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1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2
3 #ifndef _GNU_SOURCE
4 #define _GNU_SOURCE
5 #endif
6 #include <libelf.h>
7 #include <gelf.h>
8 #include <fcntl.h>
9 #include <linux/kernel.h>
10
11 #include "libbpf_internal.h"
12 #include "str_error.h"
13
14 /* A SHT_GNU_versym section holds 16-bit words. This bit is set if
15  * the symbol is hidden and can only be seen when referenced using an
16  * explicit version number. This is a GNU extension.
17  */
18 #define VERSYM_HIDDEN   0x8000
19
20 /* This is the mask for the rest of the data in a word read from a
21  * SHT_GNU_versym section.
22  */
23 #define VERSYM_VERSION  0x7fff
24
25 int elf_open(const char *binary_path, struct elf_fd *elf_fd)
26 {
27         int fd, ret;
28         Elf *elf;
29
30         elf_fd->elf = NULL;
31         elf_fd->fd = -1;
32
33         if (elf_version(EV_CURRENT) == EV_NONE) {
34                 pr_warn("elf: failed to init libelf for %s\n", binary_path);
35                 return -LIBBPF_ERRNO__LIBELF;
36         }
37         fd = open(binary_path, O_RDONLY | O_CLOEXEC);
38         if (fd < 0) {
39                 ret = -errno;
40                 pr_warn("elf: failed to open %s: %s\n", binary_path, errstr(ret));
41                 return ret;
42         }
43         elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
44         if (!elf) {
45                 pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
46                 close(fd);
47                 return -LIBBPF_ERRNO__FORMAT;
48         }
49         elf_fd->fd = fd;
50         elf_fd->elf = elf;
51         return 0;
52 }
53
54 void elf_close(struct elf_fd *elf_fd)
55 {
56         if (!elf_fd)
57                 return;
58         elf_end(elf_fd->elf);
59         close(elf_fd->fd);
60 }
61
62 /* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
63 static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
64 {
65         while ((scn = elf_nextscn(elf, scn)) != NULL) {
66                 GElf_Shdr sh;
67
68                 if (!gelf_getshdr(scn, &sh))
69                         continue;
70                 if (sh.sh_type == sh_type)
71                         return scn;
72         }
73         return NULL;
74 }
75
76 struct elf_sym {
77         const char *name;
78         GElf_Sym sym;
79         GElf_Shdr sh;
80         int ver;
81         bool hidden;
82 };
83
84 struct elf_sym_iter {
85         Elf *elf;
86         Elf_Data *syms;
87         Elf_Data *versyms;
88         Elf_Data *verdefs;
89         size_t nr_syms;
90         size_t strtabidx;
91         size_t verdef_strtabidx;
92         size_t next_sym_idx;
93         struct elf_sym sym;
94         int st_type;
95 };
96
97 static int elf_sym_iter_new(struct elf_sym_iter *iter,
98                             Elf *elf, const char *binary_path,
99                             int sh_type, int st_type)
100 {
101         Elf_Scn *scn = NULL;
102         GElf_Ehdr ehdr;
103         GElf_Shdr sh;
104
105         memset(iter, 0, sizeof(*iter));
106
107         if (!gelf_getehdr(elf, &ehdr)) {
108                 pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
109                 return -EINVAL;
110         }
111
112         scn = elf_find_next_scn_by_type(elf, sh_type, NULL);
113         if (!scn) {
114                 pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
115                          binary_path);
116                 return -ENOENT;
117         }
118
119         if (!gelf_getshdr(scn, &sh))
120                 return -EINVAL;
121
122         iter->strtabidx = sh.sh_link;
123         iter->syms = elf_getdata(scn, 0);
124         if (!iter->syms) {
125                 pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
126                         binary_path, elf_errmsg(-1));
127                 return -EINVAL;
128         }
129         iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
130         iter->elf = elf;
131         iter->st_type = st_type;
132
133         /* Version symbol table is meaningful to dynsym only */
134         if (sh_type != SHT_DYNSYM)
135                 return 0;
136
137         scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
138         if (!scn)
139                 return 0;
140         iter->versyms = elf_getdata(scn, 0);
141
142         scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
143         if (!scn)
144                 return 0;
145
146         iter->verdefs = elf_getdata(scn, 0);
147         if (!iter->verdefs || !gelf_getshdr(scn, &sh)) {
148                 pr_warn("elf: failed to get verdef ELF section in '%s'\n", binary_path);
149                 return -EINVAL;
150         }
151         iter->verdef_strtabidx = sh.sh_link;
