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, type: t, type_size: &size);
39	if (IS_ERR(ptr: t))
40	return PTR_ERR(ptr: 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, type_id: 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_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
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
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
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
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(btf: local_btf, type_id: local_id);
154	targ_type = btf_type_by_id(btf: targ_btf, type_id: targ_id);
155	if (!btf_kind_core_compat(t1: local_type, t2: 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(btf: local_btf, id: local_id, res_id: &local_id);
164	targ_type = skip_mods_and_typedefs(btf: targ_btf, id: targ_id, res_id: &targ_id);
165	if (!local_type || !targ_type)
166	return -EINVAL;
167
168	if (!btf_kind_core_compat(t1: local_type, t2: targ_type))
169	return 0;
170
171	switch (btf_kind(t: 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(t: local_type) == 0 && btf_int_offset(t: 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(t: local_type)->type;
190	targ_id = btf_array(t: targ_type)->type;
191	goto recur;
192	case BTF_KIND_FUNC_PROTO: {
193	struct btf_param *local_p = btf_params(t: local_type);
194	struct btf_param *targ_p = btf_params(t: targ_type);
195	__u16 local_vlen = btf_vlen(t: local_type);
196	__u16 targ_vlen = btf_vlen(t: 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(btf: local_btf, id: local_p->type, res_id: &local_id);
207	skip_mods_and_typedefs(btf: targ_btf, id: targ_p->type, res_id: &targ_id);
208	err = __bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id,
209	level: level - 1);
210	if (err <= 0)
211	return err;
212	}
213
214	/* tail recurse for return type check */
215	skip_mods_and_typedefs(btf: local_btf, id: local_type->type, res_id: &local_id);
216	skip_mods_and_typedefs(btf: targ_btf, id: targ_type->type, res_id: &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	*/
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, offset: relo->access_str_off);
275	if (str_is_empty(s: 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(kind: 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, id: relo->type_id, res_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(kind: 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, offset: name_off);
323	return 0;
324	}
325
326	if (!core_relo_is_field_based(kind: relo->kind))
327	return -EINVAL;
328
329	sz = btf__resolve_size(btf, type_id: 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, res_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, member_idx: 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, offset: m->name_off);
355	if (str_is_empty(s: 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, id: a->type, res_id: &id);
370	if (!t)
371	return -EINVAL;
372
373	flex = is_flex_arr(btf, acc: acc - 1, arr: 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, type_id: 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	*/
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(btf: local_btf, id: local_id, res_id: &local_id);
421	targ_type = skip_mods_and_typedefs(btf: targ_btf, id: targ_id, res_id: &targ_id);
422	if (!local_type || !targ_type)
423	return -EINVAL;
424
425	if (btf_is_composite(t: local_type) && btf_is_composite(t: targ_type))
426	return 1;
427	if (!btf_kind_core_compat(t1: local_type, t2: targ_type))
428	return 0;
429
430	switch (btf_kind(t: 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(btf: local_btf,
441	offset: local_type->name_off);
442	targ_name = btf__name_by_offset(btf: targ_btf, offset: targ_type->name_off);
443	local_len = bpf_core_essential_name_len(name: local_name);
444	targ_len = bpf_core_essential_name_len(name: 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(t: local_type) == 0 &&
455	btf_int_offset(t: targ_type) == 0;
456	case BTF_KIND_ARRAY:
457	local_id = btf_array(t: local_type)->type;
458	targ_id = btf_array(t: 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	*/
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(btf: targ_btf, id: targ_id, res_id: &targ_id);
495	if (!targ_type)
496	return -EINVAL;
497	if (!btf_is_composite(t: targ_type))
498	return 0;
499
500	local_id = local_acc->type_id;
501	local_type = btf_type_by_id(btf: local_btf, type_id: local_id);
502	local_member = btf_members(t: local_type) + local_acc->idx;
503	local_name = btf__name_by_offset(btf: local_btf, offset: local_member->name_off);
