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 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/md5.h> 45 #endif 46 #endif 47 48 49 typedef struct { 50 unsigned int namesz; /* Size of entry's owner string */ 51 unsigned int descsz; /* Size of the note descriptor */ 52 unsigned int type; /* Interpretation of the descriptor */ 53 char name[0]; /* Start of the name+desc data */ 54 } Elf_Note; 55 56 struct options { 57 char *output; 58 int fd; 59 }; 60 61 static char shd_string_table[] = { 62 0, 63 '.', 't', 'e', 'x', 't', 0, /* 1 */ 64 '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */ 65 '.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */ 66 '.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */ 67 '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */ 68 '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */ 69 '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */ 70 '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */ 71 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */ 72 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */ 73 }; 74 75 static struct buildid_note { 76 Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */ 77 char name[4]; /* GNU\0 */ 78 char build_id[20]; 79 } bnote; 80 81 static Elf_Sym symtab[]={ 82 /* symbol 0 MUST be the undefined symbol */ 83 { .st_name = 0, /* index in sym_string table */ 84 .st_info = ELF_ST_TYPE(STT_NOTYPE), 85 .st_shndx = 0, /* for now */ 86 .st_value = 0x0, 87 .st_other = ELF_ST_VIS(STV_DEFAULT), 88 .st_size = 0, 89 }, 90 { .st_name = 1, /* index in sym_string table */ 91 .st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC), 92 .st_shndx = 1, 93 .st_value = 0, /* for now */ 94 .st_other = ELF_ST_VIS(STV_DEFAULT), 95 .st_size = 0, /* for now */ 96 } 97 }; 98 99 #ifdef BUILD_ID_URANDOM 100 static void 101 gen_build_id(struct buildid_note *note, 102 unsigned long load_addr __maybe_unused, 103 const void *code __maybe_unused, 104 size_t csize __maybe_unused) 105 { 106 int fd; 107 size_t sz = sizeof(note->build_id); 108 ssize_t sret; 109 110 fd = open("/dev/urandom", O_RDONLY); 111 if (fd == -1) 112 err(1, "cannot access /dev/urandom for buildid"); 113 114 sret = read(fd, note->build_id, sz); 115 116 close(fd); 117 118 if (sret != (ssize_t)sz) 119 memset(note->build_id, 0, sz); 120 } 121 #endif 122 123 #ifdef BUILD_ID_SHA 124 static void 125 gen_build_id(struct buildid_note *note, 126 unsigned long load_addr __maybe_unused, 127 const void *code, 128 size_t csize) 129 { 130 if (sizeof(note->build_id) < SHA_DIGEST_LENGTH) 131 errx(1, "build_id too small for SHA1"); 132 133 SHA1(code, csize, (unsigned char *)note->build_id); 134 } 135 #endif 136 137 #ifdef BUILD_ID_MD5 138 static void 139 gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize) 140 { 141 MD5_CTX context; 142 143 if (sizeof(note->build_id) < 16) 144 errx(1, "build_id too small for MD5"); 145 146 MD5_Init(&context); 147 MD5_Update(&context, &load_addr, sizeof(load_addr)); 148 MD5_Update(&context, code, csize); 149 MD5_Final((unsigned char *)note->build_id, &context); 150 } 151 #endif 152 153 static int 154 jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size, 155 uint64_t unwinding_size, uint64_t base_offset) 156 { 157 Elf_Data *d; 158 Elf_Scn *scn; 159 Elf_Shdr *shdr; 160 uint64_t unwinding_table_size = unwinding_size - unwinding_header_size; 161 162 /* 163 * setup eh_frame section 164 */ 165 scn = elf_newscn(e); 166 if (!scn) { 167 warnx("cannot create section"); 168 return -1; 169 } 170 171 d = elf_newdata(scn); 172 