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
btf_kind_str(const struct btf_type * t)11 static const char *btf_kind_str(const struct btf_type *t)
12 {
13 return btf_type_str(t);
14 }
15
is_ldimm64_insn(struct bpf_insn * insn)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 *
skip_mods_and_typedefs(const struct btf * btf,u32 id,u32 * res_id)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
btf__name_by_offset(const struct btf * btf,u32 offset)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
btf__resolve_size(const struct btf * btf,u32 type_id)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
is_flex_arr(const struct btf * btf,const struct bpf_core_accessor * acc,const struct btf_array * arr)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
core_relo_kind_str(enum bpf_core_relo_kind kind)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_MATCHES: return "type_matches";
99 case BPF_CORE_TYPE_SIZE: return "type_size";
100 case BPF_CORE_ENUMVAL_EXISTS: return "enumval_exists";
101 case BPF_CORE_ENUMVAL_VALUE: return "enumval_value";
102 default: return "unknown";
103 }
104 }
105
core_relo_is_field_based(enum bpf_core_relo_kind kind)106 static bool core_relo_is_field_based(enum bpf_core_relo_kind kind)
107 {
108 switch (kind) {
109 case BPF_CORE_FIELD_BYTE_OFFSET:
110 case BPF_CORE_FIELD_BYTE_SIZE:
111 case BPF_CORE_FIELD_EXISTS:
112 case BPF_CORE_FIELD_SIGNED:
113 case BPF_CORE_FIELD_LSHIFT_U64:
114 case BPF_CORE_FIELD_RSHIFT_U64:
115 return true;
116 default:
117 return false;
118 }
119 }
120
core_relo_is_type_based(enum bpf_core_relo_kind kind)121 static bool core_relo_is_type_based(enum bpf_core_relo_kind kind)
122 {
123 switch (kind) {
124 case BPF_CORE_TYPE_ID_LOCAL:
125 case BPF_CORE_TYPE_ID_TARGET:
126 case BPF_CORE_TYPE_EXISTS:
127 case BPF_CORE_TYPE_MATCHES:
128 case BPF_CORE_TYPE_SIZE:
129 return true;
130 default:
131 return false;
132 }
133 }
134
core_relo_is_enumval_based(enum bpf_core_relo_kind kind)135 static bool core_relo_is_enumval_based(enum bpf_core_relo_kind kind)
136 {
137 switch (kind) {
138 case BPF_CORE_ENUMVAL_EXISTS:
139 case BPF_CORE_ENUMVAL_VALUE:
140 return true;
141 default:
142 return false;
143 }
144 }
145
__bpf_core_types_are_compat(const struct btf * local_btf,__u32 local_id,const struct btf * targ_btf,__u32 targ_id,int level)146 int __bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
147 const struct btf *targ_btf, __u32 targ_id, int level)
148 {
149 const struct btf_type *local_type, *targ_type;
150 int depth = 32; /* max recursion depth */
151
152 /* caller made sure that names match (ignoring flavor suffix) */
153 local_type = btf_type_by_id(local_btf, local_id);
154 targ_type = btf_type_by_id(targ_btf, targ_id);
155 if (!btf_kind_core_compat(local_type, targ_type))
156 return 0;
157
158 recur:
159 depth--;
160 if (depth < 0)
161 return -EINVAL;
162
163 local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
164 targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
165 if (!local_type || !targ_type)
166 return -EINVAL;
167
168 if (!btf_kind_core_compat(local_type, targ_type))
169 return 0;
170
171 switch (btf_kind(local_type)) {
172 case BTF_KIND_UNKN:
173 case BTF_KIND_STRUCT:
174 case BTF_KIND_UNION:
175 case BTF_KIND_ENUM:
176 case BTF_KIND_FWD:
177 case BTF_KIND_ENUM64:
178 return 1;
179 case BTF_KIND_INT:
180 /* just reject deprecated bitfield-like integers; all other
181 * integers are by default compatible between each other
182 */
183 return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0;
184 case BTF_KIND_PTR:
185 local_id = local_type->type;
186 targ_id = targ_type->type;
187 goto recur;
188 case BTF_KIND_ARRAY:
189 local_id = btf_array(local_type)->type;
190 targ_id = btf_array(targ_type)->type;
191 goto recur;
192 case BTF_KIND_FUNC_PROTO: {
193 struct btf_param *local_p = btf_params(local_type);
194 struct btf_param *targ_p = btf_params(targ_type);
195 __u16 local_vlen = btf_vlen(local_type);
196 __u16 targ_vlen = btf_vlen(targ_type);
197 int i, err;
198
199 if (local_vlen != targ_vlen)
200 return 0;
201
202 for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
203 if (level <= 0)
204 return -EINVAL;
205
206 skip_mods_and_typedefs(local_btf, local_p->type, &local_id);
207 skip_mods_and_typedefs(targ_btf, targ_p->type, &targ_id);
208 err = __bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id,
209 level - 1);
210 if (err <= 0)
211 return err;
212 }
213
214 /* tail recurse for return type check */
215 skip_mods_and_typedefs(local_btf, local_type->type, &local_id);
216 skip_mods_and_typedefs(targ_btf, targ_type->type, &targ_id);
217 goto recur;
218 }
219 default:
220 pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
221 btf_kind_str(local_type), local_id, targ_id);
222 return 0;
223 }
224 }
225
226 /*
227 * Turn bpf_core_relo into a low- and high-level spec representation,
228 * validating correctness along the way, as well as calculating resulting
229 * field bit offset, specified by accessor string. Low-level spec captures
230 * every single level of nestedness, including traversing anonymous
231 * struct/union members. High-level one only captures semantically meaningful
232 * "turning points": named fields and array indicies.
233 * E.g., for this case:
234 *
235 * struct sample {
236 * int __unimportant;
237 * struct {
238 * int __1;
239 * int __2;
240 * int a[7];
241 * };
242 * };
243 *
244 * struct sample *s = ...;
245 *
246 * int x = &s->a[3]; // access string = '0:1:2:3'
247 *
248 * Low-level spec has 1:1 mapping with each element of access string (it's
249 * just a parsed access string representation): [0, 1, 2, 3].
250 *
251 * High-level spec will capture only 3 points:
252 * - initial zero-index access by pointer (&s->... is the same as &s[0]...);
253 * - field 'a' access (corresponds to '2' in low-level spec);
254 * - array element #3 access (corresponds to '3' in low-level spec).
255 *
256 * Type-based relocations (TYPE_EXISTS/TYPE_MATCHES/TYPE_SIZE,
257 * TYPE_ID_LOCAL/TYPE_ID_TARGET) don't capture any field information. Their
258 * spec and raw_spec are kept empty.
259 *
260 * Enum value-based relocations (ENUMVAL_EXISTS/ENUMVAL_VALUE) use access
261 * string to specify enumerator's value index that need to be relocated.
