
  20         struct pcpu_freelist_node fnode;
  21         u32 hash;
  22         u32 nr;
  23         u64 data[];
  24 };
  25
  26 struct bpf_stack_map {
  27         struct bpf_map map;
  28         void *elems;
  29         struct pcpu_freelist freelist;
  30         u32 n_buckets;
  31         struct stack_map_bucket *buckets[];
  32 };
  33
  34 static inline bool stack_map_use_build_id(struct bpf_map *map)
  35 {
  36         return (map->map_flags & BPF_F_STACK_BUILD_ID);
  37 }
  38
  39 static inline int stack_map_data_size(struct bpf_map *map)
  40 {
  41         return stack_map_use_build_id(map) ?
  42                 sizeof(struct bpf_stack_build_id) : sizeof(u64);
  43 }
  44
  45 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
  46 {
  47         u64 elem_size = sizeof(struct stack_map_bucket) +
  48                         (u64)smap->map.value_size;
  49         int err;
  50
  51         smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
  52                                          smap->map.numa_node);
  53         if (!smap->elems)
  54                 return -ENOMEM;
  55
  56         err = pcpu_freelist_init(&smap->freelist);
  57         if (err)
  58                 goto free_elems;
  59
  60         pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
  61                                smap->map.max_entries);
  62         return 0;
  63
  64 free_elems:
  65         bpf_map_area_free(smap->elems);
  66         return err;
  67 }
  68
  69 /* Called from syscall */
  70 static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
  71 {
  72         u32 value_size = attr->value_size;
  73         struct bpf_stack_map *smap;
  74         u64 cost, n_buckets;
  75         int err;
  76
  77         if (attr->map_flags & ~STACK_CREATE_FLAG_MASK)
  78                 return ERR_PTR(-EINVAL);
  79
  80         /* check sanity of attributes */
  81         if (attr->max_entries == 0 || attr->key_size != 4 ||
  82             value_size < 8 || value_size % 8)
  83                 return ERR_PTR(-EINVAL);
  84
  85         BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64));
  86         if (attr->map_flags & BPF_F_STACK_BUILD_ID) {
  87                 if (value_size % sizeof(struct bpf_stack_build_id) ||
  88                     value_size / sizeof(struct bpf_stack_build_id)
  89                     > sysctl_perf_event_max_stack)
  90                         return ERR_PTR(-EINVAL);
  91         } else if (value_size / 8 > sysctl_perf_event_max_stack)
  92                 return ERR_PTR(-EINVAL);
  93
  94         /* hash table size must be power of 2 */
  95         n_buckets = roundup_pow_of_two(attr->max_entries);
  96         if (!n_buckets)
  97                 return ERR_PTR(-E2BIG);
  98
  99         cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
 100         smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
 101         if (!smap)
 102                 return ERR_PTR(-ENOMEM);
 103
 104         bpf_map_init_from_attr(&smap->map, attr);
 105         smap->n_buckets = n_buckets;
 106
 107         err = get_callchain_buffers(sysctl_perf_event_max_stack);
 108         if (err)
 109                 goto free_smap;
 110
 111         err = prealloc_elems_and_freelist(smap);
 112         if (err)
 113                 goto put_buffers;
 114
 115         return &smap->map;
 116
 117 put_buffers:
 118         put_callchain_buffers();
 119 free_smap:
 120         bpf_map_area_free(smap);
 121         return ERR_PTR(err);
 122 }
 123
 124 static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 125                                           u64 *ips, u32 trace_nr, bool user)
 126 {
 127         int i;
 128         struct mmap_unlock_irq_work *work = NULL;
 129         bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
 130         struct vm_area_struct *vma, *prev_vma = NULL;
 131         const char *prev_build_id;
 132
 133         /* If the irq_work is in use, fall back to report ips. Same
 134          * fallback is used for kernel stack (!user) on a stackmap with
 135          * build_id.