152
153         return 0;
154 }
155
156 static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
157 {
158         struct elf_sym *ret = &iter->sym;
159         GElf_Sym *sym = &ret->sym;
160         const char *name = NULL;
161         GElf_Versym versym;
162         Elf_Scn *sym_scn;
163         size_t idx;
164
165         for (idx = iter->next_sym_idx; idx < iter->nr_syms; idx++) {
166                 if (!gelf_getsym(iter->syms, idx, sym))
167                         continue;
168                 if (GELF_ST_TYPE(sym->st_info) != iter->st_type)
169                         continue;
170                 name = elf_strptr(iter->elf, iter->strtabidx, sym->st_name);
171                 if (!name)
172                         continue;
173                 sym_scn = elf_getscn(iter->elf, sym->st_shndx);
174                 if (!sym_scn)
175                         continue;
176                 if (!gelf_getshdr(sym_scn, &ret->sh))
177                         continue;
178
179                 iter->next_sym_idx = idx + 1;
180                 ret->name = name;
181                 ret->ver = 0;
182                 ret->hidden = false;
183
184                 if (iter->versyms) {
185                         if (!gelf_getversym(iter->versyms, idx, &versym))
186                                 continue;
187                         ret->ver = versym & VERSYM_VERSION;
188                         ret->hidden = versym & VERSYM_HIDDEN;
189                 }
190                 return ret;
191         }
192
193         return NULL;
194 }
195
196 static const char *elf_get_vername(struct elf_sym_iter *iter, int ver)
197 {
198         GElf_Verdaux verdaux;
199         GElf_Verdef verdef;
200         int offset;
201
202         if (!iter->verdefs)
203                 return NULL;
204
205         offset = 0;
206         while (gelf_getverdef(iter->verdefs, offset, &verdef)) {
207                 if (verdef.vd_ndx != ver) {
208                         if (!verdef.vd_next)
209                                 break;
210
211                         offset += verdef.vd_next;
212                         continue;
213                 }
214
215                 if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux))
216                         break;
217
218                 return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name);
219
220         }
221         return NULL;
222 }
223
224 static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym,
225                          const char *name, size_t name_len, const char *lib_ver)
226 {
227         const char *ver_name;
228
229         /* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER
230          * make sure the func part matches the user specified name
231          */
232         if (strncmp(sym->name, name, name_len) != 0)
233                 return false;
234
235         /* ...but we don't want a search for "foo" to match 'foo2" also, so any
236          * additional characters in sname should be of the form "@@LIB".
237          */
238         if (sym->name[name_len] != '\0' && sym->name[name_len] != '@')
239                 return false;
240
241         /* If user does not specify symbol version, then we got a match */
242         if (!lib_ver)
243                 return true;
244
245         /* If user specifies symbol version, for dynamic symbols,
246          * get version name from ELF verdef section for comparison.
247          */
248         if (sh_type == SHT_DYNSYM) {
249                 ver_name = elf_get_vername(iter, sym->ver);
250                 if (!ver_name)
251                         return false;
252                 return strcmp(ver_name, lib_ver) == 0;
253         }
254
255         /* For normal symbols, it is already in form of func@LIB_VER */
256         return strcmp(sym->name, name) == 0;
257 }
258
259 /* Transform symbol's virtual address (absolute for binaries and relative
260  * for shared libs) into file offset, which is what kernel is expecting
261  * for uprobe/uretprobe attachment.
262  * See Documentation/trace/uprobetracer.rst for more details. This is done
263  * by looking up symbol's containing section's header and using iter's virtual
264  * address (sh_addr) and corresponding file offset (sh_offset) to transform
265  * sym.st_value (virtual address) into desired final file offset.
266  */
267 static unsigned long elf_sym_offset(struct elf_sym *sym)
268 {
269         return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
270 }
271
272 /* Find offset of function name in the provided ELF object. "binary_path" is
273  * the path to the ELF binary represented by "elf", and only used for error
274  * reporting matters. "name" matches symbol name or name@@LIB for library
275  * functions.