262 */
bpf_core_parse_spec(const char * prog_name,const struct btf * btf,const struct bpf_core_relo * relo,struct bpf_core_spec * spec)263 int bpf_core_parse_spec(const char *prog_name, const struct btf *btf,
264 const struct bpf_core_relo *relo,
265 struct bpf_core_spec *spec)
266 {
267 int access_idx, parsed_len, i;
268 struct bpf_core_accessor *acc;
269 const struct btf_type *t;
270 const char *name, *spec_str;
271 __u32 id, name_off;
272 __s64 sz;
273
274 spec_str = btf__name_by_offset(btf, relo->access_str_off);
275 if (str_is_empty(spec_str) || *spec_str == ':')
276 return -EINVAL;
277
278 memset(spec, 0, sizeof(*spec));
279 spec->btf = btf;
280 spec->root_type_id = relo->type_id;
281 spec->relo_kind = relo->kind;
282
283 /* type-based relocations don't have a field access string */
284 if (core_relo_is_type_based(relo->kind)) {
285 if (strcmp(spec_str, "0"))
286 return -EINVAL;
287 return 0;
288 }
289
290 /* parse spec_str="0:1:2:3:4" into array raw_spec=[0, 1, 2, 3, 4] */
291 while (*spec_str) {
292 if (*spec_str == ':')
293 ++spec_str;
294 if (sscanf(spec_str, "%d%n", &access_idx, &parsed_len) != 1)
295 return -EINVAL;
296 if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
297 return -E2BIG;
298 spec_str += parsed_len;
299 spec->raw_spec[spec->raw_len++] = access_idx;
300 }
301
302 if (spec->raw_len == 0)
303 return -EINVAL;
304
305 t = skip_mods_and_typedefs(btf, relo->type_id, &id);
306 if (!t)
307 return -EINVAL;
308
309 access_idx = spec->raw_spec[0];
310 acc = &spec->spec[0];
311 acc->type_id = id;
312 acc->idx = access_idx;
313 spec->len++;
314
315 if (core_relo_is_enumval_based(relo->kind)) {
316 if (!btf_is_any_enum(t) || spec->raw_len > 1 || access_idx >= btf_vlen(t))
317 return -EINVAL;
318
319 /* record enumerator name in a first accessor */
320 name_off = btf_is_enum(t) ? btf_enum(t)[access_idx].name_off
321 : btf_enum64(t)[access_idx].name_off;
322 acc->name = btf__name_by_offset(btf, name_off);
323 return 0;
324 }
325
326 if (!core_relo_is_field_based(relo->kind))
327 return -EINVAL;
328
329 sz = btf__resolve_size(btf, id);
330 if (sz < 0)
331 return sz;
332 spec->bit_offset = access_idx * sz * 8;
333
334 for (i = 1; i < spec->raw_len; i++) {
335 t = skip_mods_and_typedefs(btf, id, &id);
336 if (!t)
337 return -EINVAL;
338
339 access_idx = spec->raw_spec[i];
340 acc = &spec->spec[spec->len];
341
342 if (btf_is_composite(t)) {
343 const struct btf_member *m;
344 __u32 bit_offset;
345
346 if (access_idx >= btf_vlen(t))
347 return -EINVAL;
348
349 bit_offset = btf_member_bit_offset(t, access_idx);
350 spec->bit_offset += bit_offset;
351
352 m = btf_members(t) + access_idx;
353 if (m->name_off) {
354 name = btf__name_by_offset(btf, m->name_off);
355 if (str_is_empty(name))
356 return -EINVAL;
357
358 acc->type_id = id;
359 acc->idx = access_idx;
360 acc->name = name;
361 spec->len++;
362 }
363
364 id = m->type;
365 } else if (btf_is_array(t)) {
366 const struct btf_array *a = btf_array(t);
367 bool flex;
368
369 t = skip_mods_and_typedefs(btf, a->type, &id);
370 if (!t)
371 return -EINVAL;
372
373 flex = is_flex_arr(btf, acc - 1, a);
374 if (!flex && access_idx >= a->nelems)
375 return -EINVAL;
376
377 spec->spec[spec->len].type_id = id;
378 spec->spec[spec->len].idx = access_idx;
379 spec->len++;
380
381 sz = btf__resolve_size(btf, id);
382 if (sz < 0)
383 return sz;
384 spec->bit_offset += access_idx * sz * 8;
385 } else {
386 pr_warn("prog '%s': relo for [%u] %s (at idx %d) captures type [%d] of unexpected kind %s\n",
387 prog_name, relo->type_id, spec_str, i, id, btf_kind_str(t));
388 return -EINVAL;
389 }
390 }
391
392 return 0;
393 }
394
395 /* Check two types for compatibility for the purpose of field access
396 * relocation. const/volatile/restrict and typedefs are skipped to ensure we
397 * are relocating semantically compatible entities:
398 * - any two STRUCTs/UNIONs are compatible and can be mixed;
399 * - any two FWDs are compatible, if their names match (modulo flavor suffix);
400 * - any two PTRs are always compatible;
401 * - for ENUMs, names should be the same (ignoring flavor suffix) or at
402 * least one of enums should be anonymous;
403 * - for ENUMs, check sizes, names are ignored;
404 * - for INT, size and signedness are ignored;
405 * - any two FLOATs are always compatible;
406 * - for ARRAY, dimensionality is ignored, element types are checked for
407 * compatibility recursively;
408 * - everything else shouldn't be ever a target of relocation.
409 * These rules are not set in stone and probably will be adjusted as we get
410 * more experience with using BPF CO-RE relocations.
411 */
bpf_core_fields_are_compat(const struct btf * local_btf,__u32 local_id,const struct btf * targ_btf,__u32 targ_id)412 static int bpf_core_fields_are_compat(const struct btf *local_btf,
413 __u32 local_id,
414 const struct btf *targ_btf,
415 __u32 targ_id)
416 {
417 const struct btf_type *local_type, *targ_type;
418
419 recur:
420 local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
421 targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
422 if (!local_type || !targ_type)
423 return -EINVAL;
424
425 if (btf_is_composite(local_type) && btf_is_composite(targ_type))
426 return 1;
427 if (!btf_kind_core_compat(local_type, targ_type))
428 return 0;
429
430 switch (btf_kind(local_type)) {
431 case BTF_KIND_PTR:
432 case BTF_KIND_FLOAT:
433 return 1;
434 case BTF_KIND_FWD:
435 case BTF_KIND_ENUM64:
436 case BTF_KIND_ENUM: {
437 const char *local_name, *targ_name;
438 size_t local_len, targ_len;
439
440 local_name = btf__name_by_offset(local_btf,
441 local_type->name_off);
442 targ_name = btf__name_by_offset(targ_btf, targ_type->name_off);
443 local_len = bpf_core_essential_name_len(local_name);
444 targ_len = bpf_core_essential_name_len(targ_name);
445 /* one of them is anonymous or both w/ same flavor-less names */
446 return local_len == 0 || targ_len == 0 ||
447 (local_len == targ_len &&
448 strncmp(local_name, targ_name, local_len) == 0);
449 }
450 case BTF_KIND_INT:
451 /* just reject deprecated bitfield-like integers; all other
452 * integers are by default compatible between each other
453 */
454 return btf_int_offset(local_type) == 0 &&
455 btf_int_offset(targ_type) == 0;
456 case BTF_KIND_ARRAY:
457 local_id = btf_array(local_type)->type;
458 targ_id = btf_array(targ_type)->type;
459 goto recur;
460 default:
461 return 0;
462 }
463 }
464
465 /*
466 * Given single high-level named field accessor in local type, find
467 * corresponding high-level accessor for a target type. Along the way,
468 * maintain low-level spec for target as well. Also keep updating target
469 * bit offset.
470 *
471 * Searching is performed through recursive exhaustive enumeration of all
472 * fields of a struct/union. If there are any anonymous (embedded)
473 * structs/unions, they are recursively searched as well. If field with
474 * desired name is found, check compatibility between local and target types,
475 * before returning result.
476 *
477 * 1 is returned, if field is found.
478 * 0 is returned if no compatible field is found.
479 * <0 is returned on error.
