tools/lib/bpf/relo_core.c

   1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
   2 /* Copyright (c) 2019 Facebook */
   3
   4 #ifdef __KERNEL__
   5 #include <linux/bpf.h>
   6 #include <linux/btf.h>
   7 #include <linux/string.h>
   8 #include <linux/bpf_verifier.h>
   9 #include "relo_core.h"
  10
  11 static const char *btf_kind_str(const struct btf_type *t)
  12 {
  13         return btf_type_str(t);
  14 }
  15
  16 static bool is_ldimm64_insn(struct bpf_insn *insn)
  17 {
  18         return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
  19 }
  20
  21 static const struct btf_type *
  22 skip_mods_and_typedefs(const struct btf *btf, u32 id, u32 *res_id)
  23 {
  24         return btf_type_skip_modifiers(btf, id, res_id);
  25 }
  26
  27 static const char *btf__name_by_offset(const struct btf *btf, u32 offset)
  28 {
  29         return btf_name_by_offset(btf, offset);
  30 }
  31
  32 static s64 btf__resolve_size(const struct btf *btf, u32 type_id)
  33 {
  34         const struct btf_type *t;
  35         int size;
  36
  37         t = btf_type_by_id(btf, type_id);
  38         t = btf_resolve_size(btf, t, &size);
  39         if (IS_ERR(t))
  40                 return PTR_ERR(t);
  41         return size;
  42 }
  43
  44 enum libbpf_print_level {
  45         LIBBPF_WARN,
  46         LIBBPF_INFO,
  47         LIBBPF_DEBUG,
  48 };
  49
  50 #undef pr_warn
  51 #undef pr_info
  52 #undef pr_debug
  53 #define pr_warn(fmt, log, ...)  bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
  54 #define pr_info(fmt, log, ...)  bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
  55 #define pr_debug(fmt, log, ...) bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
  56 #define libbpf_print(level, fmt, ...)   bpf_log((void *)prog_name, fmt, ##__VA_ARGS__)
  57 #else
  58 #include <stdio.h>
  59 #include <string.h>
  60 #include <errno.h>
  61 #include <ctype.h>
  62 #include <linux/err.h>
  63
  64 #include "libbpf.h"
  65 #include "bpf.h"
  66 #include "btf.h"
  67 #include "str_error.h"
  68 #include "libbpf_internal.h"
  69 #endif
  70
  71 static bool is_flex_arr(const struct btf *btf,
  72                         const struct bpf_core_accessor *acc,
  73                         const struct btf_array *arr)
  74 {
  75         const struct btf_type *t;
  76
  77         /* not a flexible array, if not inside a struct or has non-zero size */
  78         if (!acc->name || arr->nelems > 0)
  79                 return false;
  80
  81         /* has to be the last member of enclosing struct */
  82         t = btf_type_by_id(btf, acc->type_id);
  83         return acc->idx == btf_vlen(t) - 1;
  84 }
  85
  86 static const char *core_relo_kind_str(enum bpf_core_relo_kind kind)
  87 {
  88         switch (kind) {
  89         case BPF_CORE_FIELD_BYTE_OFFSET: return "byte_off";
  90         case BPF_CORE_FIELD_BYTE_SIZE: return "byte_sz";
  91         case BPF_CORE_FIELD_EXISTS: return "field_exists";
  92         case BPF_CORE_FIELD_SIGNED: return "signed";
  93         case BPF_CORE_FIELD_LSHIFT_U64: return "lshift_u64";
  94         case BPF_CORE_FIELD_RSHIFT_U64: return "rshift_u64";
  95         case BPF_CORE_TYPE_ID_LOCAL: return "local_type_id";
  96         case BPF_CORE_TYPE_ID_TARGET: return "target_type_id";
  97         case BPF_CORE_TYPE_EXISTS: return "type_exists";
  98         case BPF_CORE_TYPE_SIZE: return "type_size";
  99         case BPF_CORE_ENUMVAL_EXISTS: return "enumval_exists";
 100         case BPF_CORE_ENUMVAL_VALUE: return "enumval_value";
 101         default: return "unknown";
 102         }
 103 }
 104
 105 static bool core_relo_is_field_based(enum bpf_core_relo_kind kind)
 106 {
 107         switch (kind) {
 108         case BPF_CORE_FIELD_BYTE_OFFSET:
 109         case BPF_CORE_FIELD_BYTE_SIZE:
 110         case BPF_CORE_FIELD_EXISTS:
 111         case BPF_CORE_FIELD_SIGNED:
 112         case BPF_CORE_FIELD_LSHIFT_U64:
 113         case BPF_CORE_FIELD_RSHIFT_U64:
 114                 return true;
 115         default:
 116                 return false;
 117         }
 118 }
 119
 120 static bool core_relo_is_type_based(enum bpf_core_relo_kind kind)
 121 {
 122         switch (kind) {
 123         case BPF_CORE_TYPE_ID_LOCAL:
 124         case BPF_CORE_TYPE_ID_TARGET:
 125         case BPF_CORE_TYPE_EXISTS:
 126         case BPF_CORE_TYPE_SIZE:
 127                 return true;
 128         default:
 129                 return false;
 130         }
 131 }
 132
 133 static bool core_relo_is_enumval_based(enum bpf_core_relo_kind kind)
 134 {
 135         switch (kind) {
 136         case BPF_CORE_ENUMVAL_EXISTS:
 137         case BPF_CORE_ENUMVAL_VALUE:
 138                 return true;
 139         default:
 140                 return false;
 141         }
 142 }
 143
 144 int __bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
 145                                 const struct btf *targ_btf, __u32 targ_id, int level)
 146 {
 147         const struct btf_type *local_type, *targ_type;
 148         int depth = 32; /* max recursion depth */
 149
 150         /* caller made sure that names match (ignoring flavor suffix) */
 151         local_type = btf_type_by_id(local_btf, local_id);
 152         targ_type = btf_type_by_id(targ_btf, targ_id);
 153         if (!btf_kind_core_compat(local_type, targ_type))
 154                 return 0;
 155
 156 recur:
 157         depth--;
 158         if (depth < 0)
 159                 return -EINVAL;
 160
 161         local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
 162         targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
 163         if (!local_type || !targ_type)
 164                 return -EINVAL;
 165
 166         if (!btf_kind_core_compat(local_type, targ_type))
 167                 return 0;
 168
 169         switch (btf_kind(local_type)) {
 170         case BTF_KIND_UNKN:
 171         case BTF_KIND_STRUCT:
 172         case BTF_KIND_UNION:
 173         case BTF_KIND_ENUM:
 174         case BTF_KIND_FWD:
 175         case BTF_KIND_ENUM64:
 176                 return 1;
 177         case BTF_KIND_INT:
 178                 /* just reject deprecated bitfield-like integers; all other
 179                  * integers are by default compatible between each other
 180                  */
 181                 return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0;
 182         case BTF_KIND_PTR:
 183                 local_id = local_type->type;
 184                 targ_id = targ_type->type;
 185                 goto recur;
 186         case BTF_KIND_ARRAY:
 187                 local_id = btf_array(local_type)->type;
 188                 targ_id = btf_array(targ_type)->type;
 189                 goto recur;
 190         case BTF_KIND_FUNC_PROTO: {
 191                 struct btf_param *local_p = btf_params(local_type);
 192                 struct btf_param *targ_p = btf_params(targ_type);
 193                 __u16 local_vlen = btf_vlen(local_type);
 194                 __u16 targ_vlen = btf_vlen(targ_type);
 195                 int i, err;
 196
 197                 if (local_vlen != targ_vlen)
 198                         return 0;
 199
 200                 for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
 201                         if (level <= 0)
 202                                 return -EINVAL;
 203
 204                         skip_mods_and_typedefs(local_btf, local_p->type, &local_id);
 205                         skip_mods_and_typedefs(targ_btf, targ_p->type, &targ_id);
 206                         err = __bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id,
 207                                                           level - 1);
 208                         if (err <= 0)
 209                                 return err;
 210                 }
 211
 212                 /* tail recurse for return type check */
 213                 skip_mods_and_typedefs(local_btf, local_type->type, &local_id);
 214                 skip_mods_and_typedefs(targ_btf, targ_type->type, &targ_id);
 215                 goto recur;
 216         }
 217         default:
 218                 pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
 219                         btf_kind_str(local_type), local_id, targ_id);
 220                 return 0;
 221         }
 222 }
 223
 224 /*
 225  * Turn bpf_core_relo into a low- and high-level spec representation,
 226  * validating correctness along the way, as well as calculating resulting
 227  * field bit offset, specified by accessor string. Low-level spec captures
 228  * every single level of nestedness, including traversing anonymous
 229  * struct/union members. High-level one only captures semantically meaningful
 230  * "turning points": named fields and array indicies.