 136          */
 137         if (!user || !current || !current->mm || irq_work_busy ||
 138             !mmap_read_trylock(current->mm)) {
 139                 /* cannot access current->mm, fall back to ips */
 140                 for (i = 0; i < trace_nr; i++) {
 141                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 142                         id_offs[i].ip = ips[i];
 143                         memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
 144                 }
 145                 return;
 146         }
 147
 148         for (i = 0; i < trace_nr; i++) {
 149                 if (range_in_vma(prev_vma, ips[i], ips[i])) {
 150                         vma = prev_vma;
 151                         memcpy(id_offs[i].build_id, prev_build_id,
 152                                BUILD_ID_SIZE_MAX);
 153                         goto build_id_valid;
 154                 }
 155                 vma = find_vma(current->mm, ips[i]);
 156                 if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) {
 157                         /* per entry fall back to ips */
 158                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 159                         id_offs[i].ip = ips[i];
 160                         memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
 161                         continue;
 162                 }
 163 build_id_valid:
 164                 id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
 165                         - vma->vm_start;
 166                 id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
 167                 prev_vma = vma;
 168                 prev_build_id = id_offs[i].build_id;
 169         }
 170         bpf_mmap_unlock_mm(work, current->mm);
 171 }
 172
 173 static struct perf_callchain_entry *
 174 get_callchain_entry_for_task(struct task_struct *task, u32 max_depth)
 175 {
 176 #ifdef CONFIG_STACKTRACE
 177         struct perf_callchain_entry *entry;
 178         int rctx;
 179
 180         entry = get_callchain_entry(&rctx);
 181
 182         if (!entry)
 183                 return NULL;
 184
 185         entry->nr = stack_trace_save_tsk(task, (unsigned long *)entry->ip,
 186                                          max_depth, 0);
 187
 188         /* stack_trace_save_tsk() works on unsigned long array, while
 189          * perf_callchain_entry uses u64 array. For 32-bit systems, it is
 190          * necessary to fix this mismatch.
 191          */
 192         if (__BITS_PER_LONG != 64) {
 193                 unsigned long *from = (unsigned long *) entry->ip;
 194                 u64 *to = entry->ip;
 195                 int i;
 196
 197                 /* copy data from the end to avoid using extra buffer */
 198                 for (i = entry->nr - 1; i >= 0; i--)
 199                         to[i] = (u64)(from[i]);
 200         }
 201
 202         put_callchain_entry(rctx);
 203
 204         return entry;
 205 #else /* CONFIG_STACKTRACE */
 206         return NULL;
 207 #endif
 208 }
 209
 210 static long __bpf_get_stackid(struct bpf_map *map,
 211                               struct perf_callchain_entry *trace, u64 flags)
 212 {
 213         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 214         struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
 215         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 216         u32 hash, id, trace_nr, trace_len;
 217         bool user = flags & BPF_F_USER_STACK;
 218         u64 *ips;
 219         bool hash_matches;
 220
 221         if (trace->nr <= skip)
 222                 /* skipping more than usable stack trace */
 223                 return -EFAULT;
 224
 225         trace_nr = trace->nr - skip;
 226         trace_len = trace_nr * sizeof(u64);
 227         ips = trace->ip + skip;
 228         hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
 229         id = hash & (smap->n_buckets - 1);
 230         bucket = READ_ONCE(smap->buckets[id]);
 231
 232         hash_matches = bucket && bucket->hash == hash;
 233         /* fast cmp */
 234         if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
 235                 return id;
 236
 237         if (stack_map_use_build_id(map)) {
 238                 /* for build_id+offset, pop a bucket before slow cmp */
 239                 new_bucket = (struct stack_map_bucket *)
 240                         pcpu_freelist_pop(&smap->freelist);
 241                 if (unlikely(!new_bucket))
 242                         return -ENOMEM;
 243                 new_bucket->nr = trace_nr;
 244                 stack_map_get_build_id_offset(
 245                         (struct bpf_stack_build_id *)new_bucket->data,
 246                         ips, trace_nr, user);
 247                 trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
 248                 if (hash_matches && bucket->nr == trace_nr &&
 249                     memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
 250                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 251                         return id;
 252                 }
 253                 if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
 254                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 255                         return -EEXIST;
 256                 }
 257         } else {
 258                 if (hash_matches && bucket->nr == trace_nr &&
 259                     memcmp(bucket->data, ips, trace_len) == 0)
 260                         return id;
 261                 if (bucket && !(flags & BPF_F_REUSE_STACKID))
 262                         return -EEXIST;
 263
 264                 new_bucket = (struct stack_map_bucket *)
 265                         pcpu_freelist_pop(&smap->freelist);