480 */
bpf_core_match_member(const struct btf * local_btf,const struct bpf_core_accessor * local_acc,const struct btf * targ_btf,__u32 targ_id,struct bpf_core_spec * spec,__u32 * next_targ_id)481 static int bpf_core_match_member(const struct btf *local_btf,
482 const struct bpf_core_accessor *local_acc,
483 const struct btf *targ_btf,
484 __u32 targ_id,
485 struct bpf_core_spec *spec,
486 __u32 *next_targ_id)
487 {
488 const struct btf_type *local_type, *targ_type;
489 const struct btf_member *local_member, *m;
490 const char *local_name, *targ_name;
491 __u32 local_id;
492 int i, n, found;
493
494 targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
495 if (!targ_type)
496 return -EINVAL;
497 if (!btf_is_composite(targ_type))
498 return 0;
499
500 local_id = local_acc->type_id;
501 local_type = btf_type_by_id(local_btf, local_id);
502 local_member = btf_members(local_type) + local_acc->idx;
503 local_name = btf__name_by_offset(local_btf, local_member->name_off);
504
505 n = btf_vlen(targ_type);
506 m = btf_members(targ_type);
507 for (i = 0; i < n; i++, m++) {
508 __u32 bit_offset;
509
510 bit_offset = btf_member_bit_offset(targ_type, i);
511
512 /* too deep struct/union/array nesting */
513 if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
514 return -E2BIG;
515
516 /* speculate this member will be the good one */
517 spec->bit_offset += bit_offset;
518 spec->raw_spec[spec->raw_len++] = i;
519
520 targ_name = btf__name_by_offset(targ_btf, m->name_off);
521 if (str_is_empty(targ_name)) {
522 /* embedded struct/union, we need to go deeper */
523 found = bpf_core_match_member(local_btf, local_acc,
524 targ_btf, m->type,
525 spec, next_targ_id);
526 if (found) /* either found or error */
527 return found;
528 } else if (strcmp(local_name, targ_name) == 0) {
529 /* matching named field */
530 struct bpf_core_accessor *targ_acc;
531
532 targ_acc = &spec->spec[spec->len++];
533 targ_acc->type_id = targ_id;
534 targ_acc->idx = i;
535 targ_acc->name = targ_name;
536
537 *next_targ_id = m->type;
538 found = bpf_core_fields_are_compat(local_btf,
539 local_member->type,
540 targ_btf, m->type);
541 if (!found)
542 spec->len--; /* pop accessor */
543 return found;
544 }
545 /* member turned out not to be what we looked for */
546 spec->bit_offset -= bit_offset;
547 spec->raw_len--;
548 }
549
550 return 0;
551 }
552
553 /*
554 * Try to match local spec to a target type and, if successful, produce full
555 * target spec (high-level, low-level + bit offset).
556 */
bpf_core_spec_match(struct bpf_core_spec * local_spec,const struct btf * targ_btf,__u32 targ_id,struct bpf_core_spec * targ_spec)557 static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
558 const struct btf *targ_btf, __u32 targ_id,
559 struct bpf_core_spec *targ_spec)
560 {
561 const struct btf_type *targ_type;
562 const struct bpf_core_accessor *local_acc;
563 struct bpf_core_accessor *targ_acc;
564 int i, sz, matched;
565 __u32 name_off;
566
567 memset(targ_spec, 0, sizeof(*targ_spec));
568 targ_spec->btf = targ_btf;
569 targ_spec->root_type_id = targ_id;
570 targ_spec->relo_kind = local_spec->relo_kind;
571
572 if (core_relo_is_type_based(local_spec->relo_kind)) {
573 if (local_spec->relo_kind == BPF_CORE_TYPE_MATCHES)
574 return bpf_core_types_match(local_spec->btf,
575 local_spec->root_type_id,
576 targ_btf, targ_id);
577 else
578 return bpf_core_types_are_compat(local_spec->btf,
579 local_spec->root_type_id,
580 targ_btf, targ_id);
581 }
582
583 local_acc = &local_spec->spec[0];
584 targ_acc = &targ_spec->spec[0];
585
586 if (core_relo_is_enumval_based(local_spec->relo_kind)) {
587 size_t local_essent_len, targ_essent_len;
588 const char *targ_name;
589
590 /* has to resolve to an enum */
591 targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id, &targ_id);
592 if (!btf_is_any_enum(targ_type))
593 return 0;
594
595 local_essent_len = bpf_core_essential_name_len(local_acc->name);
596
597 for (i = 0; i < btf_vlen(targ_type); i++) {
598 if (btf_is_enum(targ_type))
599 name_off = btf_enum(targ_type)[i].name_off;
600 else
601 name_off = btf_enum64(targ_type)[i].name_off;
602
603 targ_name = btf__name_by_offset(targ_spec->btf, name_off);
604 targ_essent_len = bpf_core_essential_name_len(targ_name);
605 if (targ_essent_len != local_essent_len)
606 continue;
607 if (strncmp(local_acc->name, targ_name, local_essent_len) == 0) {
608 targ_acc->type_id = targ_id;
609 targ_acc->idx = i;
610 targ_acc->name = targ_name;
611 targ_spec->len++;
612 targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
613 targ_spec->raw_len++;
614 return 1;
615 }
616 }
617 return 0;
618 }
619
620 if (!core_relo_is_field_based(local_spec->relo_kind))
621 return -EINVAL;
622
623 for (i = 0; i < local_spec->len; i++, local_acc++, targ_acc++) {
624 targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id,
625 &targ_id);
626 if (!targ_type)
627 return -EINVAL;
628
629 if (local_acc->name) {
630 matched = bpf_core_match_member(local_spec->btf,
631 local_acc,
632 targ_btf, targ_id,
633 targ_spec, &targ_id);
634 if (matched <= 0)
635 return matched;
636 } else {
637 /* for i=0, targ_id is already treated as array element
638 * type (because it's the original struct), for others
639 * we should find array element type first
640 */
641 if (i > 0) {
642 const struct btf_array *a;
643 bool flex;
644
645 if (!btf_is_array(targ_type))
646 return 0;
647
648 a = btf_array(targ_type);
649 flex = is_flex_arr(targ_btf, targ_acc - 1, a);
650 if (!flex && local_acc->idx >= a->nelems)
651 return 0;
652 if (!skip_mods_and_typedefs(targ_btf, a->type,
653 &targ_id))
654 return -EINVAL;
655 }
656
657 /* too deep struct/union/array nesting */
658 if (targ_spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
659 return -E2BIG;
660
661 targ_acc->type_id = targ_id;
662 targ_acc->idx = local_acc->idx;
663 targ_acc->name = NULL;
664 targ_spec->len++;
665 targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
666 targ_spec->raw_len++;
667
668 sz = btf__resolve_size(targ_btf, targ_id);
669 if (sz < 0)
670 return sz;
671 targ_spec->bit_offset += local_acc->idx * sz * 8;
672 }
673 }
674
675 return 1;
676 }
677
bpf_core_calc_field_relo(const char * prog_name,const struct bpf_core_relo * relo,const struct bpf_core_spec * spec,__u64 * val,__u32 * field_sz,__u32 * type_id,bool * validate)678 static int bpf_core_calc_field_relo(const char *prog_name,
679 const struct bpf_core_relo *relo,
680 const struct bpf_core_spec *spec,
681 __u64 *val, __u32 *field_sz, __u32 *type_id,
682 bool *validate)
683 {
684 const struct bpf_core_accessor *acc;
685 const struct btf_type *t;
686 __u32 byte_off, byte_sz, bit_off, bit_sz, field_type_id;
687 const struct btf_member *m;
688 const struct btf_type *mt;
689 bool bitfield;
690 __s64 sz;
691
692 *field_sz = 0;
693
694 if (relo->kind == BPF_CORE_FIELD_EXISTS) {
695 *val = spec ? 1 : 0;
696 return 0;
697 }
698
699 if (!spec)
700 return -EUCLEAN; /* request instruction poisoning */
701
702 acc = &spec->spec[spec->len - 1];
703 t = btf_type_by_id(spec->btf, acc->type_id);
704
705 /* a[n] accessor needs special handling */
706 if (!acc->name) {