 231  * E.g., for this case:
 232  *
 233  *   struct sample {
 234  *       int __unimportant;
 235  *       struct {
 236  *           int __1;
 237  *           int __2;
 238  *           int a[7];
 239  *       };
 240  *   };
 241  *
 242  *   struct sample *s = ...;
 243  *
 244  *   int x = &s->a[3]; // access string = '0:1:2:3'
 245  *
 246  * Low-level spec has 1:1 mapping with each element of access string (it's
 247  * just a parsed access string representation): [0, 1, 2, 3].
 248  *
 249  * High-level spec will capture only 3 points:
 250  *   - initial zero-index access by pointer (&s->... is the same as &s[0]...);
 251  *   - field 'a' access (corresponds to '2' in low-level spec);
 252  *   - array element #3 access (corresponds to '3' in low-level spec).
 253  *
 254  * Type-based relocations (TYPE_EXISTS/TYPE_SIZE,
 255  * TYPE_ID_LOCAL/TYPE_ID_TARGET) don't capture any field information. Their
 256  * spec and raw_spec are kept empty.
 257  *
 258  * Enum value-based relocations (ENUMVAL_EXISTS/ENUMVAL_VALUE) use access
 259  * string to specify enumerator's value index that need to be relocated.
 260  */
 261 int bpf_core_parse_spec(const char *prog_name, const struct btf *btf,
 262                         const struct bpf_core_relo *relo,
 263                         struct bpf_core_spec *spec)
 264 {
 265         int access_idx, parsed_len, i;
 266         struct bpf_core_accessor *acc;
 267         const struct btf_type *t;
 268         const char *name, *spec_str;
 269         __u32 id, name_off;
 270         __s64 sz;
 271
 272         spec_str = btf__name_by_offset(btf, relo->access_str_off);
 273         if (str_is_empty(spec_str) || *spec_str == ':')
 274                 return -EINVAL;
 275
 276         memset(spec, 0, sizeof(*spec));
 277         spec->btf = btf;
 278         spec->root_type_id = relo->type_id;
 279         spec->relo_kind = relo->kind;
 280
 281         /* type-based relocations don't have a field access string */
 282         if (core_relo_is_type_based(relo->kind)) {
 283                 if (strcmp(spec_str, "0"))
 284                         return -EINVAL;
 285                 return 0;
 286         }
 287
 288         /* parse spec_str="0:1:2:3:4" into array raw_spec=[0, 1, 2, 3, 4] */
 289         while (*spec_str) {
 290                 if (*spec_str == ':')
 291                         ++spec_str;
 292                 if (sscanf(spec_str, "%d%n", &access_idx, &parsed_len) != 1)
 293                         return -EINVAL;
 294                 if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
 295                         return -E2BIG;
 296                 spec_str += parsed_len;
 297                 spec->raw_spec[spec->raw_len++] = access_idx;
 298         }
 299
 300         if (spec->raw_len == 0)
 301                 return -EINVAL;
 302
 303         t = skip_mods_and_typedefs(btf, relo->type_id, &id);
 304         if (!t)
 305                 return -EINVAL;
 306
 307         access_idx = spec->raw_spec[0];
 308         acc = &spec->spec[0];
 309         acc->type_id = id;
 310         acc->idx = access_idx;
 311         spec->len++;
 312
 313         if (core_relo_is_enumval_based(relo->kind)) {
 314                 if (!btf_is_any_enum(t) || spec->raw_len > 1 || access_idx >= btf_vlen(t))
 315                         return -EINVAL;
 316
 317                 /* record enumerator name in a first accessor */
 318                 name_off = btf_is_enum(t) ? btf_enum(t)[access_idx].name_off
 319                                           : btf_enum64(t)[access_idx].name_off;
 320                 acc->name = btf__name_by_offset(btf, name_off);
 321                 return 0;
 322         }
 323
 324         if (!core_relo_is_field_based(relo->kind))
 325                 return -EINVAL;
 326
 327         sz = btf__resolve_size(btf, id);
 328         if (sz < 0)
 329                 return sz;
 330         spec->bit_offset = access_idx * sz * 8;
 331
 332         for (i = 1; i < spec->raw_len; i++) {
 333                 t = skip_mods_and_typedefs(btf, id, &id);
 334                 if (!t)
 335                         return -EINVAL;
 336
 337                 access_idx = spec->raw_spec[i];
 338                 acc = &spec->spec[spec->len];
 339
 340                 if (btf_is_composite(t)) {
 341                         const struct btf_member *m;
 342                         __u32 bit_offset;
 343
 344                         if (access_idx >= btf_vlen(t))
 345                                 return -EINVAL;
 346
 347                         bit_offset = btf_member_bit_offset(t, access_idx);
 348                         spec->bit_offset += bit_offset;
 349
 350                         m = btf_members(t) + access_idx;
 351                         if (m->name_off) {
 352                                 name = btf__name_by_offset(btf, m->name_off);
 353                                 if (str_is_empty(name))
 354                                         return -EINVAL;
 355
 356                                 acc->type_id = id;
 357                                 acc->idx = access_idx;
 358                                 acc->name = name;
 359                                 spec->len++;
 360                         }
 361
 362                         id = m->type;
 363                 } else if (btf_is_array(t)) {
 364                         const struct btf_array *a = btf_array(t);
 365                         bool flex;
 366
 367                         t = skip_mods_and_typedefs(btf, a->type, &id);
 368                         if (!t)
 369                                 return -EINVAL;
 370
 371                         flex = is_flex_arr(btf, acc - 1, a);
 372                         if (!flex && access_idx >= a->nelems)
 373                                 return -EINVAL;
 374
 375                         spec->spec[spec->len].type_id = id;
 376                         spec->spec[spec->len].idx = access_idx;
 377                         spec->len++;
 378
 379                         sz = btf__resolve_size(btf, id);
 380                         if (sz < 0)
 381                                 return sz;
 382                         spec->bit_offset += access_idx * sz * 8;
 383                 } else {
 384                         pr_warn("prog '%s': relo for [%u] %s (at idx %d) captures type [%d] of unexpected kind %s\n",
 385                                 prog_name, relo->type_id, spec_str, i, id, btf_kind_str(t));
 386                         return -EINVAL;
 387                 }
 388         }
 389
 390         return 0;
 391 }
 392
 393 /* Check two types for compatibility for the purpose of field access
 394  * relocation. const/volatile/restrict and typedefs are skipped to ensure we
 395  * are relocating semantically compatible entities:
 396  *   - any two STRUCTs/UNIONs are compatible and can be mixed;
 397  *   - any two FWDs are compatible, if their names match (modulo flavor suffix);
 398  *   - any two PTRs are always compatible;
 399  *   - for ENUMs, names should be the same (ignoring flavor suffix) or at
 400  *     least one of enums should be anonymous;
 401  *   - for ENUMs, check sizes, names are ignored;
 402  *   - for INT, size and signedness are ignored;
 403  *   - any two FLOATs are always compatible;
 404  *   - for ARRAY, dimensionality is ignored, element types are checked for
 405  *     compatibility recursively;
 406  *   - everything else shouldn't be ever a target of relocation.