if (!d) { 173 warnx("cannot get new data"); 174 return -1; 175 } 176 177 d->d_align = 8; 178 d->d_off = 0LL; 179 d->d_buf = unwinding; 180 d->d_type = ELF_T_BYTE; 181 d->d_size = unwinding_table_size; 182 d->d_version = EV_CURRENT; 183 184 shdr = elf_getshdr(scn); 185 if (!shdr) { 186 warnx("cannot get section header"); 187 return -1; 188 } 189 190 shdr->sh_name = 104; 191 shdr->sh_type = SHT_PROGBITS; 192 shdr->sh_addr = base_offset; 193 shdr->sh_flags = SHF_ALLOC; 194 shdr->sh_entsize = 0; 195 196 /* 197 * setup eh_frame_hdr section 198 */ 199 scn = elf_newscn(e); 200 if (!scn) { 201 warnx("cannot create section"); 202 return -1; 203 } 204 205 d = elf_newdata(scn); 206 if (!d) { 207 warnx("cannot get new data"); 208 return -1; 209 } 210 211 d->d_align = 4; 212 d->d_off = 0LL; 213 d->d_buf = unwinding + unwinding_table_size; 214 d->d_type = ELF_T_BYTE; 215 d->d_size = unwinding_header_size; 216 d->d_version = EV_CURRENT; 217 218 shdr = elf_getshdr(scn); 219 if (!shdr) { 220 warnx("cannot get section header"); 221 return -1; 222 } 223 224 shdr->sh_name = 90; 225 shdr->sh_type = SHT_PROGBITS; 226 shdr->sh_addr = base_offset + unwinding_table_size; 227 shdr->sh_flags = SHF_ALLOC; 228 shdr->sh_entsize = 0; 229 230 return 0; 231 } 232 233 /* 234 * fd: file descriptor open for writing for the output file 235 * load_addr: code load address (could be zero, just used for buildid) 236 * sym: function name (for native code - used as the symbol) 237 * code: the native code 238 * csize: the code size in bytes 239 */ 240 int 241 jit_write_elf(int fd, uint64_t load_addr, const char *sym, 242 const void *code, int csize, 243 void *debug __maybe_unused, int nr_debug_entries __maybe_unused, 244 void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size) 245 { 246 Elf *e; 247 Elf_Data *d; 248 Elf_Scn *scn; 249 Elf_Ehdr *ehdr; 250 Elf_Shdr *shdr; 251 uint64_t eh_frame_base_offset; 252 char *strsym = NULL; 253 int symlen; 254 int retval = -1; 255 256 if (elf_version(EV_CURRENT) == EV_NONE) { 257 warnx("ELF initialization failed"); 258 return -1; 259 } 260 261 e = elf_begin(fd, ELF_C_WRITE, NULL); 262 if (!e) { 263 warnx("elf_begin failed"); 264 goto error; 265 } 266 267 /* 268 * setup ELF header 269 */ 270 ehdr = elf_newehdr(e); 271 if (!ehdr) { 272 warnx("cannot get ehdr"); 273 goto error; 274 } 275 276 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN; 277 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS; 278 ehdr->e_machine = GEN_ELF_ARCH; 279 ehdr->e_type = ET_DYN; 280 ehdr->e_entry = GEN_ELF_TEXT_OFFSET; 281 ehdr->e_version = EV_CURRENT; 282 ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */ 283 284 /* 285 * setup text section 286 */ 287 scn = elf_newscn(e); 288 if (!scn) { 289 warnx("cannot create section"); 290 goto error; 291 } 292 293 d = elf_newdata(scn); 294 if (!d) { 295 warnx("cannot get new data"); 296 goto error; 297 } 298 299 d->d_align = 16; 300 d->d_off = 0LL; 301 d->d_buf = (void *)code; 302 d->d_type = ELF_T_BYTE; 303 d->d_size = csize; 304 d->d_version = EV_CURRENT; 305 306 shdr = elf_getshdr(scn); 307 if (!shdr) { 308 warnx("cannot get section header"); 309 goto error; 310 } 311 312 shdr->sh_name = 1; 313 shdr->sh_type = SHT_PROGBITS; 314 shdr->sh_addr = GEN_ELF_TEXT_OFFSET; 315 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 316 shdr->sh_entsize = 0; 317 318 /* 319 * Setup .eh_frame_hdr and .eh_frame 320 */ 321 if (unwinding) { 322 eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize); 323 retval = jit_add_eh_frame_info(e, unwinding, 324 