src/liblttng-ust/lttng-ust-elf.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-or-later
   3  *
   4  * Copyright (C) 2015 Antoine Busque <abusque@efficios.com>
   5  */
   6
   7 #define _LGPL_SOURCE
   8 #include <fcntl.h>
   9 #include <stdbool.h>
  10 #include <stdint.h>
  11 #include <string.h>
  12 #include <sys/stat.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15
  16 #include <lttng/ust-utils.h>
  17
  18 #include <ust-elf.h>
  19 #include <ust-fd.h>
  20
  21 #include "lttng-tracer-core.h"
  22 #include "lttng-ust-elf.h"
  23 #include "ust-helper.h"
  24
  25 #define BUF_LEN 4096
  26
  27 #ifndef NT_GNU_BUILD_ID
  28 # define NT_GNU_BUILD_ID        3
  29 #endif
  30
  31 /*
  32  * Retrieve the nth (where n is the `index` argument) phdr (program
  33  * header) from the given elf instance.
  34  *
  35  * A pointer to the phdr is returned on success, NULL on failure.
  36  */
  37 static
  38 struct lttng_ust_elf_phdr *lttng_ust_elf_get_phdr(struct lttng_ust_elf *elf,
  39                                                 uint16_t index)
  40 {
  41         struct lttng_ust_elf_phdr *phdr = NULL;
  42         off_t offset;
  43
  44         if (!elf) {
  45                 goto error;
  46         }
  47
  48         if (index >= elf->ehdr->e_phnum) {
  49                 goto error;
  50         }
  51
  52         phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
  53         if (!phdr) {
  54                 goto error;
  55         }
  56
  57         offset = (off_t) elf->ehdr->e_phoff
  58                         + (off_t) index * elf->ehdr->e_phentsize;
  59         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
  60                 goto error;
  61         }
  62
  63         if (is_elf_32_bit(elf)) {
  64                 Elf32_Phdr elf_phdr;
  65
  66                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  67                                 < sizeof(elf_phdr)) {
  68                         goto error;
  69                 }
  70                 if (!is_elf_native_endian(elf)) {
  71                         bswap_phdr(elf_phdr);
  72                 }
  73                 copy_phdr(elf_phdr, *phdr);
  74         } else {
  75                 Elf64_Phdr elf_phdr;
  76
  77                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  78                                 < sizeof(elf_phdr)) {
  79                         goto error;
  80                 }
  81                 if (!is_elf_native_endian(elf)) {
  82                         bswap_phdr(elf_phdr);
  83                 }
  84                 copy_phdr(elf_phdr, *phdr);
  85         }
  86
  87         return phdr;
  88
  89 error:
  90         free(phdr);
  91         return NULL;
  92 }
  93
  94 /*
  95  * Retrieve the nth (where n is the `index` argument) shdr (section
  96  * header) from the given elf instance.
  97  *
  98  * A pointer to the shdr is returned on success, NULL on failure.
  99  */
 100 static
 101 struct lttng_ust_elf_shdr *lttng_ust_elf_get_shdr(struct lttng_ust_elf *elf,
 102                                                 uint16_t index)
 103 {
 104         struct lttng_ust_elf_shdr *shdr = NULL;
 105         off_t offset;
 106
 107         if (!elf) {
 108                 goto error;
 109         }
 110
 111         if (index >= elf->ehdr->e_shnum) {
 112                 goto error;
 113         }
 114
 115         shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
 116         if (!shdr) {
 117                 goto error;
 118         }
 119
 120         offset = (off_t) elf->ehdr->e_shoff
 121                         + (off_t) index * elf->ehdr->e_shentsize;
 122         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 123                 goto error;
 124         }
 125
 126         if (is_elf_32_bit(elf)) {
 127                 Elf32_Shdr elf_shdr;
 128
 129                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 130                                 < sizeof(elf_shdr)) {
 131                         goto error;
 132                 }
 133                 if (!is_elf_native_endian(elf)) {
 134                         bswap_shdr(elf_shdr);
 135                 }
 136                 copy_shdr(elf_shdr, *shdr);
 137         } else {
 138                 Elf64_Shdr elf_shdr;
 139
 140                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 141                                 < sizeof(elf_shdr)) {
 142                         goto error;
 143                 }
 144                 if (!is_elf_native_endian(elf)) {
 145                         bswap_shdr(elf_shdr);
 146                 }
 147                 copy_shdr(elf_shdr, *shdr);
 148         }
 149
 150         return shdr;
 151
 152 error:
 153         free(shdr);
 154         return NULL;
 155 }
 156
 157 /*
 158  * Lookup a section's name from a given offset (usually from an shdr's
 159  * sh_name value) in bytes relative to the beginning of the section
 160  * names string table.