 407  * These rules are not set in stone and probably will be adjusted as we get
 408  * more experience with using BPF CO-RE relocations.
 409  */
 410 static int bpf_core_fields_are_compat(const struct btf *local_btf,
 411                                       __u32 local_id,
 412                                       const struct btf *targ_btf,
 413                                       __u32 targ_id)
 414 {
 415         const struct btf_type *local_type, *targ_type;
 416
 417 recur:
 418         local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
 419         targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
 420         if (!local_type || !targ_type)
 421                 return -EINVAL;
 422
 423         if (btf_is_composite(local_type) && btf_is_composite(targ_type))
 424                 return 1;
 425         if (!btf_kind_core_compat(local_type, targ_type))
 426                 return 0;
 427
 428         switch (btf_kind(local_type)) {
 429         case BTF_KIND_PTR:
 430         case BTF_KIND_FLOAT:
 431                 return 1;
 432         case BTF_KIND_FWD:
 433         case BTF_KIND_ENUM64:
 434         case BTF_KIND_ENUM: {
 435                 const char *local_name, *targ_name;
 436                 size_t local_len, targ_len;
 437
 438                 local_name = btf__name_by_offset(local_btf,
 439                                                  local_type->name_off);
 440                 targ_name = btf__name_by_offset(targ_btf, targ_type->name_off);
 441                 local_len = bpf_core_essential_name_len(local_name);
 442                 targ_len = bpf_core_essential_name_len(targ_name);
 443                 /* one of them is anonymous or both w/ same flavor-less names */
 444                 return local_len == 0 || targ_len == 0 ||
 445                        (local_len == targ_len &&
 446                         strncmp(local_name, targ_name, local_len) == 0);
 447         }
 448         case BTF_KIND_INT:
 449                 /* just reject deprecated bitfield-like integers; all other
 450                  * integers are by default compatible between each other
 451                  */
 452                 return btf_int_offset(local_type) == 0 &&
 453                        btf_int_offset(targ_type) == 0;
 454         case BTF_KIND_ARRAY:
 455                 local_id = btf_array(local_type)->type;
 456                 targ_id = btf_array(targ_type)->type;
 457                 goto recur;
 458         default:
 459                 return 0;
 460         }
 461 }
 462
 463 /*
 464  * Given single high-level named field accessor in local type, find
 465  * corresponding high-level accessor for a target type. Along the way,
 466  * maintain low-level spec for target as well. Also keep updating target
 467  * bit offset.
 468  *
 469  * Searching is performed through recursive exhaustive enumeration of all
 470  * fields of a struct/union. If there are any anonymous (embedded)
 471  * structs/unions, they are recursively searched as well. If field with
 472  * desired name is found, check compatibility between local and target types,
 473  * before returning result.
 474  *
 475  * 1 is returned, if field is found.
 476  * 0 is returned if no compatible field is found.
 477  * <0 is returned on error.
 478  */
 479 static int bpf_core_match_member(const struct btf *local_btf,
 480                                  const struct bpf_core_accessor *local_acc,
 481                                  const struct btf *targ_btf,
 482                                  __u32 targ_id,
 483                                  struct bpf_core_spec *spec,
 484                                  __u32 *next_targ_id)
 485 {
 486         const struct btf_type *local_type, *targ_type;
 487         const struct btf_member *local_member, *m;
 488         const char *local_name, *targ_name;
 489         __u32 local_id;
 490         int i, n, found;
 491
 492         targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
 493         if (!targ_type)
 494                 return -EINVAL;
 495         if (!btf_is_composite(targ_type))
 496                 return 0;
 497
 498         local_id = local_acc->type_id;
 499         local_type = btf_type_by_id(local_btf, local_id);
 500         local_member = btf_members(local_type) + local_acc->idx;
 501         local_name = btf__name_by_offset(local_btf, local_member->name_off);
 502
 503         n = btf_vlen(targ_type);
 504         m = btf_members(targ_type);
 505         for (i = 0; i < n; i++, m++) {
 506                 __u32 bit_offset;
 507
 508                 bit_offset = btf_member_bit_offset(targ_type, i);
 509
 510                 /* too deep struct/union/array nesting */
 511                 if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
 512                         return -E2BIG;
 513
 514                 /* speculate this member will be the good one */
 515                 spec->bit_offset += bit_offset;
 516                 spec->raw_spec[spec->raw_len++] = i;
 517
 518                 targ_name = btf__name_by_offset(targ_btf, m->name_off);
 519                 if (str_is_empty(targ_name)) {
 520                         /* embedded struct/union, we need to go deeper */
 521                         found = bpf_core_match_member(local_btf, local_acc,
 522                                                       targ_btf, m->type,
 523                                                       spec, next_targ_id);
 524                         if (found) /* either found or error */
 525                                 return found;
 526                 } else if (strcmp(local_name, targ_name) == 0) {
 527                         /* matching named field */
 528                         struct bpf_core_accessor *targ_acc;
 529
 530                         targ_acc = &spec->spec[spec->len++];
 531                         targ_acc->type_id = targ_id;
 532                         targ_acc->idx = i;
 533                         targ_acc->name = targ_name;
 534
 535                         *next_targ_id = m->type;
 536                         found = bpf_core_fields_are_compat(local_btf,
 537                                                            local_member->type,
 538                                                            targ_btf, m->type);
 539                         if (!found)
 540                                 spec->len--; /* pop accessor */
 541                         return found;
 542                 }
 543                 /* member turned out not to be what we looked for */
 544                 spec->bit_offset -= bit_offset;
 545                 spec->raw_len--;
 546         }
 547
 548         return 0;
 549 }
 550
 551 /*
 552  * Try to match local spec to a target type and, if successful, produce full
 553  * target spec (high-level, low-level + bit offset).