504
505	n = btf_vlen(t: targ_type);
506	m = btf_members(t: targ_type);
507	for (i = 0; i < n; i++, m++) {
508	__u32 bit_offset;
509
510	bit_offset = btf_member_bit_offset(t: targ_type, member_idx: 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(btf: targ_btf, offset: m->name_off);
521	if (str_is_empty(s: targ_name)) {
522	/* embedded struct/union, we need to go deeper */
523	found = bpf_core_match_member(local_btf, local_acc,
524	targ_btf, targ_id: 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_id: local_member->type,
540	targ_btf, targ_id: 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	*/
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(kind: local_spec->relo_kind)) {
573	if (local_spec->relo_kind == BPF_CORE_TYPE_MATCHES)
574	return bpf_core_types_match(local_btf: local_spec->btf,
575	local_id: local_spec->root_type_id,
576	targ_btf, targ_id);
577	else
578	return bpf_core_types_are_compat(local_btf: local_spec->btf,
579	local_id: 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(kind: 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(btf: targ_spec->btf, id: targ_id, res_id: &targ_id);
592	if (!btf_is_any_enum(t: targ_type))
593	return 0;
594
595	local_essent_len = bpf_core_essential_name_len(name: local_acc->name);
596
597	for (i = 0; i < btf_vlen(t: targ_type); i++) {
598	if (btf_is_enum(t: targ_type))
599	name_off = btf_enum(t: targ_type)[i].name_off;
600	else
601	name_off = btf_enum64(t: targ_type)[i].name_off;
602
603	targ_name = btf__name_by_offset(btf: targ_spec->btf, offset: name_off);
604	targ_essent_len = bpf_core_essential_name_len(name: 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(kind: 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(btf: targ_spec->btf, id: targ_id,
625	res_id: &targ_id);
626	if (!targ_type)
627	return -EINVAL;
628
629	if (local_acc->name) {
630	matched = bpf_core_match_member(local_btf: local_spec->btf,
631	local_acc,
632	targ_btf, targ_id,
633	spec: targ_spec, next_targ_id: &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(t: targ_type))
646	return 0;
647
648	a = btf_array(t: targ_type);
649	flex = is_flex_arr(btf: targ_btf, acc: targ_acc - 1, arr: a);
650	if (!flex && local_acc->idx >= a->nelems)
651	return 0;
652	if (!skip_mods_and_typedefs(btf: targ_btf, id: a->type,
653	res_id: &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(btf: targ_btf, type_id: 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
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(btf: spec->btf, type_id: 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(btf: spec->btf, type_id: 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(btf: spec->btf, type_id: 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(btf: spec->btf, id: m->type, res_id: &field_type_id);
732	bit_off = spec->bit_offset;
733	bit_sz = btf_member_bitfield_size(t, member_idx: 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(btf: spec->btf, type_id: 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(t: mt) && BTF_INFO_KFLAG(mt->info)) ||
779	(btf_is_int(t: mt) && (btf_int_encoding(t: 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
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(btf: spec->btf, type_id: 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
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(btf: spec->btf, type_id: 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(e: 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	*/
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(kind: relo->kind)) {
897	err = bpf_core_calc_field_relo(prog_name, relo, spec: local_spec,
898	val: &res->orig_val, field_sz: &res->orig_sz,
899	type_id: &res->orig_type_id, validate: &res->validate);
900	err = err ?: bpf_core_calc_field_relo(prog_name, relo, spec: targ_spec,
901	val: &res->new_val, field_sz: &res->new_sz,
902	type_id: &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(btf: local_spec->btf, type_id: res->orig_type_id);
914	new_t = btf_type_by_id(btf: targ_spec->btf, type_id: 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(t: orig_t) && btf_is_ptr(t: new_t))
931	goto done;
932	if (btf_is_int(t: orig_t) && btf_is_int(t: new_t) &&
933	btf_int_encoding(t: orig_t) != BTF_INT_SIGNED &&
934	btf_int_encoding(t: 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(kind: relo->kind)) {
943	err = bpf_core_calc_type_relo(relo, spec: local_spec, val: &res->orig_val, validate: &res->validate);
944	err = err ?: bpf_core_calc_type_relo(relo, spec: targ_spec, val: &res->new_val, NULL);