707 if (relo->kind == BPF_CORE_FIELD_BYTE_OFFSET) {
708 *val = spec->bit_offset / 8;
709 /* remember field size for load/store mem size */
710 sz = btf__resolve_size(spec->btf, acc->type_id);
711 if (sz < 0)
712 return -EINVAL;
713 *field_sz = sz;
714 *type_id = acc->type_id;
715 } else if (relo->kind == BPF_CORE_FIELD_BYTE_SIZE) {
716 sz = btf__resolve_size(spec->btf, acc->type_id);
717 if (sz < 0)
718 return -EINVAL;
719 *val = sz;
720 } else {
721 pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access\n",
722 prog_name, relo->kind, relo->insn_off / 8);
723 return -EINVAL;
724 }
725 if (validate)
726 *validate = true;
727 return 0;
728 }
729
730 m = btf_members(t) + acc->idx;
731 mt = skip_mods_and_typedefs(spec->btf, m->type, &field_type_id);
732 bit_off = spec->bit_offset;
733 bit_sz = btf_member_bitfield_size(t, acc->idx);
734
735 bitfield = bit_sz > 0;
736 if (bitfield) {
737 byte_sz = mt->size;
738 byte_off = bit_off / 8 / byte_sz * byte_sz;
739 /* figure out smallest int size necessary for bitfield load */
740 while (bit_off + bit_sz - byte_off * 8 > byte_sz * 8) {
741 if (byte_sz >= 8) {
742 /* bitfield can't be read with 64-bit read */
743 pr_warn("prog '%s': relo %d at insn #%d can't be satisfied for bitfield\n",
744 prog_name, relo->kind, relo->insn_off / 8);
745 return -E2BIG;
746 }
747 byte_sz *= 2;
748 byte_off = bit_off / 8 / byte_sz * byte_sz;
749 }
750 } else {
751 sz = btf__resolve_size(spec->btf, field_type_id);
752 if (sz < 0)
753 return -EINVAL;
754 byte_sz = sz;
755 byte_off = spec->bit_offset / 8;
756 bit_sz = byte_sz * 8;
757 }
758
759 /* for bitfields, all the relocatable aspects are ambiguous and we
760 * might disagree with compiler, so turn off validation of expected
761 * value, except for signedness
762 */
763 if (validate)
764 *validate = !bitfield;
765
766 switch (relo->kind) {
767 case BPF_CORE_FIELD_BYTE_OFFSET:
768 *val = byte_off;
769 if (!bitfield) {
770 *field_sz = byte_sz;
771 *type_id = field_type_id;
772 }
773 break;
774 case BPF_CORE_FIELD_BYTE_SIZE:
775 *val = byte_sz;
776 break;
777 case BPF_CORE_FIELD_SIGNED:
778 *val = (btf_is_any_enum(mt) && BTF_INFO_KFLAG(mt->info)) ||
779 (btf_int_encoding(mt) & BTF_INT_SIGNED);
780 if (validate)
781 *validate = true; /* signedness is never ambiguous */
782 break;
783 case BPF_CORE_FIELD_LSHIFT_U64:
784 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
785 *val = 64 - (bit_off + bit_sz - byte_off * 8);
786 #else
787 *val = (8 - byte_sz) * 8 + (bit_off - byte_off * 8);
788 #endif
789 break;
790 case BPF_CORE_FIELD_RSHIFT_U64:
791 *val = 64 - bit_sz;
792 if (validate)
793 *validate = true; /* right shift is never ambiguous */
794 break;
795 case BPF_CORE_FIELD_EXISTS:
796 default:
797 return -EOPNOTSUPP;
798 }
799
800 return 0;
801 }
802
bpf_core_calc_type_relo(const struct bpf_core_relo * relo,const struct bpf_core_spec * spec,__u64 * val,bool * validate)803 static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo,
804 const struct bpf_core_spec *spec,
805 __u64 *val, bool *validate)
806 {
807 __s64 sz;
808
809 /* by default, always check expected value in bpf_insn */
810 if (validate)
811 *validate = true;
812
813 /* type-based relos return zero when target type is not found */
814 if (!spec) {
815 *val = 0;
816 return 0;
817 }
818
819 switch (relo->kind) {
820 case BPF_CORE_TYPE_ID_TARGET:
821 *val = spec->root_type_id;
822 /* type ID, embedded in bpf_insn, might change during linking,
823 * so enforcing it is pointless
824 */
825 if (validate)
826 *validate = false;
827 break;
828 case BPF_CORE_TYPE_EXISTS:
829 case BPF_CORE_TYPE_MATCHES:
830 *val = 1;
831 break;
832 case BPF_CORE_TYPE_SIZE:
833 sz = btf__resolve_size(spec->btf, spec->root_type_id);
834 if (sz < 0)
835 return -EINVAL;
836 *val = sz;
837 break;
838 case BPF_CORE_TYPE_ID_LOCAL:
839 /* BPF_CORE_TYPE_ID_LOCAL is handled specially and shouldn't get here */
840 default:
841 return -EOPNOTSUPP;
842 }
843
844 return 0;
845 }
846
bpf_core_calc_enumval_relo(const struct bpf_core_relo * relo,const struct bpf_core_spec * spec,__u64 * val)847 static int bpf_core_calc_enumval_relo(const struct bpf_core_relo *relo,
848 const struct bpf_core_spec *spec,
849 __u64 *val)
850 {
851 const struct btf_type *t;
852
853 switch (relo->kind) {
854 case BPF_CORE_ENUMVAL_EXISTS:
855 *val = spec ? 1 : 0;
856 break;
857 case BPF_CORE_ENUMVAL_VALUE:
858 if (!spec)
859 return -EUCLEAN; /* request instruction poisoning */
860 t = btf_type_by_id(spec->btf, spec->spec[0].type_id);
861 if (btf_is_enum(t))
862 *val = btf_enum(t)[spec->spec[0].idx].val;
863 else
864 *val = btf_enum64_value(btf_enum64(t) + spec->spec[0].idx);
865 break;
866 default:
867 return -EOPNOTSUPP;
868 }
869
870 return 0;
871 }
872
873 /* Calculate original and target relocation values, given local and target
874 * specs and relocation kind. These values are calculated for each candidate.
875 * If there are multiple candidates, resulting values should all be consistent
876 * with each other. Otherwise, libbpf will refuse to proceed due to ambiguity.
877 * If instruction has to be poisoned, *poison will be set to true.
878 */
bpf_core_calc_relo(const char * prog_name,const struct bpf_core_relo * relo,int relo_idx,const struct bpf_core_spec * local_spec,const struct bpf_core_spec * targ_spec,struct bpf_core_relo_res * res)879 static int bpf_core_calc_relo(const char *prog_name,
880 const struct bpf_core_relo *relo,
881 int relo_idx,
882 const struct bpf_core_spec *local_spec,
883 const struct bpf_core_spec *targ_spec,
884 struct bpf_core_relo_res *res)
885 {
886 int err = -EOPNOTSUPP;
887
888 res->orig_val = 0;
889 res->new_val = 0;
890 res->poison = false;
891 res->validate = true;
892 res->fail_memsz_adjust = false;
893 res->orig_sz = res->new_sz = 0;
894 res->orig_type_id = res->new_type_id = 0;
895
896 if (core_relo_is_field_based(relo->kind)) {
897 err = bpf_core_calc_field_relo(prog_name, relo, local_spec,
898 &res->orig_val, &res->orig_sz,
899 &res->orig_type_id, &res->validate);
900 err = err ?: bpf_core_calc_field_relo(prog_name, relo, targ_spec,
901 &res->new_val, &res->new_sz,
902 &res->new_type_id, NULL);
903 if (err)
904 goto done;
905 /* Validate if it's safe to adjust load/store memory size.
906 * Adjustments are performed only if original and new memory
907 * sizes differ.
908 */
909 res->fail_memsz_adjust = false;
910 if (res->orig_sz != res->new_sz) {
911 const struct btf_type *orig_t, *new_t;
912
913 orig_t = btf_type_by_id(local_spec->btf, res->orig_type_id);
914 new_t = btf_type_by_id(targ_spec->btf, res->new_type_id);
915
916 /* There are two use cases in which it's safe to
917 * adjust load/store's mem size:
918 * - reading a 32-bit kernel pointer, while on BPF
919 * size pointers are always 64-bit; in this case
920 * it's safe to "downsize" instruction size due to
921 * pointer being treated as unsigned integer with
922 * zero-extended upper 32-bits;
923 * - reading unsigned integers, again due to
924 * zero-extension is preserving the value correctly.
925 *
926 * In all other cases it's incorrect to attempt to
927 * load/store field because read value will be
928 * incorrect, so we poison relocated instruction.