 161  *
 162  * If no name is found, NULL is returned.
 163  */
 164 static
 165 char *lttng_ust_elf_get_section_name(struct lttng_ust_elf *elf, off_t offset)
 166 {
 167         char *name = NULL;
 168         size_t len = 0, to_read;        /* len does not include \0 */
 169
 170         if (!elf) {
 171                 goto error;
 172         }
 173
 174         if (offset >= elf->section_names_size) {
 175                 goto error;
 176         }
 177
 178         if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
 179                 goto error;
 180         }
 181
 182         to_read = elf->section_names_size - offset;
 183
 184         /* Find first \0 after or at current location, remember len. */
 185         for (;;) {
 186                 char buf[BUF_LEN];
 187                 ssize_t read_len;
 188                 size_t i;
 189
 190                 if (!to_read) {
 191                         goto error;
 192                 }
 193                 read_len = lttng_ust_read(elf->fd, buf,
 194                         min_t(size_t, BUF_LEN, to_read));
 195                 if (read_len <= 0) {
 196                         goto error;
 197                 }
 198                 for (i = 0; i < read_len; i++) {
 199                         if (buf[i] == '\0') {
 200                                 len += i;
 201                                 goto end;
 202                         }
 203                 }
 204                 len += read_len;
 205                 to_read -= read_len;
 206         }
 207 end:
 208         name = zmalloc(sizeof(char) * (len + 1));       /* + 1 for \0 */
 209         if (!name) {
 210                 goto error;
 211         }
 212         if (lseek(elf->fd, elf->section_names_offset + offset,
 213                 SEEK_SET) < 0) {
 214                 goto error;
 215         }
 216         if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
 217                 goto error;
 218         }
 219
 220         return name;
 221
 222 error:
 223         free(name);
 224         return NULL;
 225 }
 226
 227 /*
 228  * Create an instance of lttng_ust_elf for the ELF file located at
 229  * `path`.
 230  *
 231  * Return a pointer to the instance on success, NULL on failure.
 232  */
 233 struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 234 {
 235         uint8_t e_ident[EI_NIDENT];
 236         struct lttng_ust_elf_shdr *section_names_shdr;
 237         struct lttng_ust_elf *elf = NULL;
 238         int ret, fd;
 239
 240         elf = zmalloc(sizeof(struct lttng_ust_elf));
 241         if (!elf) {
 242                 goto error;
 243         }
 244
 245         /* Initialize fd field to -1. 0 is a valid fd number */
 246         elf->fd = -1;
 247
 248         elf->path = strdup(path);
 249         if (!elf->path) {
 250                 goto error;
 251         }
 252
 253         lttng_ust_lock_fd_tracker();
 254         fd = open(elf->path, O_RDONLY | O_CLOEXEC);
 255         if (fd < 0) {
 256                 lttng_ust_unlock_fd_tracker();
 257                 goto error;
 258         }
 259
 260         ret = lttng_ust_add_fd_to_tracker(fd);
 261         if (ret < 0) {
 262                 ret = close(fd);
 263                 if (ret) {
 264                         PERROR("close on elf->fd");
 265                 }
 266                 ret = -1;
 267                 lttng_ust_unlock_fd_tracker();
 268                 goto error;
 269         }
 270         elf->fd = ret;
 271         lttng_ust_unlock_fd_tracker();
 272
 273         if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 274                 goto error;
 275         }
 276         elf->bitness = e_ident[EI_CLASS];
 277         elf->endianness = e_ident[EI_DATA];
 278
 279         if (lseek(elf->fd, 0, SEEK_SET) < 0) {
 280                 goto error;
 281         }
 282
 283         elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
 284         if (!elf->ehdr) {
 285                 goto error;
 286         }
 287
 288         if (is_elf_32_bit(elf)) {
 289                 Elf32_Ehdr elf_ehdr;
 290
 291                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 292                                 < sizeof(elf_ehdr)) {
 293                         goto error;
 294                 }
 295                 if (!is_elf_native_endian(elf)) {
