1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * genelf.c 4 * Copyright (C) 2014, Google, Inc 5 * 6 * Contributed by: 7 * Stephane Eranian <eranian@gmail.com> 8 */ 9 10 #include <sys/types.h> 11 #include <stddef.h> 12 #include <libelf.h> 13 #include <string.h> 14 #include <stdlib.h> 15 #include <unistd.h> 16 #include <inttypes.h> 17 #include <fcntl.h> 18 #include <err.h> 19 #ifdef HAVE_DWARF_SUPPORT 20 #include <dwarf.h> 21 #endif 22 23 #include "genelf.h" 24 #include "../util/jitdump.h" 25 #include <linux/compiler.h> 26 27 #ifndef NT_GNU_BUILD_ID 28 #define NT_GNU_BUILD_ID 3 29 #endif 30 31 #define BUILD_ID_URANDOM /* different uuid for each run */ 32 33 #ifdef HAVE_LIBCRYPTO_SUPPORT 34 35 #define BUILD_ID_MD5 36 #undef BUILD_ID_SHA /* does not seem to work well when linked with Java */ 37 #undef BUILD_ID_URANDOM /* different uuid for each run */ 38 39 #ifdef BUILD_ID_SHA 40 #include <openssl/sha.h> 41 #endif 42 43 #ifdef BUILD_ID_MD5 44 #include <openssl/evp.h> 45 #include <openssl/md5.h> 46 #endif 47 #endif 48 49 50 typedef struct { 51 unsigned int namesz; /* Size of entry's owner string */ 52 unsigned int descsz; /* Size of the note descriptor */ 53 unsigned int type; /* Interpretation of the descriptor */ 54 char name[0]; /* Start of the name+desc data */ 55 } Elf_Note; 56 57 struct options { 58 char *output; 59 int fd; 60 }; 61 62 static char shd_string_table[] = { 63 0, 64 '.', 't', 'e', 'x', 't', 0, /* 1 */ 65 '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */ 66 '.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */ 67 '.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */ 68 '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */ 69 '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */ 70 '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */ 71 '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */ 72 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */ 73 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */ 74 }; 75 76 static struct buildid_note { 77 Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */ 78 char name[4]; /* GNU\0 */ 79 char build_id[20]; 80 } bnote; 81 82 static Elf_Sym symtab[]={ 83 /* symbol 0 MUST be the undefined symbol */ 84 { .st_name = 0, /* index in sym_string table */ 85 .st_info = ELF_ST_TYPE(STT_NOTYPE), 86 .st_shndx = 0, /* for now */ 87 .st_value = 0x0, 88 .st_other = ELF_ST_VIS(STV_DEFAULT), 89 .st_size = 0, 90 }, 91 { .st_name = 1, /* index in sym_string table */ 92 .st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC), 93 .st_shndx = 1, 94 .st_value = 0, /* for now */ 95 .st_other = ELF_ST_VIS(STV_DEFAULT), 96 .st_size = 0, /* for now */ 97 } 98 }; 99 100 #ifdef BUILD_ID_URANDOM 101 static void 102 gen_build_id(struct buildid_note *note, 103 unsigned long load_addr __maybe_unused, 104 const void *code __maybe_unused, 105 size_t csize __maybe_unused) 106 { 107 int fd; 108 size_t sz = sizeof(note->build_id); 109 ssize_t sret; 110 111 fd = open("/dev/urandom", O_RDONLY); 112 if (fd == -1) 113 err(1, "cannot access /dev/urandom for buildid"); 114 115 sret = read(fd, note->build_id, sz); 116 117 close(fd); 118 119 if (sret != (ssize_t)sz) 120 memset(note->build_id, 0, sz); 121 } 122 #endif 123 124 #ifdef BUILD_ID_SHA 125 static void 126 gen_build_id(struct buildid_note *note, 127 unsigned long load_addr __maybe_unused, 128 const void *code, 129 size_t csize) 130 { 131 if (sizeof(note->build_id) < SHA_DIGEST_LENGTH) 132 errx(1, "build_id too small for SHA1"); 133 134 SHA1(code, csize, (unsigned char *)note->build_id); 135 } 136 #endif 137 138 #ifdef BUILD_ID_MD5 139 static void 140 gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize) 141 { 142 EVP_MD_CTX *mdctx; 143 144 if (sizeof(note->build_id) < 16) 145 errx(1, "build_id too small for MD5"); 146 147 mdctx = EVP_MD_CTX_new(); 148 if (!mdctx) 149 errx(2, "failed to create EVP_MD_CTX"); 150 151 EVP_DigestInit_ex(mdctx, EVP_md5(), NULL); 152 EVP_DigestUpdate(mdctx, &load_addr, sizeof(load_addr)); 153 EVP_DigestUpdate(mdctx, code, csize); 154 EVP_DigestFinal_ex(mdctx, (unsigned char *)note->build_id, NULL); 155 EVP_MD_CTX_free(mdctx); 156 } 157 #endif 158 159 static int 160 jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size, 161 uint64_t unwinding_size, uint64_t base_offset) 162 { 163 Elf_Data *d; 164 Elf_Scn *scn; 165 Elf_Shdr *shdr; 166 uint64_t unwinding_table_size = unwinding_size - unwinding_header_size; 167 168 /* 169 * setup eh_frame section 170 */ 171 scn = elf_newscn(e); 172 if (!scn) { 173 warnx("cannot create section"); 174 return -1; 175 } 176 177 d = elf_newdata(scn); 178 if (!d) { 179 warnx("cannot get new data"); 180 return -1; 181 } 182 183 d->d_align = 8; 184 d->d_off = 0LL; 185 d->d_buf = unwinding; 186 d->d_type = ELF_T_BYTE; 187 d->d_size = unwinding_table_size; 188 d->d_version = EV_CURRENT; 189 190 shdr = elf_getshdr(scn); 191 if (!shdr) { 192 warnx("cannot get section header"); 193 return -1; 194 } 195 196 shdr->sh_name = 104; 197 shdr->sh_type = SHT_PROGBITS; 198 shdr->sh_addr = base_offset; 199 shdr->sh_flags = SHF_ALLOC; 200 shdr->sh_entsize = 0; 201 202 /* 203 * setup eh_frame_hdr section 204 */ 205 scn = elf_newscn(e); 206 if (!scn) { 207 warnx("cannot create section"); 208 return -1; 209 } 210 211 d = elf_newdata(scn); 212 if (!d) { 213 warnx("cannot get new data"); 214 return -1; 215 } 216 217 d->d_align = 4; 218 d->d_off = 0LL; 219 d->d_buf = unwinding + unwinding_table_size; 220 d->d_type = ELF_T_BYTE; 221 d->d_size = unwinding_header_size; 222 d->d_version = EV_CURRENT; 223 224 shdr = elf_getshdr(scn); 225 if (!shdr) { 226 warnx("cannot get section header"); 227 return -1; 228 } 229 230 shdr->sh_name = 90; 231 shdr->sh_type = SHT_PROGBITS; 232 shdr->sh_addr = base_offset + unwinding_table_size; 233 shdr->sh_flags = SHF_ALLOC; 234 shdr->sh_entsize = 0; 235 236 return 0; 237 } 238 239 /* 240 * fd: file descriptor open for writing for the output file 241 * load_addr: code load address (could be zero, just used for buildid) 242 * sym: function name (for native code - used as the symbol) 243 * code: the native code 244 * csize: the code size in bytes 245 */ 246 int 247 jit_write_elf(int fd, uint64_t