929 */
930 if (btf_is_ptr(orig_t) && btf_is_ptr(new_t))
931 goto done;
932 if (btf_is_int(orig_t) && btf_is_int(new_t) &&
933 btf_int_encoding(orig_t) != BTF_INT_SIGNED &&
934 btf_int_encoding(new_t) != BTF_INT_SIGNED)
935 goto done;
936
937 /* mark as invalid mem size adjustment, but this will
938 * only be checked for LDX/STX/ST insns
939 */
940 res->fail_memsz_adjust = true;
941 }
942 } else if (core_relo_is_type_based(relo->kind)) {
943 err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val, &res->validate);
944 err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val, NULL);
945 } else if (core_relo_is_enumval_based(relo->kind)) {
946 err = bpf_core_calc_enumval_relo(relo, local_spec, &res->orig_val);
947 err = err ?: bpf_core_calc_enumval_relo(relo, targ_spec, &res->new_val);
948 }
949
950 done:
951 if (err == -EUCLEAN) {
952 /* EUCLEAN is used to signal instruction poisoning request */
953 res->poison = true;
954 err = 0;
955 } else if (err == -EOPNOTSUPP) {
956 /* EOPNOTSUPP means unknown/unsupported relocation */
957 pr_warn("prog '%s': relo #%d: unrecognized CO-RE relocation %s (%d) at insn #%d\n",
958 prog_name, relo_idx, core_relo_kind_str(relo->kind),
959 relo->kind, relo->insn_off / 8);
960 }
961
962 return err;
963 }
964
965 /*
966 * Turn instruction for which CO_RE relocation failed into invalid one with
967 * distinct signature.
968 */
bpf_core_poison_insn(const char * prog_name,int relo_idx,int insn_idx,struct bpf_insn * insn)969 static void bpf_core_poison_insn(const char *prog_name, int relo_idx,
970 int insn_idx, struct bpf_insn *insn)
971 {
972 pr_debug("prog '%s': relo #%d: substituting insn #%d w/ invalid insn\n",
973 prog_name, relo_idx, insn_idx);
974 insn->code = BPF_JMP | BPF_CALL;
975 insn->dst_reg = 0;
976 insn->src_reg = 0;
977 insn->off = 0;
978 /* if this instruction is reachable (not a dead code),
979 * verifier will complain with the following message:
980 * invalid func unknown#195896080
981 */
982 insn->imm = 195896080; /* => 0xbad2310 => "bad relo" */
983 }
984
insn_bpf_size_to_bytes(struct bpf_insn * insn)985 static int insn_bpf_size_to_bytes(struct bpf_insn *insn)
986 {
987 switch (BPF_SIZE(insn->code)) {
988 case BPF_DW: return 8;
989 case BPF_W: return 4;
990 case BPF_H: return 2;
991 case BPF_B: return 1;
992 default: return -1;
993 }
994 }
995
insn_bytes_to_bpf_size(__u32 sz)996 static int insn_bytes_to_bpf_size(__u32 sz)
997 {
998 switch (sz) {
999 case 8: return BPF_DW;
1000 case 4: return BPF_W;
1001 case 2: return BPF_H;
1002 case 1: return BPF_B;
1003 default: return -1;
1004 }
1005 }
1006
1007 /*
1008 * Patch relocatable BPF instruction.
1009 *
1010 * Patched value is determined by relocation kind and target specification.
1011 * For existence relocations target spec will be NULL if field/type is not found.
1012 * Expected insn->imm value is determined using relocation kind and local
1013 * spec, and is checked before patching instruction. If actual insn->imm value
1014 * is wrong, bail out with error.
1015 *
1016 * Currently supported classes of BPF instruction are:
1017 * 1. rX = <imm> (assignment with immediate operand);
1018 * 2. rX += <imm> (arithmetic operations with immediate operand);
1019 * 3. rX = <imm64> (load with 64-bit immediate value);
1020 * 4. rX = *(T *)(rY + <off>), where T is one of {u8, u16, u32, u64};
1021 * 5. *(T *)(rX + <off>) = rY, where T is one of {u8, u16, u32, u64};
1022 * 6. *(T *)(rX + <off>) = <imm>, where T is one of {u8, u16, u32, u64}.
1023 */
bpf_core_patch_insn(const char * prog_name,struct bpf_insn * insn,int insn_idx,const struct bpf_core_relo * relo,int relo_idx,const struct bpf_core_relo_res * res)1024 int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
1025 int insn_idx, const struct bpf_core_relo *relo,
1026 int relo_idx, const struct bpf_core_relo_res *res)
1027 {
1028 __u64 orig_val, new_val;
1029 __u8 class;
1030
1031 class = BPF_CLASS(insn->code);
1032
1033 if (res->poison) {
1034 poison:
1035 /* poison second part of ldimm64 to avoid confusing error from
1036 * verifier about "unknown opcode 00"
1037 */
1038 if (is_ldimm64_insn(insn))
1039 bpf_core_poison_insn(prog_name, relo_idx, insn_idx + 1, insn + 1);
1040 bpf_core_poison_insn(prog_name, relo_idx, insn_idx, insn);
1041 return 0;
1042 }
1043
1044 orig_val = res->orig_val;
1045 new_val = res->new_val;
1046
1047 switch (class) {
1048 case BPF_ALU:
1049 case BPF_ALU64:
1050 if (BPF_SRC(insn->code) != BPF_K)
1051 return -EINVAL;
1052 if (res->validate && insn->imm != orig_val) {
1053 pr_warn("prog '%s': relo #%d: unexpected insn #%d (ALU/ALU64) value: got %u, exp %llu -> %llu\n",
1054 prog_name, relo_idx,
1055 insn_idx, insn->imm, (unsigned long long)orig_val,
1056 (unsigned long long)new_val);
1057 return -EINVAL;
1058 }
1059 orig_val = insn->imm;
1060 insn->imm = new_val;
1061 pr_debug("prog '%s': relo #%d: patched insn #%d (ALU/ALU64) imm %llu -> %llu\n",
1062 prog_name, relo_idx, insn_idx,
1063 (unsigned long long)orig_val, (unsigned long long)new_val);
1064 break;
1065 case BPF_LDX:
1066 case BPF_ST:
1067 case BPF_STX:
1068 if (res->validate && insn->off != orig_val) {
1069 pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDX/ST/STX) value: got %u, exp %llu -> %llu\n",
1070 prog_name, relo_idx, insn_idx, insn->off, (unsigned long long)orig_val,
1071 (unsigned long long)new_val);
1072 return -EINVAL;
1073 }
1074 if (new_val > SHRT_MAX) {
1075 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) value too big: %llu\n",
1076 prog_name, relo_idx, insn_idx, (unsigned long long)new_val);
1077 return -ERANGE;
1078 }
1079 if (res->fail_memsz_adjust) {
1080 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) accesses field incorrectly. "
1081 "Make sure you are accessing pointers, unsigned integers, or fields of matching type and size.\n",
1082 prog_name, relo_idx, insn_idx);
1083 goto poison;
1084 }
1085
1086 orig_val = insn->off;
1087 insn->off = new_val;
1088 pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) off %llu -> %llu\n",
1089 prog_name, relo_idx, insn_idx, (unsigned long long)orig_val,
1090 (unsigned long long)new_val);
1091
1092 if (res->new_sz != res->orig_sz) {
1093 int insn_bytes_sz, insn_bpf_sz;
1094
1095 insn_bytes_sz = insn_bpf_size_to_bytes(insn);
1096 if (insn_bytes_sz != res->orig_sz) {
1097 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) unexpected mem size: got %d, exp %u\n",
1098 prog_name, relo_idx, insn_idx, insn_bytes_sz, res->orig_sz);
1099 return -EINVAL;
1100 }
1101
1102 insn_bpf_sz = insn_bytes_to_bpf_size(res->new_sz);
1103 if (insn_bpf_sz < 0) {
1104 pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) invalid new mem size: %u\n",
1105 prog_name, relo_idx, insn_idx, res->new_sz);
1106 return -EINVAL;
1107 }
1108
1109 insn->code = BPF_MODE(insn->code) | insn_bpf_sz | BPF_CLASS(insn->code);
1110 pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) mem_sz %u -> %u\n",
1111 prog_name, relo_idx, insn_idx, res->orig_sz, res->new_sz);