 296                         bswap_ehdr(elf_ehdr);
 297                 }
 298                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 299         } else {
 300                 Elf64_Ehdr elf_ehdr;
 301
 302                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 303                                 < sizeof(elf_ehdr)) {
 304                         goto error;
 305                 }
 306                 if (!is_elf_native_endian(elf)) {
 307                         bswap_ehdr(elf_ehdr);
 308                 }
 309                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 310         }
 311
 312         section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
 313         if (!section_names_shdr) {
 314                 goto error;
 315         }
 316
 317         elf->section_names_offset = section_names_shdr->sh_offset;
 318         elf->section_names_size = section_names_shdr->sh_size;
 319
 320         free(section_names_shdr);
 321         return elf;
 322
 323 error:
 324         lttng_ust_elf_destroy(elf);
 325         return NULL;
 326 }
 327
 328 /*
 329  * Test whether the ELF file is position independent code (PIC)
 330  */
 331 uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
 332 {
 333         /*
 334          * PIC has and e_type value of ET_DYN, see ELF specification
 335          * version 1.1 p. 1-3.
 336          */
 337         return elf->ehdr->e_type == ET_DYN;
 338 }
 339
 340 /*
 341  * Destroy the given lttng_ust_elf instance.
 342  */
 343 void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
 344 {
 345         int ret;
 346
 347         if (!elf) {
 348                 return;
 349         }
 350
 351         if (elf->fd >= 0) {
 352                 lttng_ust_lock_fd_tracker();
 353                 ret = close(elf->fd);
 354                 if (!ret) {
 355                         lttng_ust_delete_fd_from_tracker(elf->fd);
 356                 } else {
 357                         PERROR("close");
 358                         abort();
 359                 }
 360                 lttng_ust_unlock_fd_tracker();
 361         }
 362
 363         free(elf->ehdr);
 364         free(elf->path);
 365         free(elf);
 366 }
 367
 368 /*
 369  * Compute the total in-memory size of the ELF file, in bytes.
 370  *
 371  * Returns 0 if successful, -1 if not. On success, the memory size is
 372  * returned through the out parameter `memsz`.
 373  */
 374 int lttng_ust_elf_get_memsz(struct lttng_ust_elf *elf, uint64_t *memsz)
 375 {
 376         uint16_t i;
 377         uint64_t low_addr = UINT64_MAX, high_addr = 0;
 378
 379         if (!elf || !memsz) {
 380                 goto error;
 381         }
 382
 383         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 384                 struct lttng_ust_elf_phdr *phdr;
 385
 386                 phdr = lttng_ust_elf_get_phdr(elf, i);
 387                 if (!phdr) {
 388                         goto error;
 389                 }
 390
 391                 /*
 392                  * Only PT_LOAD segments contribute to memsz. Skip
 393                  * other segments.
 394                  */
 395                 if (phdr->p_type != PT_LOAD) {
 396                         goto next_loop;
 397                 }
 398
 399                 low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
 400                 high_addr = max_t(uint64_t, high_addr,
 401                                 phdr->p_vaddr + phdr->p_memsz);
 402         next_loop:
 403                 free(phdr);
 404         }
 405
 406         if (high_addr < low_addr) {
 407                 /* No PT_LOAD segments or corrupted data. */
 408                 goto error;
 409         }
 410
 411         *memsz = high_addr - low_addr;
 412         return 0;
 413 error:
 414         return -1;
 415 }
 416
 417 /*
 418  * Internal method used to try and get the build_id from a PT_NOTE
 419  * segment ranging from `offset` to `segment_end`.
 420  *
 421  * If the function returns successfully, the out parameter `found`
 422  * indicates whether the build id information was present in the
 423  * segment or not. If `found` is not 0, the out parameters `build_id`
 424  * and `length` will both have been set with the retrieved
 425  * information.
 426  *
 427  * Returns 0 on success, -1 if an error occurred.