 266                 if (unlikely(!new_bucket))
 267                         return -ENOMEM;
 268                 memcpy(new_bucket->data, ips, trace_len);
 269         }
 270
 271         new_bucket->hash = hash;
 272         new_bucket->nr = trace_nr;
 273
 274         old_bucket = xchg(&smap->buckets[id], new_bucket);
 275         if (old_bucket)
 276                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 277         return id;
 278 }
 279
 280 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 281            u64, flags)
 282 {
 283         u32 max_depth = map->value_size / stack_map_data_size(map);
 284         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 285         bool user = flags & BPF_F_USER_STACK;
 286         struct perf_callchain_entry *trace;
 287         bool kernel = !user;
 288
 289         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 290                                BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
 291                 return -EINVAL;
 292
 293         max_depth += skip;
 294         if (max_depth > sysctl_perf_event_max_stack)
 295                 max_depth = sysctl_perf_event_max_stack;
 296
 297         trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
 298                                    false, false);
 299
 300         if (unlikely(!trace))
 301                 /* couldn't fetch the stack trace */
 302                 return -EFAULT;
 303
 304         return __bpf_get_stackid(map, trace, flags);
 305 }
 306
 307 const struct bpf_func_proto bpf_get_stackid_proto = {
 308         .func           = bpf_get_stackid,
 309         .gpl_only       = true,
 310         .ret_type       = RET_INTEGER,
 311         .arg1_type      = ARG_PTR_TO_CTX,
 312         .arg2_type      = ARG_CONST_MAP_PTR,
 313         .arg3_type      = ARG_ANYTHING,
 314 };
 315
 316 static __u64 count_kernel_ip(struct perf_callchain_entry *trace)
 317 {
 318         __u64 nr_kernel = 0;
 319
 320         while (nr_kernel < trace->nr) {
 321                 if (trace->ip[nr_kernel] == PERF_CONTEXT_USER)
 322                         break;
 323                 nr_kernel++;
 324         }
 325         return nr_kernel;
 326 }
 327
 328 BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 329            struct bpf_map *, map, u64, flags)
 330 {
 331         struct perf_event *event = ctx->event;
 332         struct perf_callchain_entry *trace;
 333         bool kernel, user;
 334         __u64 nr_kernel;
 335         int ret;
 336
 337         /* perf_sample_data doesn't have callchain, use bpf_get_stackid */
 338         if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
 339                 return bpf_get_stackid((unsigned long)(ctx->regs),
 340                                        (unsigned long) map, flags, 0, 0);
 341
 342         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 343                                BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
 344                 return -EINVAL;
 345
 346         user = flags & BPF_F_USER_STACK;
 347         kernel = !user;
 348
 349         trace = ctx->data->callchain;
 350         if (unlikely(!trace))
 351                 return -EFAULT;
 352
 353         nr_kernel = count_kernel_ip(trace);
 354
 355         if (kernel) {
 356                 __u64 nr = trace->nr;
 357
 358                 trace->nr = nr_kernel;
 359                 ret = __bpf_get_stackid(map, trace, flags);
 360
 361                 /* restore nr */
 362                 trace->nr = nr;
 363         } else { /* user */
 364                 u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
 365
 366                 skip += nr_kernel;
 367                 if (skip > BPF_F_SKIP_FIELD_MASK)
 368                         return -EFAULT;
 369
 370                 flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
 371                 ret = __bpf_get_stackid(map, trace, flags);
 372         }
 373         return ret;
 374 }
 375
 376 const struct bpf_func_proto bpf_get_stackid_proto_pe = {
 377         .func           = bpf_get_stackid_pe,
 378         .gpl_only       = false,
 379         .ret_type       = RET_INTEGER,
 380         .arg1_type      = ARG_PTR_TO_CTX,
 381         .arg2_type      = ARG_CONST_MAP_PTR,
 382         .arg3_type      = ARG_ANYTHING,
 383 };
 384
 385 static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 386                             struct perf_callchain_entry *trace_in,
 387                             void *buf, u32 size, u64 flags)
 388 {
 389         u32 trace_nr, copy_len, elem_size, num_elem, max_depth;
 390         bool user_build_id = flags & BPF_F_USER_BUILD_ID;
 391         bool crosstask = task && task != current;
 392         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 393         bool user = flags & BPF_F_USER_STACK;
 394         struct perf_callchain_entry *trace;
 395         bool kernel = !user;
 396         int err = -EINVAL;
 397         u64 *ips;
 398
 399         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 400                                BPF_F_USER_BUILD_ID)))
 401                 goto clear;
 402         if (kernel && user_build_id)
 403                 goto clear;
 404
 405         elem_size = (user && user_build_id) ? sizeof(struct bpf_stack_build_id)
 406                                             : sizeof(u64);
 407         if (unlikely(size % elem_size))
 408                 goto clear;
 409
 410         /* cannot get valid user stack for task without user_mode regs */
 411         if (task && user && !user_mode(regs))
 412                 goto err_fault;
 413
 414         /* get_perf_callchain does not support crosstask user stack walking
 415          * but returns an empty stack instead of NULL.