 554  */
 555 static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
 556                                const struct btf *targ_btf, __u32 targ_id,
 557                                struct bpf_core_spec *targ_spec)
 558 {
 559         const struct btf_type *targ_type;
 560         const struct bpf_core_accessor *local_acc;
 561         struct bpf_core_accessor *targ_acc;
 562         int i, sz, matched;
 563         __u32 name_off;
 564
 565         memset(targ_spec, 0, sizeof(*targ_spec));
 566         targ_spec->btf = targ_btf;
 567         targ_spec->root_type_id = targ_id;
 568         targ_spec->relo_kind = local_spec->relo_kind;
 569
 570         if (core_relo_is_type_based(local_spec->relo_kind)) {
 571                 return bpf_core_types_are_compat(local_spec->btf,
 572                                                  local_spec->root_type_id,
 573                                                  targ_btf, targ_id);
 574         }
 575
 576         local_acc = &local_spec->spec[0];
 577         targ_acc = &targ_spec->spec[0];
 578
 579         if (core_relo_is_enumval_based(local_spec->relo_kind)) {
 580                 size_t local_essent_len, targ_essent_len;
 581                 const char *targ_name;
 582
 583                 /* has to resolve to an enum */
 584                 targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id, &targ_id);
 585                 if (!btf_is_any_enum(targ_type))
 586                         return 0;
 587
 588                 local_essent_len = bpf_core_essential_name_len(local_acc->name);
 589
 590                 for (i = 0; i < btf_vlen(targ_type); i++) {
 591                         if (btf_is_enum(targ_type))
 592                                 name_off = btf_enum(targ_type)[i].name_off;
 593                         else
 594                                 name_off = btf_enum64(targ_type)[i].name_off;
 595
 596                         targ_name = btf__name_by_offset(targ_spec->btf, name_off);
 597                         targ_essent_len = bpf_core_essential_name_len(targ_name);
 598                         if (targ_essent_len != local_essent_len)
 599                                 continue;
 600                         if (strncmp(local_acc->name, targ_name, local_essent_len) == 0) {
 601                                 targ_acc->type_id = targ_id;
 602                                 targ_acc->idx = i;
 603                                 targ_acc->name = targ_name;
 604                                 targ_spec->len++;
 605                                 targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
 606                                 targ_spec->raw_len++;
 607                                 return 1;
 608                         }
 609                 }
 610                 return 0;
 611         }
 612
 613         if (!core_relo_is_field_based(local_spec->relo_kind))
 614                 return -EINVAL;
 615
 616         for (i = 0; i < local_spec->len; i++, local_acc++, targ_acc++) {
 617                 targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id,
 618                                                    &targ_id);
 619                 if (!targ_type)
 620                         return -EINVAL;
 621
 622                 if (local_acc->name) {
 623                         matched = bpf_core_match_member(local_spec->btf,
 624                                                         local_acc,
 625                                                         targ_btf, targ_id,
 626                                                         targ_spec, &targ_id);
 627                         if (matched <= 0)
 628                                 return matched;
 629                 } else {
 630                         /* for i=0, targ_id is already treated as array element
 631                          * type (because it's the original struct), for others
 632                          * we should find array element type first
 633                          */
 634                         if (i > 0) {
 635                                 const struct btf_array *a;
 636                                 bool flex;
 637
 638                                 if (!btf_is_array(targ_type))
 639                                         return 0;
 640
 641                                 a = btf_array(targ_type);
 642                                 flex = is_flex_arr(targ_btf, targ_acc - 1, a);
 643                                 if (!flex && local_acc->idx >= a->nelems)
 644                                         return 0;
 645                                 if (!skip_mods_and_typedefs(targ_btf, a->type,
 646                                                             &targ_id))
 647                                         return -EINVAL;
 648                         }
 649
 650                         /* too deep struct/union/array nesting */
 651                         if (targ_spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
 652                                 return -E2BIG;
 653
 654                         targ_acc->type_id = targ_id;
 655                         targ_acc->idx = local_acc->idx;
 656                         targ_acc->name = NULL;
 657                         targ_spec->len++;
 658                         targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
 659                         targ_spec->raw_len++;
 660
 661                         sz = btf__resolve_size(targ_btf, targ_id);
 662                         if (sz < 0)
 663                                 return sz;
 664                         targ_spec->bit_offset += local_acc->idx * sz * 8;
 665                 }
 666         }
 667
 668         return 1;
 669 }
 670
 671 static int bpf_core_calc_field_relo(const char *prog_name,
 672                                     const struct bpf_core_relo *relo,
 673                                     const struct bpf_core_spec *spec,
 674                                     __u64 *val, __u32 *field_sz, __u32 *type_id,
 675                                     bool *validate)
 676 {
 677         const struct bpf_core_accessor *acc;
 678         const struct btf_type *t;
 679         __u32 byte_off, byte_sz, bit_off, bit_sz, field_type_id;
 680         const struct btf_member *m;
 681         const struct btf_type *mt;
 682         bool bitfield;
 683         __s64 sz;
 684
 685         *field_sz = 0;
 686
 687         if (relo->kind == BPF_CORE_FIELD_EXISTS) {
 688                 *val = spec ? 1 : 0;
 689                 return 0;
 690         }
 691
 692         if (!spec)
 693                 return -EUCLEAN; /* request instruction poisoning */
 694
 695         acc = &spec->spec[spec->len - 1];
 696         t = btf_type_by_id(spec->btf, acc->type_id);
 697
 698         /* a[n] accessor needs special handling */
 699         if (!acc->name) {
 700                 if (relo->kind == BPF_CORE_FIELD_BYTE_OFFSET) {
 701                         *val = spec->bit_offset / 8;
 702                         /* remember field size for load/store mem size */
 703                         sz = btf__resolve_size(spec->btf, acc->type_id);
 704                         if (sz < 0)
 705                                 return -EINVAL;
 706                         *field_sz = sz;
 707                         *type_id = acc->type_id;
 708                 } else if (relo->kind == BPF_CORE_FIELD_BYTE_SIZE) {
 709                         sz = btf__resolve_size(spec->btf, acc->type_id);
 710                         if (sz < 0)
 711                                 return -EINVAL;
 712                         *val = sz;
 713                 } else {
 714                         pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access\n",
 715                                 prog_name, relo->kind, relo->insn_off / 8);
 716                         return -EINVAL;
 717                 }
 718                 if (validate)
 719                         *validate = true;
 720                 return 0;
 721         }
 722
 723         m = btf_members(t) + acc->idx;
 724         mt = skip_mods_and_typedefs(spec->btf, m->type, &field_type_id);
 725         bit_off = spec->bit_offset;
 726         bit_sz = btf_member_bitfield_size(t, acc->idx);
 727
 728         bitfield = bit_sz > 0;
 729         if (bitfield) {
 730                 byte_sz = mt->size;
 731                 byte_off = bit_off / 8 / byte_sz * byte_sz;
 732                 /* figure out smallest int size necessary for bitfield load */