 428  */
 429 static
 430 int lttng_ust_elf_get_build_id_from_segment(
 431         struct lttng_ust_elf *elf, uint8_t **build_id, size_t *length,
 432         off_t offset, off_t segment_end)
 433 {
 434         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 435         size_t _length = 0;             /* Silence old gcc warning. */
 436
 437         while (offset < segment_end) {
 438                 struct lttng_ust_elf_nhdr nhdr;
 439                 size_t read_len;
 440
 441                 /* Align start of note entry */
 442                 offset += lttng_ust_offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
 443                 if (offset >= segment_end) {
 444                         break;
 445                 }
 446                 /*
 447                  * We seek manually because if the note isn't the
 448                  * build id the data following the header will not
 449                  * have been read.
 450                  */
 451                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 452                         goto error;
 453                 }
 454                 if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
 455                                 < sizeof(nhdr)) {
 456                         goto error;
 457                 }
 458
 459                 if (!is_elf_native_endian(elf)) {
 460                         nhdr.n_namesz = bswap_32(nhdr.n_namesz);
 461                         nhdr.n_descsz = bswap_32(nhdr.n_descsz);
 462                         nhdr.n_type = bswap_32(nhdr.n_type);
 463                 }
 464
 465                 offset += sizeof(nhdr) + nhdr.n_namesz;
 466                 /* Align start of desc entry */
 467                 offset += lttng_ust_offset_align(offset, ELF_NOTE_DESC_ALIGN);
 468
 469                 if (nhdr.n_type != NT_GNU_BUILD_ID) {
 470                         /*
 471                          * Ignore non build id notes but still
 472                          * increase the offset.
 473                          */
 474                         offset += nhdr.n_descsz;
 475                         continue;
 476                 }
 477
 478                 _length = nhdr.n_descsz;
 479                 _build_id = zmalloc(sizeof(uint8_t) * _length);
 480                 if (!_build_id) {
 481                         goto error;
 482                 }
 483
 484                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 485                         goto error;
 486                 }
 487                 read_len = sizeof(*_build_id) * _length;
 488                 if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
 489                         goto error;
 490                 }
 491
 492                 break;
 493         }
 494
 495         if (_build_id) {
 496                 *build_id = _build_id;
 497                 *length = _length;
 498         }
 499
 500         return 0;
 501 error:
 502         free(_build_id);
 503         return -1;
 504 }
 505
 506 /*
 507  * Retrieve a build ID (an array of bytes) from the corresponding
 508  * section in the ELF file. The length of the build ID can be either
 509  * 16 or 20 bytes depending on the method used to generate it, hence
 510  * the length out parameter.
 511  *
 512  * If the function returns successfully, the out parameter `found`
 513  * indicates whether the build id information was present in the ELF
 514  * file or not. If `found` is not 0, the out parameters `build_id` and
 515  * `length` will both have been set with the retrieved information.
 516  *
 517  * Returns 0 on success, -1 if an error occurred.
 518  */
 519 int lttng_ust_elf_get_build_id(struct lttng_ust_elf *elf, uint8_t **build_id,
 520                         size_t *length, int *found)
 521 {
 522         uint16_t i;
 523         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 524         size_t _length = 0;             /* Silence old gcc warning. */
 525
 526         if (!elf || !build_id || !length || !found) {
 527                 goto error;
 528         }
 529
 530         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 531                 off_t offset, segment_end;
 532                 struct lttng_ust_elf_phdr *phdr;
 533                 int ret = 0;
 534
 535                 phdr = lttng_ust_elf_get_phdr(elf, i);
 536                 if (!phdr) {
 537                         goto error;
 538                 }
 539
 540                 /* Build ID will be contained in a PT_NOTE segment. */
 541                 if (phdr->p_type != PT_NOTE) {
 542                         goto next_loop;
 543                 }
 544
 545                 offset = phdr->p_offset;
 546                 segment_end = offset + phdr->p_filesz;
 547                 ret = lttng_ust_elf_get_build_id_from_segment(
 548                         elf, &_build_id, &_length, offset, segment_end);
 549         next_loop:
 550                 free(phdr);
 551                 if (ret) {
 552                         goto error;
 553                 }
 554                 if (_build_id) {
 555                         break;
 556                 }
 557         }
 558
 559         if (_build_id) {
 560                 *build_id = _build_id;
 561                 *length = _length;
 562                 *found = 1;
 563         } else {
 564                 *found = 0;
 565         }
 566
 567         return 0;
 568 error:
 569         free(_build_id);
 570         return -1;
 571 }
 572
 573 /*
 574  * Try to retrieve filename and CRC from given ELF section `shdr`.