load_addr, const char *sym, 248 const void *code, int csize, 249 void *debug __maybe_unused, int nr_debug_entries __maybe_unused, 250 void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size) 251 { 252 Elf *e; 253 Elf_Data *d; 254 Elf_Scn *scn; 255 Elf_Ehdr *ehdr; 256 Elf_Phdr *phdr; 257 Elf_Shdr *shdr; 258 uint64_t eh_frame_base_offset; 259 char *strsym = NULL; 260 int symlen; 261 int retval = -1; 262 263 if (elf_version(EV_CURRENT) == EV_NONE) { 264 warnx("ELF initialization failed"); 265 return -1; 266 } 267 268 e = elf_begin(fd, ELF_C_WRITE, NULL); 269 if (!e) { 270 warnx("elf_begin failed"); 271 goto error; 272 } 273 274 /* 275 * setup ELF header 276 */ 277 ehdr = elf_newehdr(e); 278 if (!ehdr) { 279 warnx("cannot get ehdr"); 280 goto error; 281 } 282 283 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN; 284 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS; 285 ehdr->e_machine = GEN_ELF_ARCH; 286 ehdr->e_type = ET_DYN; 287 ehdr->e_entry = GEN_ELF_TEXT_OFFSET; 288 ehdr->e_version = EV_CURRENT; 289 ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */ 290 291 /* 292 * setup program header 293 */ 294 phdr = elf_newphdr(e, 1); 295 phdr[0].p_type = PT_LOAD; 296 phdr[0].p_offset = 0; 297 phdr[0].p_vaddr = 0; 298 phdr[0].p_paddr = 0; 299 phdr[0].p_filesz = csize; 300 phdr[0].p_memsz = csize; 301 phdr[0].p_flags = PF_X | PF_R; 302 phdr[0].p_align = 8; 303 304 /* 305 * setup text section 306 */ 307 scn = elf_newscn(e); 308 if (!scn) { 309 warnx("cannot create section"); 310 goto error; 311 } 312 313 d = elf_newdata(scn); 314 if (!d) { 315 warnx("cannot get new data"); 316 goto error; 317 } 318 319 d->d_align = 16; 320 d->d_off = 0LL; 321 d->d_buf = (void *)code; 322 d->d_type = ELF_T_BYTE; 323 d->d_size = csize; 324 d->d_version = EV_CURRENT; 325 326 shdr = elf_getshdr(scn); 327 if (!shdr) { 328 warnx("cannot get section header"); 329 goto error; 330 } 331 332 shdr->sh_name = 1; 333 shdr->sh_type = SHT_PROGBITS; 334 shdr->sh_addr = GEN_ELF_TEXT_OFFSET; 335 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 336 shdr->sh_entsize = 0; 337 338 /* 339 * Setup .eh_frame_hdr and .eh_frame 340 */ 341 if (unwinding) { 342 eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize); 343 retval = jit_add_eh_frame_info(e, unwinding, 344 unwinding_header_size, unwinding_size, 345 eh_frame_base_offset); 346 if (retval) 347 goto error; 348 } 349 350 /* 351 * setup section headers string table 352 */ 353 scn = elf_newscn(e); 354 if (!scn) { 355 warnx("cannot create section"); 356 goto error; 357 } 358 359 d = elf_newdata(scn); 360 if (!d) { 361 warnx("cannot get new data"); 362 goto error; 363 } 364 365 d->d_align = 1; 366 d->d_off = 0LL; 367 d->d_buf = shd_string_table; 368 d->d_type = ELF_T_BYTE; 369 d->d_size = sizeof(shd_string_table); 370 d->d_version = EV_CURRENT; 371 372 shdr = elf_getshdr(scn); 373 if (!shdr) { 374 warnx("cannot get section header"); 375 goto error; 376 } 377 378 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */ 379 shdr->sh_type = SHT_STRTAB; 380 shdr->sh_flags = 0; 381 shdr->sh_entsize = 0; 382 383 /* 384 * setup symtab section 385 */ 386 symtab[1].st_size = csize; 387 symtab[1].st_value = GEN_ELF_TEXT_OFFSET; 388 389 scn = elf_newscn(e); 390 if (!scn) { 391 warnx("cannot create section"); 392 goto error; 393 } 394 395 d = elf_newdata(scn); 396 if (!d) { 397 warnx("cannot get new data"); 398 goto error; 399 } 400 401 d->d_align = 8; 402 d->d_off = 0LL; 403 d->d_buf = symtab; 404 d->d_type = ELF_T_SYM; 405 d->d_size = sizeof(symtab); 406 d->d_version = EV_CURRENT; 407 408 shdr = elf_getshdr(scn); 409 if (!shdr) { 410 warnx("cannot get section header"); 411 goto error; 412 } 413 414 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */ 415 shdr->sh_type = SHT_SYMTAB; 416 shdr->sh_flags = 0; 417 shdr->sh_entsize = sizeof(Elf_Sym); 418 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */ 419 420 /* 421 * setup symbols string table 422 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry 423 */ 424 symlen = 2 + strlen(sym); 425 strsym = calloc(1, symlen); 426 if (!strsym) { 427 warnx("cannot allocate strsym"); 428 goto error; 429 } 430 strcpy(strsym + 1, sym); 431 432 scn = elf_newscn(e); 433 if (!scn) { 434 warnx("cannot create section"); 435 goto error; 436 } 437 438 d = elf_newdata(scn); 439 if (!d) { 440 warnx("cannot get new data"); 441 goto error; 442 } 443 444 d->d_align = 1; 445 d->d_off = 0LL; 446 d->d_buf = strsym; 447 d->d_type = ELF_T_BYTE; 448 d->d_size = symlen; 449 d->d_version = EV_CURRENT; 450 451 shdr = elf_getshdr(scn); 452 if (!shdr) { 453 warnx("cannot get section header"); 454 goto error; 455 } 456 457 shdr->sh_name = 25; /* offset in shd_string_table */ 458 shdr->sh_type = SHT_STRTAB; 459 shdr->sh_flags = 0; 460 shdr->sh_entsize = 0; 461 462 /* 463 * setup build-id section 464 */ 465 scn = elf_newscn(e); 466 if (!scn) { 467 warnx("cannot create section"); 468 goto error; 469 } 470 471 d = elf_newdata(scn); 472 if (!d) { 473 warnx("cannot get new data"); 474 goto error; 475 } 476 477 /* 478 * build-id generation 479 */ 480 gen_build_id(&bnote, load_addr, code, csize); 481 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */ 482 bnote.desc.descsz = sizeof(bnote.build_id); 483 bnote.desc.type = NT_GNU_BUILD_ID; 484 strcpy(bnote.name, "GNU"); 485 486 d->d_align = 4; 487 d->d_off = 0LL; 488 d->d_buf = &bnote; 489 d->d_type = ELF_T_BYTE; 490 d->d_size = sizeof(bnote); 491 d->d_version = EV_CURRENT; 492 493 shdr = elf_getshdr(scn); 494 if (!shdr) { 495 warnx("cannot get section header"); 496 goto error; 497 } 498 499 shdr->sh_name = 33; /* offset in shd_string_table */ 500 shdr->sh_type = SHT_NOTE; 501 shdr->sh_addr = 0x0; 502 shdr->sh_flags = SHF_ALLOC; 503 shdr->sh_size = sizeof(bnote); 504 shdr->sh_entsize = 0; 505 506 #ifdef HAVE_DWARF_SUPPORT 507 if (debug && nr_debug_entries) { 508 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries); 509 if (retval) 510 goto error; 511 } else 512 #endif 513 { 514 if (elf_update(e, ELF_C_WRITE) < 0) { 515 warnx("elf_update 4 failed"); 516 goto error; 517 } 518 } 519 520 retval = 0; 521 error: 522 (void)elf_end(e); 523 524 free(strsym); 525 526 527 return retval; 528 } 529