 416          */
 417         if (crosstask && user) {
 418                 err = -EOPNOTSUPP;
 419                 goto clear;
 420         }
 421
 422         num_elem = size / elem_size;
 423         max_depth = num_elem + skip;
 424         if (sysctl_perf_event_max_stack < max_depth)
 425                 max_depth = sysctl_perf_event_max_stack;
 426
 427         if (trace_in)
 428                 trace = trace_in;
 429         else if (kernel && task)
 430                 trace = get_callchain_entry_for_task(task, max_depth);
 431         else
 432                 trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
 433                                            crosstask, false);
 434         if (unlikely(!trace))
 435                 goto err_fault;
 436
 437         if (trace->nr < skip)
 438                 goto err_fault;
 439
 440         trace_nr = trace->nr - skip;
 441         trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
 442         copy_len = trace_nr * elem_size;
 443
 444         ips = trace->ip + skip;
 445         if (user && user_build_id)
 446                 stack_map_get_build_id_offset(buf, ips, trace_nr, user);
 447         else
 448                 memcpy(buf, ips, copy_len);
 449
 450         if (size > copy_len)
 451                 memset(buf + copy_len, 0, size - copy_len);
 452         return copy_len;
 453
 454 err_fault:
 455         err = -EFAULT;
 456 clear:
 457         memset(buf, 0, size);
 458         return err;
 459 }
 460
 461 BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
 462            u64, flags)
 463 {
 464         return __bpf_get_stack(regs, NULL, NULL, buf, size, flags);
 465 }
 466
 467 const struct bpf_func_proto bpf_get_stack_proto = {
 468         .func           = bpf_get_stack,
 469         .gpl_only       = true,
 470         .ret_type       = RET_INTEGER,
 471         .arg1_type      = ARG_PTR_TO_CTX,
 472         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
 473         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 474         .arg4_type      = ARG_ANYTHING,
 475 };
 476
 477 BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
 478            u32, size, u64, flags)
 479 {
 480         struct pt_regs *regs;
 481         long res = -EINVAL;
 482
 483         if (!try_get_task_stack(task))
 484                 return -EFAULT;
 485
 486         regs = task_pt_regs(task);
 487         if (regs)
 488                 res = __bpf_get_stack(regs, task, NULL, buf, size, flags);
 489         put_task_stack(task);
 490
 491         return res;
 492 }
 493
 494 const struct bpf_func_proto bpf_get_task_stack_proto = {
 495         .func           = bpf_get_task_stack,
 496         .gpl_only       = false,
 497         .ret_type       = RET_INTEGER,
 498         .arg1_type      = ARG_PTR_TO_BTF_ID,
 499         .arg1_btf_id    = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 500         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
 501         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 502         .arg4_type      = ARG_ANYTHING,
 503 };
 504
 505 BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
 506            void *, buf, u32, size, u64, flags)
 507 {
 508         struct pt_regs *regs = (struct pt_regs *)(ctx->regs);
 509         struct perf_event *event = ctx->event;
 510         struct perf_callchain_entry *trace;
 511         bool kernel, user;
 512         int err = -EINVAL;
 513         __u64 nr_kernel;
 514
 515         if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
 516                 return __bpf_get_stack(regs, NULL, NULL, buf, size, flags);
 517
 518         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 519                                BPF_F_USER_BUILD_ID)))
 520                 goto clear;
 521
 522         user = flags & BPF_F_USER_STACK;
 523         kernel = !user;
 524
 525         err = -EFAULT;
 526         trace = ctx->data->callchain;
 527         if (unlikely(!trace))
 528                 goto clear;
 529
 530         nr_kernel = count_kernel_ip(trace);
 531
 532         if (kernel) {
 533                 __u64 nr = trace->nr;
 534
 535                 trace->nr = nr_kernel;
 536                 err = __bpf_get_stack(regs, NULL, trace, buf, size, flags);
 537
 538                 /* restore nr */
 539                 trace->nr = nr;
 540         } else { /* user */
 541                 u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
 542
 543                 skip += nr_kernel;
 544                 if (skip > BPF_F_SKIP_FIELD_MASK)
 545                         goto clear;
 546
 547                 flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
 548                 err = __bpf_get_stack(regs, NULL, trace, buf, size, flags);
 549         }
 550         return err;
 551