 733                 while (bit_off + bit_sz - byte_off * 8 > byte_sz * 8) {
 734                         if (byte_sz >= 8) {
 735                                 /* bitfield can't be read with 64-bit read */
 736                                 pr_warn("prog '%s': relo %d at insn #%d can't be satisfied for bitfield\n",
 737                                         prog_name, relo->kind, relo->insn_off / 8);
 738                                 return -E2BIG;
 739                         }
 740                         byte_sz *= 2;
 741                         byte_off = bit_off / 8 / byte_sz * byte_sz;
 742                 }
 743         } else {
 744                 sz = btf__resolve_size(spec->btf, field_type_id);
 745                 if (sz < 0)
 746                         return -EINVAL;
 747                 byte_sz = sz;
 748                 byte_off = spec->bit_offset / 8;
 749                 bit_sz = byte_sz * 8;
 750         }
 751
 752         /* for bitfields, all the relocatable aspects are ambiguous and we
 753          * might disagree with compiler, so turn off validation of expected
 754          * value, except for signedness
 755          */
 756         if (validate)
 757                 *validate = !bitfield;
 758
 759         switch (relo->kind) {
 760         case BPF_CORE_FIELD_BYTE_OFFSET:
 761                 *val = byte_off;
 762                 if (!bitfield) {
 763                         *field_sz = byte_sz;
 764                         *type_id = field_type_id;
 765                 }
 766                 break;
 767         case BPF_CORE_FIELD_BYTE_SIZE:
 768                 *val = byte_sz;
 769                 break;
 770         case BPF_CORE_FIELD_SIGNED:
 771                 *val = (btf_is_any_enum(mt) && BTF_INFO_KFLAG(mt->info)) ||
 772                        (btf_int_encoding(mt) & BTF_INT_SIGNED);
 773                 if (validate)
 774                         *validate = true; /* signedness is never ambiguous */
 775                 break;
 776         case BPF_CORE_FIELD_LSHIFT_U64:
 777 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 778                 *val = 64 - (bit_off + bit_sz - byte_off  * 8);
 779 #else
 780                 *val = (8 - byte_sz) * 8 + (bit_off - byte_off * 8);
 781 #endif
 782                 break;
 783         case BPF_CORE_FIELD_RSHIFT_U64:
 784                 *val = 64 - bit_sz;
 785                 if (validate)
 786                         *validate = true; /* right shift is never ambiguous */
 787                 break;
 788         case BPF_CORE_FIELD_EXISTS:
 789         default:
 790                 return -EOPNOTSUPP;
 791         }
 792
 793         return 0;
 794 }
 795
 796 static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo,
 797                                    const struct bpf_core_spec *spec,
 798                                    __u64 *val, bool *validate)
 799 {
 800         __s64 sz;
 801
 802         /* by default, always check expected value in bpf_insn */
 803         if (validate)
 804                 *validate = true;
 805
 806         /* type-based relos return zero when target type is not found */
 807         if (!spec) {
 808                 *val = 0;
 809                 return 0;
 810         }
 811
 812         switch (relo->kind) {
 813         case BPF_CORE_TYPE_ID_TARGET:
 814                 *val = spec->root_type_id;
 815                 /* type ID, embedded in bpf_insn, might change during linking,
 816                  * so enforcing it is pointless
 817                  */
 818                 if (validate)
 819                         *validate = false;
 820                 break;
 821         case BPF_CORE_TYPE_EXISTS:
 822                 *val = 1;
 823                 break;
 824         case BPF_CORE_TYPE_SIZE:
 825                 sz = btf__resolve_size(spec->btf, spec->root_type_id);
 826                 if (sz < 0)
 827                         return -EINVAL;
 828                 *val = sz;
 829                 break;
 830         case BPF_CORE_TYPE_ID_LOCAL:
 831         /* BPF_CORE_TYPE_ID_LOCAL is handled specially and shouldn't get here */
 832         default:
 833                 return -EOPNOTSUPP;
 834         }
 835
 836         return 0;
 837 }
 838
 839 static int bpf_core_calc_enumval_relo(const struct bpf_core_relo *relo,
 840                                       const struct bpf_core_spec *spec,
 841                                       __u64 *val)
 842 {
 843         const struct btf_type *t;
 844
 845         switch (relo->kind) {
 846         case BPF_CORE_ENUMVAL_EXISTS:
 847                 *val = spec ? 1 : 0;
 848                 break;
 849         case BPF_CORE_ENUMVAL_VALUE:
 850                 if (!spec)
 851                         return -EUCLEAN; /* request instruction poisoning */
 852                 t = btf_type_by_id(spec->btf, spec->spec[0].type_id);
 853                 if (btf_is_enum(t))
 854                         *val = btf_enum(t)[spec->spec[0].idx].val;
 855                 else
 856                         *val = btf_enum64_value(btf_enum64(t) + spec->spec[0].idx);
 857                 break;
 858         default:
 859                 return -EOPNOTSUPP;
 860         }
 861
 862         return 0;
 863 }
 864
 865 /* Calculate original and target relocation values, given local and target
 866  * specs and relocation kind. These values are calculated for each candidate.
 867  * If there are multiple candidates, resulting values should all be consistent
 868  * with each other. Otherwise, libbpf will refuse to proceed due to ambiguity.
 869  * If instruction has to be poisoned, *poison will be set to true.
 870  */
 871 static int bpf_core_calc_relo(const char *prog_name,
 872                               const struct bpf_core_relo *relo,
 873                               int relo_idx,
 874                               const struct bpf_core_spec *local_spec,
 875                               const struct bpf_core_spec *targ_spec,
 876                               struct bpf_core_relo_res *res)
 877 {
 878         int err = -EOPNOTSUPP;
 879
 880         res->orig_val = 0;
 881         res->new_val = 0;
 882         res->poison = false;
 883         res->validate = true;
 884         res->fail_memsz_adjust = false;
 885         res->orig_sz = res->new_sz = 0;
 886         res->orig_type_id = res->new_type_id = 0;
 887
 888         if (core_relo_is_field_based(relo->kind)) {
 889                 err = bpf_core_calc_field_relo(prog_name, relo, local_spec,
 890                                                &res->orig_val, &res->orig_sz,
 891                                                &res->orig_type_id, &res->validate);
 892                 err = err ?: bpf_core_calc_field_relo(prog_name, relo, targ_spec,
 893                                                       &res->new_val, &res->new_sz,
 894                                                       &res->new_type_id, NULL);
 895                 if (err)
 896                         goto done;
 897                 /* Validate if it's safe to adjust load/store memory size.
 898                  * Adjustments are performed only if original and new memory
 899                  * sizes differ.
 900                  */
 901                 res->fail_memsz_adjust = false;
 902                 if (res->orig_sz != res->new_sz) {
 903                         const struct btf_type *orig_t, *new_t;
 904
 905                         orig_t = btf_type_by_id(local_spec->btf, res->orig_type_id);
 906                         new_t = btf_type_by_id(targ_spec->btf, res->new_type_id);
 907
 908                         /* There are two use cases in which it's safe to
 909                          * adjust load/store's mem size:
 910                          *   - reading a 32-bit kernel pointer, while on BPF
 911                          *   size pointers are always 64-bit; in this case
 912                          *   it's safe to "downsize" instruction size due to
 913                          *   pointer being treated as unsigned integer with
 914                          *   zero-extended upper 32-bits;
 915                          *   - reading unsigned integers, again due to
 916                          *   zero-extension is preserving the value correctly.
 917                          *
 918                          * In all other cases it's incorrect to attempt to
 919                          * load/store field because read value will be
 920                          * incorrect, so we poison relocated instruction.