945	} else if (core_relo_is_enumval_based(kind: relo->kind)) {
946	err = bpf_core_calc_enumval_relo(relo, spec: local_spec, val: &res->orig_val);
947	err = err ?: bpf_core_calc_enumval_relo(relo, spec: targ_spec, val: &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	*/
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
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
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	*/
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: insn_idx + 1, insn: 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(sz: 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	*/
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(btf: spec->btf, type_id);
1176	s = btf__name_by_offset(btf: spec->btf, offset: 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(kind: spec->relo_kind))
1183	return len;
1184
1185	if (core_relo_is_enumval_based(kind: spec->relo_kind)) {
1186	t = skip_mods_and_typedefs(btf: spec->btf, id: 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(btf: spec->btf, offset: 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(btf: spec->btf, offset: 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(kind: 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	*/
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(btf: local_btf, type_id: local_id);
1300	local_name = btf__name_by_offset(btf: local_btf, offset: local_type->name_off);
1301	if (!local_name)
1302	return -EINVAL;
1303
1304	err = bpf_core_parse_spec(prog_name, btf: local_btf, relo, spec: local_spec);
1305	if (err) {
1306	const char *spec_str;
1307
1308	spec_str = btf__name_by_offset(btf: local_btf, offset: 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(buf: spec_buf, buf_sz: sizeof(spec_buf), spec: 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(s: 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, targ_btf: cands->cands[i].btf,
1339	targ_id: cands->cands[i].id, targ_spec: cand_spec);
1340	if (err < 0) {
1341	bpf_core_format_spec(buf: spec_buf, buf_sz: sizeof(spec_buf), spec: 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(buf: spec_buf, buf_sz: sizeof(spec_buf), spec: 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, targ_spec: cand_spec, res: &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, res: targ_res);
1415	if (err)
1416	return err;
1417	}
1418
1419	return 0;
1420	}
1421
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(btf: local_btf, offset: local_name_off);
1429	targ_n = btf__name_by_offset(btf: targ_btf, offset: targ_name_off);
1430
1431	if (str_is_empty(s: targ_n))
1432	return str_is_empty(s: local_n);
1433
1434	targ_len = bpf_core_essential_name_len(name: targ_n);
1435	local_len = bpf_core_essential_name_len(name: local_n);
1436
1437	return targ_len == local_len && strncmp(local_n, targ_n, local_len) == 0;
1438	}
1439
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(t: local_t);
1444	__u16 targ_vlen = btf_vlen(t: 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(t: local_t) ? btf_enum(t: local_t)[i].name_off :
1461	btf_enum64(t: local_t)[i].name_off;
1462
1463	for (j = 0; j < targ_vlen; j++) {
1464	targ_n_off = btf_is_enum(t: targ_t) ? btf_enum(t: targ_t)[j].name_off :
1465	btf_enum64(t: targ_t)[j].name_off;
1466
1467	if (bpf_core_names_match(local_btf, local_name_off: local_n_off, targ_btf, targ_name_off: targ_n_off)) {
1468	matched = true;
1469	break;
1470	}
1471	}
1472
1473	if (!matched)
1474	return 0;
1475	}
1476	return 1;
1477	}
1478
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(t: local_t);
1484	__u16 local_vlen = btf_vlen(t: local_t);
1485	__u16 targ_vlen = btf_vlen(t: 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(t: 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_name_off: local_m->name_off,
1498	targ_btf, targ_name_off: targ_m->name_off))
1499	continue;
1500
1501	err = __bpf_core_types_match(local_btf, local_id: local_m->type, targ_btf,
1502	targ_id: targ_m->type, behind_ptr, level: 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	*/
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	recur:
1555	depth--;
1556	if (depth < 0)
1557	return -EINVAL;
1558
1559	local_t = skip_mods_and_typedefs(btf: local_btf, id: local_id, res_id: &local_id);
1560	targ_t = skip_mods_and_typedefs(btf: targ_btf, id: targ_id, res_id: &targ_id);
1561	if (!local_t || !targ_t)
1562	return -EINVAL;
1563
1564	/* While the name check happens after typedefs are skipped, root-level
1565	* typedefs would still be name-matched as that's the contract with
1566	* callers.