 552 clear:
 553         memset(buf, 0, size);
 554         return err;
 555
 556 }
 557
 558 const struct bpf_func_proto bpf_get_stack_proto_pe = {
 559         .func           = bpf_get_stack_pe,
 560         .gpl_only       = true,
 561         .ret_type       = RET_INTEGER,
 562         .arg1_type      = ARG_PTR_TO_CTX,
 563         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
 564         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 565         .arg4_type      = ARG_ANYTHING,
 566 };
 567
 568 /* Called from eBPF program */
 569 static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
 570 {
 571         return ERR_PTR(-EOPNOTSUPP);
 572 }
 573
 574 /* Called from syscall */
 575 int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 576 {
 577         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 578         struct stack_map_bucket *bucket, *old_bucket;
 579         u32 id = *(u32 *)key, trace_len;
 580
 581         if (unlikely(id >= smap->n_buckets))
 582                 return -ENOENT;
 583
 584         bucket = xchg(&smap->buckets[id], NULL);
 585         if (!bucket)
 586                 return -ENOENT;
 587
 588         trace_len = bucket->nr * stack_map_data_size(map);
 589         memcpy(value, bucket->data, trace_len);
 590         memset(value + trace_len, 0, map->value_size - trace_len);
 591
 592         old_bucket = xchg(&smap->buckets[id], bucket);
 593         if (old_bucket)
 594                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 595         return 0;
 596 }
 597
 598 static int stack_map_get_next_key(struct bpf_map *map, void *key,
 599                                   void *next_key)
 600 {
 601         struct bpf_stack_map *smap = container_of(map,
 602                                                   struct bpf_stack_map, map);
 603         u32 id;
 604
 605         WARN_ON_ONCE(!rcu_read_lock_held());
 606
 607         if (!key) {
 608                 id = 0;
 609         } else {
 610                 id = *(u32 *)key;
 611                 if (id >= smap->n_buckets || !smap->buckets[id])
 612                         id = 0;
 613                 else
 614                         id++;
 615         }
 616
 617         while (id < smap->n_buckets && !smap->buckets[id])
 618                 id++;
 619
 620         if (id >= smap->n_buckets)
 621                 return -ENOENT;
 622
 623         *(u32 *)next_key = id;
 624         return 0;
 625 }
 626
 627 static long stack_map_update_elem(struct bpf_map *map, void *key, void *value,
 628                                   u64 map_flags)
 629 {
 630         return -EINVAL;
 631 }
 632
 633 /* Called from syscall or from eBPF program */
 634 static long stack_map_delete_elem(struct bpf_map *map, void *key)
 635 {
 636         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 637         struct stack_map_bucket *old_bucket;
 638         u32 id = *(u32 *)key;
 639
 640         if (unlikely(id >= smap->n_buckets))
 641                 return -E2BIG;
 642
 643         old_bucket = xchg(&smap->buckets[id], NULL);
 644         if (old_bucket) {
 645                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 646                 return 0;
 647         } else {
 648                 return -ENOENT;
 649         }
 650 }
 651
 652 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 653 static void stack_map_free(struct bpf_map *map)
 654 {
 655         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 656
 657         bpf_map_area_free(smap->elems);
 658         pcpu_freelist_destroy(&smap->freelist);
 659         bpf_map_area_free(smap);
 660         put_callchain_buffers();
 661 }
 662
 663 static u64 stack_map_mem_usage(const struct bpf_map *map)
 664 {
 665         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 666         u64 value_size = map->value_size;
 667         u64 n_buckets = smap->n_buckets;
 668         u64 enties = map->max_entries;
 669         u64 usage = sizeof(*smap);
 670
 671         usage += n_buckets * sizeof(struct stack_map_bucket *);
 672         usage += enties * (sizeof(struct stack_map_bucket) + value_size);
 673         return usage;
 674 }
 675
 676 BTF_ID_LIST_SINGLE(stack_trace_map_btf_ids, struct, bpf_stack_map)
 677 const struct bpf_map_ops stack_trace_map_ops = {
 678         .map_meta_equal = bpf_map_meta_equal,
 679         .map_alloc = stack_map_alloc,
 680         .map_free = stack_map_free,
 681         .map_get_next_key = stack_map_get_next_key,
 682         .map_lookup_elem = stack_map_lookup_elem,
 683         .map_update_elem = stack_map_update_elem,
 684         .map_delete_elem = stack_map_delete_elem,
 685         .map_check_btf = map_check_no_btf,
 686         .map_mem_usage = stack_map_mem_usage,
 687         .map_btf_id = &stack_trace_map_btf_ids[0],
 688 };