 921                          */
 922                         if (btf_is_ptr(orig_t) && btf_is_ptr(new_t))
 923                                 goto done;
 924                         if (btf_is_int(orig_t) && btf_is_int(new_t) &&
 925                             btf_int_encoding(orig_t) != BTF_INT_SIGNED &&
 926                             btf_int_encoding(new_t) != BTF_INT_SIGNED)
 927                                 goto done;
 928
 929                         /* mark as invalid mem size adjustment, but this will
 930                          * only be checked for LDX/STX/ST insns
 931                          */
 932                         res->fail_memsz_adjust = true;
 933                 }
 934         } else if (core_relo_is_type_based(relo->kind)) {
 935                 err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val, &res->validate);
 936                 err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val, NULL);
 937         } else if (core_relo_is_enumval_based(relo->kind)) {
 938                 err = bpf_core_calc_enumval_relo(relo, local_spec, &res->orig_val);
 939                 err = err ?: bpf_core_calc_enumval_relo(relo, targ_spec, &res->new_val);
 940         }
 941
 942 done:
 943         if (err == -EUCLEAN) {
 944                 /* EUCLEAN is used to signal instruction poisoning request */
 945                 res->poison = true;
 946                 err = 0;
 947         } else if (err == -EOPNOTSUPP) {
 948                 /* EOPNOTSUPP means unknown/unsupported relocation */
 949                 pr_warn("prog '%s': relo #%d: unrecognized CO-RE relocation %s (%d) at insn #%d\n",
 950                         prog_name, relo_idx, core_relo_kind_str(relo->kind),
 951                         relo->kind, relo->insn_off / 8);
 952         }
 953
 954         return err;
 955 }
 956
 957 /*
 958  * Turn instruction for which CO_RE relocation failed into invalid one with
 959  * distinct signature.
 960  */
 961 static void bpf_core_poison_insn(const char *prog_name, int relo_idx,
 962                                  int insn_idx, struct bpf_insn *insn)
 963 {
 964         pr_debug("prog '%s': relo #%d: substituting insn #%d w/ invalid insn\n",
 965                  prog_name, relo_idx, insn_idx);
 966         insn->code = BPF_JMP | BPF_CALL;
 967         insn->dst_reg = 0;
 968         insn->src_reg = 0;
 969         insn->off = 0;
 970         /* if this instruction is reachable (not a dead code),
 971          * verifier will complain with the following message:
 972          * invalid func unknown#195896080
 973          */
 974         insn->imm = 195896080; /* => 0xbad2310 => "bad relo" */
 975 }
 976
 977 static int insn_bpf_size_to_bytes(struct bpf_insn *insn)
 978 {
 979         switch (BPF_SIZE(insn->code)) {
 980         case BPF_DW: return 8;
 981         case BPF_W: return 4;
 982         case BPF_H: return 2;
 983         case BPF_B: return 1;
 984         default: return -1;
 985         }
 986 }
 987
 988 static int insn_bytes_to_bpf_size(__u32 sz)
 989 {
 990         switch (sz) {
 991         case 8: return BPF_DW;
 992         case 4: return BPF_W;
 993         case 2: return BPF_H;
 994         case 1: return BPF_B;
 995         default: return -1;
 996         }
 997 }
 998
 999 /*
1000  * Patch relocatable BPF instruction.
1001  *
1002  * Patched value is determined by relocation kind and target specification.
1003  * For existence relocations target spec will be NULL if field/type is not found.
1004  * Expected insn->imm value is determined using relocation kind and local
1005  * spec, and is checked before patching instruction. If actual insn->imm value
1006  * is wrong, bail out with error.
1007  *
1008  * Currently supported classes of BPF instruction are:
1009  * 1. rX = <imm> (assignment with immediate operand);
1010  * 2. rX += <imm> (arithmetic operations with immediate operand);
1011  * 3. rX = <imm64> (load with 64-bit immediate value);
1012  * 4. rX = *(T *)(rY + <off>), where T is one of {u8, u16, u32, u64};
1013  * 5. *(T *)(rX + <off>) = rY, where T is one of {u8, u16, u32, u64};
1014  * 6. *(T *)(rX + <off>) = <imm>, where T is one of {u8, u16, u32, u64}.
1015  */
1016 int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
1017                         int insn_idx, const struct bpf_core_relo *relo,
1018                         int relo_idx, const struct bpf_core_relo_res *res)
1019 {
1020         __u64 orig_val, new_val;
1021         __u8 class;
1022
1023         class = BPF_CLASS(insn->code);
1024
1025         if (res->poison) {
1026 poison:
1027                 /* poison second part of ldimm64 to avoid confusing error from
1028                  * verifier about "unknown opcode 00"
1029                  */
1030                 if (is_ldimm64_insn(insn))
1031                         bpf_core_poison_insn(prog_name, relo_idx, insn_idx + 1, insn + 1);
1032                 bpf_core_poison_insn(prog_name, relo_idx, insn_idx, insn);
1033                 return 0;
1034         }
1035
1036         orig_val = res->orig_val;
1037         new_val = res->new_val;
1038
1039         switch (class) {
1040         case BPF_ALU:
1041         case BPF_ALU64:
1042                 if (BPF_SRC(insn->code) != BPF_K)
1043                         return -EINVAL;
1044                 if (res->validate && insn->imm != orig_val) {
1045                         pr_warn("prog '%s': relo #%d: unexpected insn #%d (ALU/ALU64) value: got %u, exp %llu -> %llu\n",
1046                                 prog_name, relo_idx,
1047                                 insn_idx, insn->imm, (unsigned long long)orig_val,
1048                                 (unsigned long long)new_val);
1049                         return -EINVAL;
1050                 }
1051                 orig_val = insn->imm;
1052                 insn->imm = new_val;
1053                 pr_debug("prog '%s': relo #%d: patched insn #%d (ALU/ALU64) imm %llu -> %llu\n",
1054                          prog_name, relo_idx, insn_idx,
1055                          (unsigned long long)orig_val, (unsigned long long)new_val);
1056                 break;
1057         case BPF_LDX:
1058         case BPF_ST:
1059         case BPF_STX:
1060                 if (res->validate && insn->off != orig_val) {
1061                         pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDX/ST/STX) value: got %u, exp %llu -> %llu\n",
1062                                 prog_name, relo_idx, insn_idx, insn->off, (unsigned long long)orig_val,
1063                                 (unsigned long long)new_val);
1064                         return -EINVAL;
1065                 }
1066                 if (new_val > SHRT_MAX) {
1067                         pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) value too big: %llu\n",
1068                                 prog_name, relo_idx, insn_idx, (unsigned long long)new_val);
1069                         return -ERANGE;
1070                 }
1071                 if (res->fail_memsz_adjust) {
1072                         pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) accesses field incorrectly. "
1073                                 "Make sure you are accessing pointers, unsigned integers, or fields of matching type and size.\n",
1074                                 prog_name, relo_idx, insn_idx);
1075                         goto poison;
1076                 }
1077
1078                 orig_val = insn->off;
1079                 insn->off = new_val;
1080                 pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) off %llu -> %llu\n",
1081                          prog_name, relo_idx, insn_idx, (unsigned long long)orig_val,
1082                          (unsigned long long)new_val);
1083
1084                 if (res->new_sz != res->orig_sz) {
1085                         int insn_bytes_sz, insn_bpf_sz;
1086
1087                         insn_bytes_sz = insn_bpf_size_to_bytes(insn);
1088                         if (insn_bytes_sz != res->orig_sz) {
1089                                 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) unexpected mem size: got %d, exp %u\n",
1090                                         prog_name, relo_idx, insn_idx, insn_bytes_sz, res->orig_sz);
1091                                 return -EINVAL;