1567	*/
1568	if (!bpf_core_names_match(local_btf, local_name_off: local_t->name_off, targ_btf, targ_name_off: targ_t->name_off))
1569	return 0;
1570
1571	local_k = btf_kind(t: local_t);
1572	targ_k = btf_kind(t: targ_t);
1573
1574	switch (local_k) {
1575	case BTF_KIND_UNKN:
1576	return local_k == targ_k;
1577	case BTF_KIND_FWD: {
1578	bool local_f = BTF_INFO_KFLAG(local_t->info);
1579
1580	if (behind_ptr) {
1581	if (local_k == targ_k)
1582	return local_f == BTF_INFO_KFLAG(targ_t->info);
1583
1584	/* for forward declarations kflag dictates whether the
1585	* target is a struct (0) or union (1)
1586	*/
1587	return (targ_k == BTF_KIND_STRUCT && !local_f) ||
1588	(targ_k == BTF_KIND_UNION && local_f);
1589	} else {
1590	if (local_k != targ_k)
1591	return 0;
1592
1593	/* match if the forward declaration is for the same kind */
1594	return local_f == BTF_INFO_KFLAG(targ_t->info);
1595	}
1596	}
1597	case BTF_KIND_ENUM:
1598	case BTF_KIND_ENUM64:
1599	if (!btf_is_any_enum(t: targ_t))
1600	return 0;
1601
1602	return bpf_core_enums_match(local_btf, local_t, targ_btf, targ_t);
1603	case BTF_KIND_STRUCT:
1604	case BTF_KIND_UNION:
1605	if (behind_ptr) {
1606	bool targ_f = BTF_INFO_KFLAG(targ_t->info);
1607
1608	if (local_k == targ_k)
1609	return 1;
1610
1611	if (targ_k != BTF_KIND_FWD)
1612	return 0;
1613
1614	return (local_k == BTF_KIND_UNION) == targ_f;
1615	} else {
1616	if (local_k != targ_k)
1617	return 0;
1618
1619	return bpf_core_composites_match(local_btf, local_t, targ_btf, targ_t,
1620	behind_ptr, level);
1621	}
1622	case BTF_KIND_INT: {
1623	__u8 local_sgn;
1624	__u8 targ_sgn;
1625
1626	if (local_k != targ_k)
1627	return 0;
1628
1629	local_sgn = btf_int_encoding(t: local_t) & BTF_INT_SIGNED;
1630	targ_sgn = btf_int_encoding(t: targ_t) & BTF_INT_SIGNED;
1631
1632	return local_t->size == targ_t->size && local_sgn == targ_sgn;
1633	}
1634	case BTF_KIND_PTR:
1635	if (local_k != targ_k)
1636	return 0;
1637
1638	behind_ptr = true;
1639
1640	local_id = local_t->type;
1641	targ_id = targ_t->type;
1642	goto recur;
1643	case BTF_KIND_ARRAY: {
1644	const struct btf_array *local_array = btf_array(t: local_t);
1645	const struct btf_array *targ_array = btf_array(t: targ_t);
1646
1647	if (local_k != targ_k)
1648	return 0;
1649
1650	if (local_array->nelems != targ_array->nelems)
1651	return 0;
1652
1653	local_id = local_array->type;
1654	targ_id = targ_array->type;
1655	goto recur;
1656	}
1657	case BTF_KIND_FUNC_PROTO: {
1658	struct btf_param *local_p = btf_params(t: local_t);
1659	struct btf_param *targ_p = btf_params(t: targ_t);
1660	__u16 local_vlen = btf_vlen(t: local_t);
1661	__u16 targ_vlen = btf_vlen(t: targ_t);
1662	int i, err;
1663
1664	if (local_k != targ_k)
1665	return 0;
1666
1667	if (local_vlen != targ_vlen)
1668	return 0;
1669
1670	for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
1671	err = __bpf_core_types_match(local_btf, local_id: local_p->type, targ_btf,
1672	targ_id: targ_p->type, behind_ptr, level: level - 1);
1673	if (err <= 0)
1674	return err;
1675	}
1676
1677	/* tail recurse for return type check */
1678	local_id = local_t->type;
1679	targ_id = targ_t->type;
1680	goto recur;
1681	}
1682	default:
1683	pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
1684	btf_kind_str(local_t), local_id, targ_id);
1685	return 0;
1686	}
1687	}
1688