276  */
277 long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
278 {
279         int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
280         const char *at_symbol, *lib_ver;
281         bool is_shared_lib;
282         long ret = -ENOENT;
283         size_t name_len;
284         GElf_Ehdr ehdr;
285
286         if (!gelf_getehdr(elf, &ehdr)) {
287                 pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
288                 ret = -LIBBPF_ERRNO__FORMAT;
289                 goto out;
290         }
291         /* for shared lib case, we do not need to calculate relative offset */
292         is_shared_lib = ehdr.e_type == ET_DYN;
293
294         /* Does name specify "@@LIB_VER" or "@LIB_VER" ? */
295         at_symbol = strchr(name, '@');
296         if (at_symbol) {
297                 name_len = at_symbol - name;
298                 /* skip second @ if it's @@LIB_VER case */
299                 if (at_symbol[1] == '@')
300                         at_symbol++;
301                 lib_ver = at_symbol + 1;
302         } else {
303                 name_len = strlen(name);
304                 lib_ver = NULL;
305         }
306
307         /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
308          * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
309          * linked binary may not have SHT_DYMSYM, so absence of a section should not be
310          * reported as a warning/error.
311          */
312         for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
313                 struct elf_sym_iter iter;
314                 struct elf_sym *sym;
315                 int last_bind = -1;
316                 int cur_bind;
317
318                 ret = elf_sym_iter_new(&iter, elf, binary_path, sh_types[i], STT_FUNC);
319                 if (ret == -ENOENT)
320                         continue;
321                 if (ret)
322                         goto out;
323
324                 while ((sym = elf_sym_iter_next(&iter))) {
325                         if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver))
326                                 continue;
327
328                         cur_bind = GELF_ST_BIND(sym->sym.st_info);
329
330                         if (ret > 0) {
331                                 /* handle multiple matches */
332                                 if (elf_sym_offset(sym) == ret) {
333                                         /* same offset, no problem */
334                                         continue;
335                                 } else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
336                                         /* Only accept one non-weak bind. */
337                                         pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
338                                                 sym->name, name, binary_path);
339                                         ret = -LIBBPF_ERRNO__FORMAT;
340                                         goto out;
341                                 } else if (cur_bind == STB_WEAK) {
342                                         /* already have a non-weak bind, and
343                                          * this is a weak bind, so ignore.
344                                          */
345                                         continue;
346                                 }
347                         }
348
349                         ret = elf_sym_offset(sym);
350                         last_bind = cur_bind;
351                 }
352                 if (ret > 0)
353                         break;
354         }
355
356         if (ret > 0) {
357                 pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
358                          ret);
359         } else {
360                 if (ret == 0) {
361                         pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
362                                 is_shared_lib ? "should not be 0 in a shared library" :
363                                                 "try using shared library path instead");
364                         ret = -ENOENT;
365                 } else {
366                         pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
367                 }
368         }
369 out:
370         return ret;
371 }
372
373 /* Find offset of function name in ELF object specified by path. "name" matches
374  * symbol name or name@@LIB for library functions.
375  */
376 long elf_find_func_offset_from_file(const char *binary_path, const char *name)
377 {
378         struct elf_fd elf_fd;
379         long ret = -ENOENT;
380
381         ret = elf_open(binary_path, &elf_fd);
382         if (ret)
383                 return ret;
384         ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
385         elf_close(&elf_fd);
386         return ret;
387 }
388
389 struct symbol {
390         const char *name;
391         int bind;
392         int idx;
393 };
394
395 static int symbol_cmp(const void *a, const void *b)
396 {
397         const struct symbol *sym_a = a;
398         const struct symbol *sym_b = b;
399
400         return strcmp(sym_a->name, sym_b->name);
401 }
402
403 /*
404  * Return offsets in @poffsets for symbols specified in @syms array argument.
405  * On success returns 0 and offsets are returned in allocated array with @cnt
406  * size, that needs to be released by the caller.