1092                         }
1093
1094                         insn_bpf_sz = insn_bytes_to_bpf_size(res->new_sz);
1095                         if (insn_bpf_sz < 0) {
1096                                 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) invalid new mem size: %u\n",
1097                                         prog_name, relo_idx, insn_idx, res->new_sz);
1098                                 return -EINVAL;
1099                         }
1100
1101                         insn->code = BPF_MODE(insn->code) | insn_bpf_sz | BPF_CLASS(insn->code);
1102                         pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) mem_sz %u -> %u\n",
1103                                  prog_name, relo_idx, insn_idx, res->orig_sz, res->new_sz);
1104                 }
1105                 break;
1106         case BPF_LD: {
1107                 __u64 imm;
1108
1109                 if (!is_ldimm64_insn(insn) ||
1110                     insn[0].src_reg != 0 || insn[0].off != 0 ||
1111                     insn[1].code != 0 || insn[1].dst_reg != 0 ||
1112                     insn[1].src_reg != 0 || insn[1].off != 0) {
1113                         pr_warn("prog '%s': relo #%d: insn #%d (LDIMM64) has unexpected form\n",
1114                                 prog_name, relo_idx, insn_idx);
1115                         return -EINVAL;
1116                 }
1117
1118                 imm = (__u32)insn[0].imm | ((__u64)insn[1].imm << 32);
1119                 if (res->validate && imm != orig_val) {
1120                         pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %llu -> %llu\n",
1121                                 prog_name, relo_idx,
1122                                 insn_idx, (unsigned long long)imm,
1123                                 (unsigned long long)orig_val, (unsigned long long)new_val);
1124                         return -EINVAL;
1125                 }
1126
1127                 insn[0].imm = new_val;
1128                 insn[1].imm = new_val >> 32;
1129                 pr_debug("prog '%s': relo #%d: patched insn #%d (LDIMM64) imm64 %llu -> %llu\n",
1130                          prog_name, relo_idx, insn_idx,
1131                          (unsigned long long)imm, (unsigned long long)new_val);
1132                 break;
1133         }
1134         default:
1135                 pr_warn("prog '%s': relo #%d: trying to relocate unrecognized insn #%d, code:0x%x, src:0x%x, dst:0x%x, off:0x%x, imm:0x%x\n",
1136                         prog_name, relo_idx, insn_idx, insn->code,
1137                         insn->src_reg, insn->dst_reg, insn->off, insn->imm);
1138                 return -EINVAL;
1139         }
1140
1141         return 0;
1142 }
1143
1144 /* Output spec definition in the format:
1145  * [<type-id>] (<type-name>) + <raw-spec> => <offset>@<spec>,
1146  * where <spec> is a C-syntax view of recorded field access, e.g.: x.a[3].b
1147  */
1148 int bpf_core_format_spec(char *buf, size_t buf_sz, const struct bpf_core_spec *spec)
1149 {
1150         const struct btf_type *t;
1151         const char *s;
1152         __u32 type_id;
1153         int i, len = 0;
1154
1155 #define append_buf(fmt, args...)                                \
1156         ({                                                      \
1157                 int r;                                          \
1158                 r = snprintf(buf, buf_sz, fmt, ##args);         \
1159                 len += r;                                       \
1160                 if (r >= buf_sz)                                \
1161                         r = buf_sz;                             \
1162                 buf += r;                                       \
1163                 buf_sz -= r;                                    \
1164         })
1165
1166         type_id = spec->root_type_id;
1167         t = btf_type_by_id(spec->btf, type_id);
1168         s = btf__name_by_offset(spec->btf, t->name_off);
1169
1170         append_buf("<%s> [%u] %s %s",
1171                    core_relo_kind_str(spec->relo_kind),
1172                    type_id, btf_kind_str(t), str_is_empty(s) ? "<anon>" : s);
1173
1174         if (core_relo_is_type_based(spec->relo_kind))
1175                 return len;
1176
1177         if (core_relo_is_enumval_based(spec->relo_kind)) {
1178                 t = skip_mods_and_typedefs(spec->btf, type_id, NULL);
1179                 if (btf_is_enum(t)) {
1180                         const struct btf_enum *e;
1181                         const char *fmt_str;
1182
1183                         e = btf_enum(t) + spec->raw_spec[0];
1184                         s = btf__name_by_offset(spec->btf, e->name_off);
1185                         fmt_str = BTF_INFO_KFLAG(t->info) ? "::%s = %d" : "::%s = %u";
1186                         append_buf(fmt_str, s, e->val);
1187                 } else {
1188                         const struct btf_enum64 *e;
1189                         const char *fmt_str;
1190
1191                         e = btf_enum64(t) + spec->raw_spec[0];
1192                         s = btf__name_by_offset(spec->btf, e->name_off);
1193                         fmt_str = BTF_INFO_KFLAG(t->info) ? "::%s = %lld" : "::%s = %llu";
1194                         append_buf(fmt_str, s, (unsigned long long)btf_enum64_value(e));
1195                 }
1196                 return len;
1197         }
1198
1199         if (core_relo_is_field_based(spec->relo_kind)) {
1200                 for (i = 0; i < spec->len; i++) {
1201                         if (spec->spec[i].name)
1202                                 append_buf(".%s", spec->spec[i].name);
1203                         else if (i > 0 || spec->spec[i].idx > 0)
1204                                 append_buf("[%u]", spec->spec[i].idx);
1205                 }
1206
1207                 append_buf(" (");
1208                 for (i = 0; i < spec->raw_len; i++)
1209                         append_buf("%s%d", i == 0 ? "" : ":", spec->raw_spec[i]);
1210
1211                 if (spec->bit_offset % 8)
1212                         append_buf(" @ offset %u.%u)", spec->bit_offset / 8, spec->bit_offset % 8);
1213                 else
1214                         append_buf(" @ offset %u)", spec->bit_offset / 8);
1215                 return len;
1216         }
1217
1218         return len;
1219 #undef append_buf
1220 }
1221
1222 /*
1223  * Calculate CO-RE relocation target result.
1224  *
1225  * The outline and important points of the algorithm:
1226  * 1. For given local type, find corresponding candidate target types.
1227  *    Candidate type is a type with the same "essential" name, ignoring
1228  *    everything after last triple underscore (___). E.g., `sample`,
1229  *    `sample___flavor_one`, `sample___flavor_another_one`, are all candidates
1230  *    for each other. Names with triple underscore are referred to as
1231  *    "flavors" and are useful, among other things, to allow to
1232  *    specify/support incompatible variations of the same kernel struct, which
1233  *    might differ between different kernel versions and/or build
1234  *    configurations.
1235  *
1236  *    N.B. Struct "flavors" could be generated by bpftool's BTF-to-C
1237  *    converter, when deduplicated BTF of a kernel still contains more than
1238  *    one different types with the same name. In that case, ___2, ___3, etc
1239  *    are appended starting from second name conflict. But start flavors are
1240  *    also useful to be defined "locally", in BPF program, to extract same
1241  *    data from incompatible changes between different kernel
1242  *    versions/configurations. For instance, to handle field renames between
1243  *    kernel versions, one can use two flavors of the struct name with the
1244  *    same common name and use conditional relocations to extract that field,
1245  *    depending on target kernel version.
1246  * 2. For each candidate type, try to match local specification to this
1247  *    candidate target type. Matching involves finding corresponding
1248  *    high-level spec accessors, meaning that all named fields should match,
1249  *    as well as all array accesses should be within the actual bounds. Also,
1250  *    types should be compatible (see bpf_core_fields_are_compat for details).