1112 }
1113 break;
1114 case BPF_LD: {
1115 __u64 imm;
1116
1117 if (!is_ldimm64_insn(insn) ||
1118 insn[0].src_reg != 0 || insn[0].off != 0 ||
1119 insn[1].code != 0 || insn[1].dst_reg != 0 ||
1120 insn[1].src_reg != 0 || insn[1].off != 0) {
1121 pr_warn("prog '%s': relo #%d: insn #%d (LDIMM64) has unexpected form\n",
1122 prog_name, relo_idx, insn_idx);
1123 return -EINVAL;
1124 }
1125
1126 imm = (__u32)insn[0].imm | ((__u64)insn[1].imm << 32);
1127 if (res->validate && imm != orig_val) {
1128 pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %llu -> %llu\n",
1129 prog_name, relo_idx,
1130 insn_idx, (unsigned long long)imm,
1131 (unsigned long long)orig_val, (unsigned long long)new_val);
1132 return -EINVAL;
1133 }
1134
1135 insn[0].imm = new_val;
1136 insn[1].imm = new_val >> 32;
1137 pr_debug("prog '%s': relo #%d: patched insn #%d (LDIMM64) imm64 %llu -> %llu\n",
1138 prog_name, relo_idx, insn_idx,
1139 (unsigned long long)imm, (unsigned long long)new_val);
1140 break;
1141 }
1142 default:
1143 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",
1144 prog_name, relo_idx, insn_idx, insn->code,
1145 insn->src_reg, insn->dst_reg, insn->off, insn->imm);
1146 return -EINVAL;
1147 }
1148
1149 return 0;
1150 }
1151
1152 /* Output spec definition in the format:
1153 * [<type-id>] (<type-name>) + <raw-spec> => <offset>@<spec>,
1154 * where <spec> is a C-syntax view of recorded field access, e.g.: x.a[3].b
1155 */
bpf_core_format_spec(char * buf,size_t buf_sz,const struct bpf_core_spec * spec)1156 int bpf_core_format_spec(char *buf, size_t buf_sz, const struct bpf_core_spec *spec)
1157 {
1158 const struct btf_type *t;
1159 const char *s;
1160 __u32 type_id;
1161 int i, len = 0;
1162
1163 #define append_buf(fmt, args...) \
1164 ({ \
1165 int r; \
1166 r = snprintf(buf, buf_sz, fmt, ##args); \
1167 len += r; \
1168 if (r >= buf_sz) \
1169 r = buf_sz; \
1170 buf += r; \
1171 buf_sz -= r; \
1172 })
1173
1174 type_id = spec->root_type_id;
1175 t = btf_type_by_id(spec->btf, type_id);
1176 s = btf__name_by_offset(spec->btf, t->name_off);
1177
1178 append_buf("<%s> [%u] %s %s",
1179 core_relo_kind_str(spec->relo_kind),
1180 type_id, btf_kind_str(t), str_is_empty(s) ? "<anon>" : s);
1181
1182 if (core_relo_is_type_based(spec->relo_kind))
1183 return len;
1184
1185 if (core_relo_is_enumval_based(spec->relo_kind)) {
1186 t = skip_mods_and_typedefs(spec->btf, type_id, NULL);
1187 if (btf_is_enum(t)) {
1188 const struct btf_enum *e;
1189 const char *fmt_str;
1190
1191 e = btf_enum(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 = %d" : "::%s = %u";
1194 append_buf(fmt_str, s, e->val);
1195 } else {
1196 const struct btf_enum64 *e;
1197 const char *fmt_str;
1198
1199 e = btf_enum64(t) + spec->raw_spec[0];
1200 s = btf__name_by_offset(spec->btf, e->name_off);
1201 fmt_str = BTF_INFO_KFLAG(t->info) ? "::%s = %lld" : "::%s = %llu";
1202 append_buf(fmt_str, s, (unsigned long long)btf_enum64_value(e));
1203 }
1204 return len;
1205 }
1206
1207 if (core_relo_is_field_based(spec->relo_kind)) {
1208 for (i = 0; i < spec->len; i++) {
1209 if (spec->spec[i].name)
1210 append_buf(".%s", spec->spec[i].name);
1211 else if (i > 0 || spec->spec[i].idx > 0)
1212 append_buf("[%u]", spec->spec[i].idx);
1213 }
1214
1215 append_buf(" (");
1216 for (i = 0; i < spec->raw_len; i++)
1217 append_buf("%s%d", i == 0 ? "" : ":", spec->raw_spec[i]);
1218
1219 if (spec->bit_offset % 8)
1220 append_buf(" @ offset %u.%u)", spec->bit_offset / 8, spec->bit_offset % 8);
1221 else
1222 append_buf(" @ offset %u)", spec->bit_offset / 8);
1223 return len;
1224 }
1225
1226 return len;
1227 #undef append_buf
1228 }
1229
1230 /*
1231 * Calculate CO-RE relocation target result.
1232 *
1233 * The outline and important points of the algorithm:
1234 * 1. For given local type, find corresponding candidate target types.
1235 * Candidate type is a type with the same "essential" name, ignoring
1236 * everything after last triple underscore (___). E.g., `sample`,
1237 * `sample___flavor_one`, `sample___flavor_another_one`, are all candidates
1238 * for each other. Names with triple underscore are referred to as
1239 * "flavors" and are useful, among other things, to allow to
1240 * specify/support incompatible variations of the same kernel struct, which
1241 * might differ between different kernel versions and/or build
1242 * configurations.
1243 *
1244 * N.B. Struct "flavors" could be generated by bpftool's BTF-to-C
1245 * converter, when deduplicated BTF of a kernel still contains more than
1246 * one different types with the same name. In that case, ___2, ___3, etc
1247 * are appended starting from second name conflict. But start flavors are
1248 * also useful to be defined "locally", in BPF program, to extract same
1249 * data from incompatible changes between different kernel
1250 * versions/configurations. For instance, to handle field renames between
1251 * kernel versions, one can use two flavors of the struct name with the
1252 * same common name and use conditional relocations to extract that field,
1253 * depending on target kernel version.
1254 * 2. For each candidate type, try to match local specification to this
1255 * candidate target type. Matching involves finding corresponding
1256 * high-level spec accessors, meaning that all named fields should match,
1257 * as well as all array accesses should be within the actual bounds. Also,
1258 * types should be compatible (see bpf_core_fields_are_compat for details).
1259 * 3. It is supported and expected that there might be multiple flavors
1260 * matching the spec. As long as all the specs resolve to the same set of
1261 * offsets across all candidates, there is no error. If there is any
1262 * ambiguity, CO-RE relocation will fail. This is necessary to accommodate
1263 * imperfection of BTF deduplication, which can cause slight duplication of
1264 * the same BTF type, if some directly or indirectly referenced (by
1265 * pointer) type gets resolved to different actual types in different
1266 * object files. If such a situation occurs, deduplicated BTF will end up
1267 * with two (or more) structurally identical types, which differ only in
1268 * types they refer to through pointer. This should be OK in most cases and
1269 * is not an error.
1270 * 4. Candidate types search is performed by linearly scanning through all
1271 * types in target BTF. It is anticipated that this is overall more
1272 * efficient memory-wise and not significantly worse (if not better)
1273 * CPU-wise compared to prebuilding a map from all local type names to
1274 * a list of candidate type names. It's also sped up by caching resolved
1275 * list of matching candidates per each local "root" type ID, that has at
1276 * least one bpf_core_relo associated with it. This list is shared
1277 * between multiple relocations for the same type ID and is updated as some
1278 * of the candidates are pruned due to structural incompatibility.