407  */
408 int elf_resolve_syms_offsets(const char *binary_path, int cnt,
409                              const char **syms, unsigned long **poffsets,
410                              int st_type)
411 {
412         int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
413         int err = 0, i, cnt_done = 0;
414         unsigned long *offsets;
415         struct symbol *symbols;
416         struct elf_fd elf_fd;
417
418         err = elf_open(binary_path, &elf_fd);
419         if (err)
420                 return err;
421
422         offsets = calloc(cnt, sizeof(*offsets));
423         symbols = calloc(cnt, sizeof(*symbols));
424
425         if (!offsets || !symbols) {
426                 err = -ENOMEM;
427                 goto out;
428         }
429
430         for (i = 0; i < cnt; i++) {
431                 symbols[i].name = syms[i];
432                 symbols[i].idx = i;
433         }
434
435         qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);
436
437         for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
438                 struct elf_sym_iter iter;
439                 struct elf_sym *sym;
440
441                 err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], st_type);
442                 if (err == -ENOENT)
443                         continue;
444                 if (err)
445                         goto out;
446
447                 while ((sym = elf_sym_iter_next(&iter))) {
448                         unsigned long sym_offset = elf_sym_offset(sym);
449                         int bind = GELF_ST_BIND(sym->sym.st_info);
450                         struct symbol *found, tmp = {
451                                 .name = sym->name,
452                         };
453                         unsigned long *offset;
454
455                         found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
456                         if (!found)
457                                 continue;
458
459                         offset = &offsets[found->idx];
460                         if (*offset > 0) {
461                                 /* same offset, no problem */
462                                 if (*offset == sym_offset)
463                                         continue;
464                                 /* handle multiple matches */
465                                 if (found->bind != STB_WEAK && bind != STB_WEAK) {
466                                         /* Only accept one non-weak bind. */
467                                         pr_warn("elf: ambiguous match found '%s@%lu' in '%s' previous offset %lu\n",
468                                                 sym->name, sym_offset, binary_path, *offset);
469                                         err = -ESRCH;
470                                         goto out;
471                                 } else if (bind == STB_WEAK) {
472                                         /* already have a non-weak bind, and
473                                          * this is a weak bind, so ignore.
474                                          */
475                                         continue;
476                                 }
477                         } else {
478                                 cnt_done++;
479                         }
480                         *offset = sym_offset;
481                         found->bind = bind;
482                 }
483         }
484
485         if (cnt != cnt_done) {
486                 err = -ENOENT;
487                 goto out;
488         }
489
490         *poffsets = offsets;
491
492 out:
493         free(symbols);
494         if (err)
495                 free(offsets);
496         elf_close(&elf_fd);
497         return err;
498 }
499
500 /*
501  * Return offsets in @poffsets for symbols specified by @pattern argument.
502  * On success returns 0 and offsets are returned in allocated @poffsets
503  * array with the @pctn size, that needs to be released by the caller.
504  */
505 int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
506                                 unsigned long **poffsets, size_t *pcnt)
507 {
508         int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM };
509         unsigned long *offsets = NULL;
510         size_t cap = 0, cnt = 0;
511         struct elf_fd elf_fd;
512         int err = 0, i;
513
514         err = elf_open(binary_path, &elf_fd);
515         if (err)
516                 return err;
517
518         for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
519                 struct elf_sym_iter iter;
520                 struct elf_sym *sym;
521
522                 err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
523                 if (err == -ENOENT)
524                         continue;
525                 if (err)
526                         goto out;
527
528                 while ((sym = elf_sym_iter_next(&iter))) {
529                         if (!glob_match(sym->name, pattern))
530                                 continue;
531
532                         err = libbpf_ensure_mem((void **) &offsets, &cap, sizeof(*offsets),
533                                                 cnt + 1);
534                         if (err)
535                                 goto out;
536
537                         offsets[cnt++] = elf_sym_offset(sym);
538                 }
539
540                 /* If we found anything in the first symbol section,
541                  * do not search others to avoid duplicates.
542                  */
543                 if (cnt)
544                         break;
545         }
546
547         if (cnt) {
548                 *poffsets = offsets;
549                 *pcnt = cnt;
550         } else {
551                 err = -ENOENT;
552         }
553
554 out:
555         if (err)
556                 free(offsets);
557         elf_close(&elf_fd);
558         return err;
559 }
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