1251  * 3. It is supported and expected that there might be multiple flavors
1252  *    matching the spec. As long as all the specs resolve to the same set of
1253  *    offsets across all candidates, there is no error. If there is any
1254  *    ambiguity, CO-RE relocation will fail. This is necessary to accommodate
1255  *    imperfection of BTF deduplication, which can cause slight duplication of
1256  *    the same BTF type, if some directly or indirectly referenced (by
1257  *    pointer) type gets resolved to different actual types in different
1258  *    object files. If such a situation occurs, deduplicated BTF will end up
1259  *    with two (or more) structurally identical types, which differ only in
1260  *    types they refer to through pointer. This should be OK in most cases and
1261  *    is not an error.
1262  * 4. Candidate types search is performed by linearly scanning through all
1263  *    types in target BTF. It is anticipated that this is overall more
1264  *    efficient memory-wise and not significantly worse (if not better)
1265  *    CPU-wise compared to prebuilding a map from all local type names to
1266  *    a list of candidate type names. It's also sped up by caching resolved
1267  *    list of matching candidates per each local "root" type ID, that has at
1268  *    least one bpf_core_relo associated with it. This list is shared
1269  *    between multiple relocations for the same type ID and is updated as some
1270  *    of the candidates are pruned due to structural incompatibility.
1271  */
1272 int bpf_core_calc_relo_insn(const char *prog_name,
1273                             const struct bpf_core_relo *relo,
1274                             int relo_idx,
1275                             const struct btf *local_btf,
1276                             struct bpf_core_cand_list *cands,
1277                             struct bpf_core_spec *specs_scratch,
1278                             struct bpf_core_relo_res *targ_res)
1279 {
1280         struct bpf_core_spec *local_spec = &specs_scratch[0];
1281         struct bpf_core_spec *cand_spec = &specs_scratch[1];
1282         struct bpf_core_spec *targ_spec = &specs_scratch[2];
1283         struct bpf_core_relo_res cand_res;
1284         const struct btf_type *local_type;
1285         const char *local_name;
1286         __u32 local_id;
1287         char spec_buf[256];
1288         int i, j, err;
1289
1290         local_id = relo->type_id;
1291         local_type = btf_type_by_id(local_btf, local_id);
1292         local_name = btf__name_by_offset(local_btf, local_type->name_off);
1293         if (!local_name)
1294                 return -EINVAL;
1295
1296         err = bpf_core_parse_spec(prog_name, local_btf, relo, local_spec);
1297         if (err) {
1298                 const char *spec_str;
1299
1300                 spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
1301                 pr_warn("prog '%s': relo #%d: parsing [%d] %s %s + %s failed: %d\n",
1302                         prog_name, relo_idx, local_id, btf_kind_str(local_type),
1303                         str_is_empty(local_name) ? "<anon>" : local_name,
1304                         spec_str ?: "<?>", err);
1305                 return -EINVAL;
1306         }
1307
1308         bpf_core_format_spec(spec_buf, sizeof(spec_buf), local_spec);
1309         pr_debug("prog '%s': relo #%d: %s\n", prog_name, relo_idx, spec_buf);
1310
1311         /* TYPE_ID_LOCAL relo is special and doesn't need candidate search */
1312         if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) {
1313                 /* bpf_insn's imm value could get out of sync during linking */
1314                 memset(targ_res, 0, sizeof(*targ_res));
1315                 targ_res->validate = false;
1316                 targ_res->poison = false;
1317                 targ_res->orig_val = local_spec->root_type_id;
1318                 targ_res->new_val = local_spec->root_type_id;
1319                 return 0;
1320         }
1321
1322         /* libbpf doesn't support candidate search for anonymous types */
1323         if (str_is_empty(local_name)) {
1324                 pr_warn("prog '%s': relo #%d: <%s> (%d) relocation doesn't support anonymous types\n",
1325                         prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind);
1326                 return -EOPNOTSUPP;
1327         }
1328
1329         for (i = 0, j = 0; i < cands->len; i++) {
1330                 err = bpf_core_spec_match(local_spec, cands->cands[i].btf,
1331                                           cands->cands[i].id, cand_spec);
1332                 if (err < 0) {
1333                         bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
1334                         pr_warn("prog '%s': relo #%d: error matching candidate #%d %s: %d\n ",
1335                                 prog_name, relo_idx, i, spec_buf, err);
1336                         return err;
1337                 }
1338
1339                 bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
1340                 pr_debug("prog '%s': relo #%d: %s candidate #%d %s\n", prog_name,
1341                          relo_idx, err == 0 ? "non-matching" : "matching", i, spec_buf);
1342
1343                 if (err == 0)
1344                         continue;
1345
1346                 err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, cand_spec, &cand_res);
1347                 if (err)
1348                         return err;
1349
1350                 if (j == 0) {
1351                         *targ_res = cand_res;
1352                         *targ_spec = *cand_spec;
1353                 } else if (cand_spec->bit_offset != targ_spec->bit_offset) {
1354                         /* if there are many field relo candidates, they
1355                          * should all resolve to the same bit offset
1356                          */
1357                         pr_warn("prog '%s': relo #%d: field offset ambiguity: %u != %u\n",
1358                                 prog_name, relo_idx, cand_spec->bit_offset,
1359                                 targ_spec->bit_offset);
1360                         return -EINVAL;
1361                 } else if (cand_res.poison != targ_res->poison ||
1362                            cand_res.new_val != targ_res->new_val) {
1363                         /* all candidates should result in the same relocation
1364                          * decision and value, otherwise it's dangerous to
1365                          * proceed due to ambiguity
1366                          */
1367                         pr_warn("prog '%s': relo #%d: relocation decision ambiguity: %s %llu != %s %llu\n",
1368                                 prog_name, relo_idx,
1369                                 cand_res.poison ? "failure" : "success",
1370                                 (unsigned long long)cand_res.new_val,
1371                                 targ_res->poison ? "failure" : "success",
1372                                 (unsigned long long)targ_res->new_val);
1373                         return -EINVAL;
1374                 }
1375
1376                 cands->cands[j++] = cands->cands[i];
1377         }
1378
1379         /*
1380          * For BPF_CORE_FIELD_EXISTS relo or when used BPF program has field
1381          * existence checks or kernel version/config checks, it's expected
1382          * that we might not find any candidates. In this case, if field
1383          * wasn't found in any candidate, the list of candidates shouldn't
1384          * change at all, we'll just handle relocating appropriately,
1385          * depending on relo's kind.
1386          */
1387         if (j > 0)
1388                 cands->len = j;
1389
1390         /*
1391          * If no candidates were found, it might be both a programmer error,
1392          * as well as expected case, depending whether instruction w/
1393          * relocation is guarded in some way that makes it unreachable (dead
1394          * code) if relocation can't be resolved. This is handled in
1395          * bpf_core_patch_insn() uniformly by replacing that instruction with
1396          * BPF helper call insn (using invalid helper ID). If that instruction
1397          * is indeed unreachable, then it will be ignored and eliminated by
1398          * verifier. If it was an error, then verifier will complain and point
1399          * to a specific instruction number in its log.
1400          */
1401         if (j == 0) {
1402                 pr_debug("prog '%s': relo #%d: no matching targets found\n",
1403                          prog_name, relo_idx);
1404
1405                 /* calculate single target relo result explicitly */
1406                 err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, NULL, targ_res);
1407                 if (err)
1408                         return err;
1409         }
1410
1411         return 0;
1412 }