1279 */
bpf_core_calc_relo_insn(const char * prog_name,const struct bpf_core_relo * relo,int relo_idx,const struct btf * local_btf,struct bpf_core_cand_list * cands,struct bpf_core_spec * specs_scratch,struct bpf_core_relo_res * targ_res)1280 int bpf_core_calc_relo_insn(const char *prog_name,
1281 const struct bpf_core_relo *relo,
1282 int relo_idx,
1283 const struct btf *local_btf,
1284 struct bpf_core_cand_list *cands,
1285 struct bpf_core_spec *specs_scratch,
1286 struct bpf_core_relo_res *targ_res)
1287 {
1288 struct bpf_core_spec *local_spec = &specs_scratch[0];
1289 struct bpf_core_spec *cand_spec = &specs_scratch[1];
1290 struct bpf_core_spec *targ_spec = &specs_scratch[2];
1291 struct bpf_core_relo_res cand_res;
1292 const struct btf_type *local_type;
1293 const char *local_name;
1294 __u32 local_id;
1295 char spec_buf[256];
1296 int i, j, err;
1297
1298 local_id = relo->type_id;
1299 local_type = btf_type_by_id(local_btf, local_id);
1300 local_name = btf__name_by_offset(local_btf, local_type->name_off);
1301 if (!local_name)
1302 return -EINVAL;
1303
1304 err = bpf_core_parse_spec(prog_name, local_btf, relo, local_spec);
1305 if (err) {
1306 const char *spec_str;
1307
1308 spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
1309 pr_warn("prog '%s': relo #%d: parsing [%d] %s %s + %s failed: %d\n",
1310 prog_name, relo_idx, local_id, btf_kind_str(local_type),
1311 str_is_empty(local_name) ? "<anon>" : local_name,
1312 spec_str ?: "<?>", err);
1313 return -EINVAL;
1314 }
1315
1316 bpf_core_format_spec(spec_buf, sizeof(spec_buf), local_spec);
1317 pr_debug("prog '%s': relo #%d: %s\n", prog_name, relo_idx, spec_buf);
1318
1319 /* TYPE_ID_LOCAL relo is special and doesn't need candidate search */
1320 if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) {
1321 /* bpf_insn's imm value could get out of sync during linking */
1322 memset(targ_res, 0, sizeof(*targ_res));
1323 targ_res->validate = false;
1324 targ_res->poison = false;
1325 targ_res->orig_val = local_spec->root_type_id;
1326 targ_res->new_val = local_spec->root_type_id;
1327 return 0;
1328 }
1329
1330 /* libbpf doesn't support candidate search for anonymous types */
1331 if (str_is_empty(local_name)) {
1332 pr_warn("prog '%s': relo #%d: <%s> (%d) relocation doesn't support anonymous types\n",
1333 prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind);
1334 return -EOPNOTSUPP;
1335 }
1336
1337 for (i = 0, j = 0; i < cands->len; i++) {
1338 err = bpf_core_spec_match(local_spec, cands->cands[i].btf,
1339 cands->cands[i].id, cand_spec);
1340 if (err < 0) {
1341 bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
1342 pr_warn("prog '%s': relo #%d: error matching candidate #%d %s: %d\n ",
1343 prog_name, relo_idx, i, spec_buf, err);
1344 return err;
1345 }
1346
1347 bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
1348 pr_debug("prog '%s': relo #%d: %s candidate #%d %s\n", prog_name,
1349 relo_idx, err == 0 ? "non-matching" : "matching", i, spec_buf);
1350
1351 if (err == 0)
1352 continue;
1353
1354 err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, cand_spec, &cand_res);
1355 if (err)
1356 return err;
1357
1358 if (j == 0) {
1359 *targ_res = cand_res;
1360 *targ_spec = *cand_spec;
1361 } else if (cand_spec->bit_offset != targ_spec->bit_offset) {
1362 /* if there are many field relo candidates, they
1363 * should all resolve to the same bit offset
1364 */
1365 pr_warn("prog '%s': relo #%d: field offset ambiguity: %u != %u\n",
1366 prog_name, relo_idx, cand_spec->bit_offset,
1367 targ_spec->bit_offset);
1368 return -EINVAL;
1369 } else if (cand_res.poison != targ_res->poison ||
1370 cand_res.new_val != targ_res->new_val) {
1371 /* all candidates should result in the same relocation
1372 * decision and value, otherwise it's dangerous to
1373 * proceed due to ambiguity
1374 */
1375 pr_warn("prog '%s': relo #%d: relocation decision ambiguity: %s %llu != %s %llu\n",
1376 prog_name, relo_idx,
1377 cand_res.poison ? "failure" : "success",
1378 (unsigned long long)cand_res.new_val,
1379 targ_res->poison ? "failure" : "success",
1380 (unsigned long long)targ_res->new_val);
1381 return -EINVAL;
1382 }
1383
1384 cands->cands[j++] = cands->cands[i];
1385 }
1386
1387 /*
1388 * For BPF_CORE_FIELD_EXISTS relo or when used BPF program has field
1389 * existence checks or kernel version/config checks, it's expected
1390 * that we might not find any candidates. In this case, if field
1391 * wasn't found in any candidate, the list of candidates shouldn't
1392 * change at all, we'll just handle relocating appropriately,
1393 * depending on relo's kind.
1394 */
1395 if (j > 0)
1396 cands->len = j;
1397
1398 /*
1399 * If no candidates were found, it might be both a programmer error,
1400 * as well as expected case, depending whether instruction w/
1401 * relocation is guarded in some way that makes it unreachable (dead
1402 * code) if relocation can't be resolved. This is handled in
1403 * bpf_core_patch_insn() uniformly by replacing that instruction with
1404 * BPF helper call insn (using invalid helper ID). If that instruction
1405 * is indeed unreachable, then it will be ignored and eliminated by
1406 * verifier. If it was an error, then verifier will complain and point
1407 * to a specific instruction number in its log.
1408 */
1409 if (j == 0) {
1410 pr_debug("prog '%s': relo #%d: no matching targets found\n",
1411 prog_name, relo_idx);
1412
1413 /* calculate single target relo result explicitly */
1414 err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, NULL, targ_res);
1415 if (err)
1416 return err;
1417 }
1418
1419 return 0;
1420 }
1421
bpf_core_names_match(const struct btf * local_btf,size_t local_name_off,const struct btf * targ_btf,size_t targ_name_off)1422 static bool bpf_core_names_match(const struct btf *local_btf, size_t local_name_off,
1423 const struct btf *targ_btf, size_t targ_name_off)
1424 {
1425 const char *local_n, *targ_n;
1426 size_t local_len, targ_len;
1427
1428 local_n = btf__name_by_offset(local_btf, local_name_off);
1429 targ_n = btf__name_by_offset(targ_btf, targ_name_off);
1430
1431 if (str_is_empty(targ_n))
1432 return str_is_empty(local_n);
1433
1434 targ_len = bpf_core_essential_name_len(targ_n);
1435 local_len = bpf_core_essential_name_len(local_n);
1436
1437 return targ_len == local_len && strncmp(local_n, targ_n, local_len) == 0;
1438 }
1439
bpf_core_enums_match(const struct btf * local_btf,const struct btf_type * local_t,const struct btf * targ_btf,const struct btf_type * targ_t)1440 static int bpf_core_enums_match(const struct btf *local_btf, const struct btf_type *local_t,
1441 const struct btf *targ_btf, const struct btf_type *targ_t)
1442 {
1443 __u16 local_vlen = btf_vlen(local_t);
1444 __u16 targ_vlen = btf_vlen(targ_t);
1445 int i, j;
1446
1447 if (local_t->size != targ_t->size)
1448 return 0;
1449
1450 if (local_vlen > targ_vlen)
1451 return 0;
1452
1453 /* iterate over the local enum's variants and make sure each has
1454 * a symbolic name correspondent in the target
1455 */
1456 for (i = 0; i < local_vlen; i++) {
1457 bool matched = false;
1458 __u32 local_n_off, targ_n_off;
1459
1460 local_n_off = btf_is_enum(local_t) ? btf_enum(local_t)[i].name_off :
1461 btf_enum64(local_t)[i].name_off;
1462
1463 for (j = 0; j < targ_vlen; j++) {
1464 targ_n_off = btf_is_enum(targ_t) ? btf_enum(targ_t)[j].name_off :
1465 btf_enum64(targ_t)[j].name_off;
1466
1467 if (bpf_core_names_match(local_btf, local_n_off, targ_btf, targ_n_off)) {
1468 matched = true;
1469 break;
1470 }
1471 }
1472
1473 if (!matched)
1474 return 0;
1475 }
1476 return 1;
1477 }
1478
bpf_core_composites_match(const struct btf * local_btf,const struct btf_type * local_t,const struct btf * targ_btf,const struct btf_type * targ_t,bool behind_ptr,int level)1479 static int bpf_core_composites_match(const struct btf *local_btf, const struct btf_type *local_t,
1480 const struct btf *targ_btf, const struct btf_type *targ_t,
1481 bool behind_ptr, int level)
1482 {
1483 const struct btf_member *local_m = btf_members(local_t);
1484 __u16 local_vlen = btf_vlen(local_t);
1485 __u16 targ_vlen = btf_vlen(targ_t);
1486 int i, j, err;
1487
1488 if (local_vlen > targ_vlen)
1489 return 0;
1490
1491 /* check that all local members have a match in the target */
1492 for (i = 0; i < local_vlen; i++, local_m++) {
1493 const struct btf_member *targ_m = btf_members(targ_t);
1494 bool matched = false;
1495
1496 for (j = 0; j < targ_vlen; j++, targ_m++) {
1497 if (!bpf_core_names_match(local_btf, local_m->name_off,
1498 targ_btf, targ_m->name_off))
1499 continue;
1500
1501 err = __bpf_core_types_match(local_btf, local_m->type, targ_btf,
1502 targ_m->type, behind_ptr, level - 1);
1503 if (err < 0)
1504 return err;
1505 if (err > 0) {
1506 matched = true;
1507 break;
1508 }
1509 }
1510
1511 if (!matched)
1512 return 0;
1513 }
1514 return 1;
1515 }
1516
1517 /* Check that two types "match". This function assumes that root types were
1518 * already checked for name match.