 575  *
 576  * If the function returns successfully, the out parameter `found`
 577  * indicates whether the debug link information was present in the ELF
 578  * section or not. If `found` is not 0, the out parameters `filename` and
 579  * `crc` will both have been set with the retrieved information.
 580  *
 581  * Returns 0 on success, -1 if an error occurred.
 582  */
 583 static
 584 int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
 585                                         char **filename, uint32_t *crc,
 586                                         struct lttng_ust_elf_shdr *shdr)
 587 {
 588         char *_filename = NULL;         /* Silence old gcc warning. */
 589         size_t filename_len;
 590         char *section_name = NULL;
 591         uint32_t _crc = 0;              /* Silence old gcc warning. */
 592
 593         if (!elf || !filename || !crc || !shdr) {
 594                 goto error;
 595         }
 596
 597         /*
 598          * The .gnu_debuglink section is of type SHT_PROGBITS,
 599          * skip the other sections.
 600          */
 601         if (shdr->sh_type != SHT_PROGBITS) {
 602                 goto end;
 603         }
 604
 605         section_name = lttng_ust_elf_get_section_name(elf,
 606                                                 shdr->sh_name);
 607         if (!section_name) {
 608                 goto end;
 609         }
 610         if (strcmp(section_name, ".gnu_debuglink")) {
 611                 goto end;
 612         }
 613
 614         /*
 615          * The length of the filename is the sh_size excluding the CRC
 616          * which comes after it in the section.
 617          */
 618         _filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
 619         if (!_filename) {
 620                 goto error;
 621         }
 622         if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
 623                 goto error;
 624         }
 625         filename_len = sizeof(*_filename) * (shdr->sh_size - ELF_CRC_SIZE);
 626         if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
 627                 goto error;
 628         }
 629         if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
 630                 goto error;
 631         }
 632         if (!is_elf_native_endian(elf)) {
 633                 _crc = bswap_32(_crc);
 634         }
 635
 636 end:
 637         free(section_name);
 638         if (_filename) {
 639                 *filename = _filename;
 640                 *crc = _crc;
 641         }
 642
 643         return 0;
 644
 645 error:
 646         free(_filename);
 647         free(section_name);
 648         return -1;
 649 }
 650
 651 /*
 652  * Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
 653  *
 654  * If the function returns successfully, the out parameter `found`
 655  * indicates whether the debug link information was present in the ELF
 656  * file or not. If `found` is not 0, the out parameters `filename` and
 657  * `crc` will both have been set with the retrieved information.
 658  *
 659  * Returns 0 on success, -1 if an error occurred.
 660  */
 661 int lttng_ust_elf_get_debug_link(struct lttng_ust_elf *elf, char **filename,
 662                                 uint32_t *crc, int *found)
 663 {
 664         int ret;
 665         uint16_t i;
 666         char *_filename = NULL;         /* Silence old gcc warning. */
 667         uint32_t _crc = 0;              /* Silence old gcc warning. */
 668
 669         if (!elf || !filename || !crc || !found) {
 670                 goto error;
 671         }
 672
 673         for (i = 0; i < elf->ehdr->e_shnum; ++i) {
 674                 struct lttng_ust_elf_shdr *shdr = NULL;
 675
 676                 shdr = lttng_ust_elf_get_shdr(elf, i);
 677                 if (!shdr) {
 678                         goto error;
 679                 }
 680
 681                 ret = lttng_ust_elf_get_debug_link_from_section(
 682                         elf, &_filename, &_crc, shdr);
 683                 free(shdr);
 684
 685                 if (ret) {
 686                         goto error;
 687                 }
 688                 if (_filename) {
 689                         break;
 690                 }
 691         }
 692
 693         if (_filename) {
 694                 *filename = _filename;
 695                 *crc = _crc;
 696                 *found = 1;
 697         } else {
 698                 *found = 0;
 699         }
 700
 701         return 0;
 702
 703 error:
 704         free(_filename);
 705         return -1;
 706 }