1519 *
1520 * The matching relation is defined as follows:
1521 * - modifiers and typedefs are stripped (and, hence, effectively ignored)
1522 * - generally speaking types need to be of same kind (struct vs. struct, union
1523 * vs. union, etc.)
1524 * - exceptions are struct/union behind a pointer which could also match a
1525 * forward declaration of a struct or union, respectively, and enum vs.
1526 * enum64 (see below)
1527 * Then, depending on type:
1528 * - integers:
1529 * - match if size and signedness match
1530 * - arrays & pointers:
1531 * - target types are recursively matched
1532 * - structs & unions:
1533 * - local members need to exist in target with the same name
1534 * - for each member we recursively check match unless it is already behind a
1535 * pointer, in which case we only check matching names and compatible kind
1536 * - enums:
1537 * - local variants have to have a match in target by symbolic name (but not
1538 * numeric value)
1539 * - size has to match (but enum may match enum64 and vice versa)
1540 * - function pointers:
1541 * - number and position of arguments in local type has to match target
1542 * - for each argument and the return value we recursively check match
1543 */
__bpf_core_types_match(const struct btf * local_btf,__u32 local_id,const struct btf * targ_btf,__u32 targ_id,bool behind_ptr,int level)1544 int __bpf_core_types_match(const struct btf *local_btf, __u32 local_id, const struct btf *targ_btf,
1545 __u32 targ_id, bool behind_ptr, int level)
1546 {
1547 const struct btf_type *local_t, *targ_t;
1548 int depth = 32; /* max recursion depth */
1549 __u16 local_k, targ_k;
1550
1551 if (level <= 0)
1552 return -EINVAL;
1553
1554 local_t = btf_type_by_id(local_btf, local_id);
1555 targ_t = btf_type_by_id(targ_btf, targ_id);
1556
1557 recur:
1558 depth--;
1559 if (depth < 0)
1560 return -EINVAL;
1561
1562 local_t = skip_mods_and_typedefs(local_btf, local_id, &local_id);
1563 targ_t = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
1564 if (!local_t || !targ_t)
1565 return -EINVAL;
1566
1567 /* While the name check happens after typedefs are skipped, root-level
1568 * typedefs would still be name-matched as that's the contract with
1569 * callers.
1570 */
1571 if (!bpf_core_names_match(local_btf, local_t->name_off, targ_btf, targ_t->name_off))
1572 return 0;
1573
1574 local_k = btf_kind(local_t);
1575 targ_k = btf_kind(targ_t);
1576
1577 switch (local_k) {
1578 case BTF_KIND_UNKN:
1579 return local_k == targ_k;
1580 case BTF_KIND_FWD: {
1581 bool local_f = BTF_INFO_KFLAG(local_t->info);
1582
1583 if (behind_ptr) {
1584 if (local_k == targ_k)
1585 return local_f == BTF_INFO_KFLAG(targ_t->info);
1586
1587 /* for forward declarations kflag dictates whether the
1588 * target is a struct (0) or union (1)
1589 */
1590 return (targ_k == BTF_KIND_STRUCT && !local_f) ||
1591 (targ_k == BTF_KIND_UNION && local_f);
1592 } else {
1593 if (local_k != targ_k)
1594 return 0;
1595
1596 /* match if the forward declaration is for the same kind */
1597 return local_f == BTF_INFO_KFLAG(targ_t->info);
1598 }
1599 }
1600 case BTF_KIND_ENUM:
1601 case BTF_KIND_ENUM64:
1602 if (!btf_is_any_enum(targ_t))
1603 return 0;
1604
1605 return bpf_core_enums_match(local_btf, local_t, targ_btf, targ_t);
1606 case BTF_KIND_STRUCT:
1607 case BTF_KIND_UNION:
1608 if (behind_ptr) {
1609 bool targ_f = BTF_INFO_KFLAG(targ_t->info);
1610
1611 if (local_k == targ_k)
1612 return 1;
1613
1614 if (targ_k != BTF_KIND_FWD)
1615 return 0;
1616
1617 return (local_k == BTF_KIND_UNION) == targ_f;
1618 } else {
1619 if (local_k != targ_k)
1620 return 0;
1621
1622 return bpf_core_composites_match(local_btf, local_t, targ_btf, targ_t,
1623 behind_ptr, level);
1624 }
1625 case BTF_KIND_INT: {
1626 __u8 local_sgn;
1627 __u8 targ_sgn;
1628
1629 if (local_k != targ_k)
1630 return 0;
1631
1632 local_sgn = btf_int_encoding(local_t) & BTF_INT_SIGNED;
1633 targ_sgn = btf_int_encoding(targ_t) & BTF_INT_SIGNED;
1634
1635 return local_t->size == targ_t->size && local_sgn == targ_sgn;
1636 }
1637 case BTF_KIND_PTR:
1638 if (local_k != targ_k)
1639 return 0;
1640
1641 behind_ptr = true;
1642
1643 local_id = local_t->type;
1644 targ_id = targ_t->type;
1645 goto recur;
1646 case BTF_KIND_ARRAY: {
1647 const struct btf_array *local_array = btf_array(local_t);
1648 const struct btf_array *targ_array = btf_array(targ_t);
1649
1650 if (local_k != targ_k)
1651 return 0;
1652
1653 if (local_array->nelems != targ_array->nelems)
1654 return 0;
1655
1656 local_id = local_array->type;
1657 targ_id = targ_array->type;
1658 goto recur;
1659 }
1660 case BTF_KIND_FUNC_PROTO: {
1661 struct btf_param *local_p = btf_params(local_t);
1662 struct btf_param *targ_p = btf_params(targ_t);
1663 __u16 local_vlen = btf_vlen(local_t);
1664 __u16 targ_vlen = btf_vlen(targ_t);
1665 int i, err;
1666
1667 if (local_k != targ_k)
1668 return 0;
1669
1670 if (local_vlen != targ_vlen)
1671 return 0;
1672
1673 for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
1674 err = __bpf_core_types_match(local_btf, local_p->type, targ_btf,
1675 targ_p->type, behind_ptr, level - 1);
1676 if (err <= 0)
1677 return err;
1678 }
1679
1680 /* tail recurse for return type check */
1681 local_id = local_t->type;
1682 targ_id = targ_t->type;
1683 goto recur;
1684 }
1685 default:
1686 pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
1687 btf_kind_str(local_t), local_id, targ_id);
1688 return 0;
1689 }
1690 }
1691