unwinding_header_size, unwinding_size, 325 eh_frame_base_offset); 326 if (retval) 327 goto error; 328 } 329 330 /* 331 * setup section headers string table 332 */ 333 scn = elf_newscn(e); 334 if (!scn) { 335 warnx("cannot create section"); 336 goto error; 337 } 338 339 d = elf_newdata(scn); 340 if (!d) { 341 warnx("cannot get new data"); 342 goto error; 343 } 344 345 d->d_align = 1; 346 d->d_off = 0LL; 347 d->d_buf = shd_string_table; 348 d->d_type = ELF_T_BYTE; 349 d->d_size = sizeof(shd_string_table); 350 d->d_version = EV_CURRENT; 351 352 shdr = elf_getshdr(scn); 353 if (!shdr) { 354 warnx("cannot get section header"); 355 goto error; 356 } 357 358 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */ 359 shdr->sh_type = SHT_STRTAB; 360 shdr->sh_flags = 0; 361 shdr->sh_entsize = 0; 362 363 /* 364 * setup symtab section 365 */ 366 symtab[1].st_size = csize; 367 symtab[1].st_value = GEN_ELF_TEXT_OFFSET; 368 369 scn = elf_newscn(e); 370 if (!scn) { 371 warnx("cannot create section"); 372 goto error; 373 } 374 375 d = elf_newdata(scn); 376 if (!d) { 377 warnx("cannot get new data"); 378 goto error; 379 } 380 381 d->d_align = 8; 382 d->d_off = 0LL; 383 d->d_buf = symtab; 384 d->d_type = ELF_T_SYM; 385 d->d_size = sizeof(symtab); 386 d->d_version = EV_CURRENT; 387 388 shdr = elf_getshdr(scn); 389 if (!shdr) { 390 warnx("cannot get section header"); 391 goto error; 392 } 393 394 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */ 395 shdr->sh_type = SHT_SYMTAB; 396 shdr->sh_flags = 0; 397 shdr->sh_entsize = sizeof(Elf_Sym); 398 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */ 399 400 /* 401 * setup symbols string table 402 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry 403 */ 404 symlen = 2 + strlen(sym); 405 strsym = calloc(1, symlen); 406 if (!strsym) { 407 warnx("cannot allocate strsym"); 408 goto error; 409 } 410 strcpy(strsym + 1, sym); 411 412 scn = elf_newscn(e); 413 if (!scn) { 414 warnx("cannot create section"); 415 goto error; 416 } 417 418 d = elf_newdata(scn); 419 if (!d) { 420 warnx("cannot get new data"); 421 goto error; 422 } 423 424 d->d_align = 1; 425 d->d_off = 0LL; 426 d->d_buf = strsym; 427 d->d_type = ELF_T_BYTE; 428 d->d_size = symlen; 429 d->d_version = EV_CURRENT; 430 431 shdr = elf_getshdr(scn); 432 if (!shdr) { 433 warnx("cannot get section header"); 434 goto error; 435 } 436 437 shdr->sh_name = 25; /* offset in shd_string_table */ 438 shdr->sh_type = SHT_STRTAB; 439 shdr->sh_flags = 0; 440 shdr->sh_entsize = 0; 441 442 /* 443 * setup build-id section 444 */ 445 scn = elf_newscn(e); 446 if (!scn) { 447 warnx("cannot create section"); 448 goto error; 449 } 450 451 d = elf_newdata(scn); 452 if (!d) { 453 warnx("cannot get new data"); 454 goto error; 455 } 456 457 /* 458 * build-id generation 459 */ 460 gen_build_id(&bnote, load_addr, code, csize); 461 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */ 462 bnote.desc.descsz = sizeof(bnote.build_id); 463 bnote.desc.type = NT_GNU_BUILD_ID; 464 strcpy(bnote.name, "GNU"); 465 466 d->d_align = 4; 467 d->d_off = 0LL; 468 d->d_buf = &bnote; 469 d->d_type = ELF_T_BYTE; 470 d->d_size = sizeof(bnote); 471 d->d_version = EV_CURRENT; 472 473 shdr = elf_getshdr(scn); 474 if (!shdr) { 475 warnx("cannot get section header"); 476 goto error; 477 } 478 479 shdr->sh_name = 33; /* offset in shd_string_table */ 480 shdr->sh_type = SHT_NOTE; 481 shdr->sh_addr = 0x0; 482 shdr->sh_flags = SHF_ALLOC; 483 shdr->sh_size = sizeof(bnote); 484 shdr->sh_entsize = 0; 485 486 #ifdef HAVE_DWARF_SUPPORT 487 if (debug && nr_debug_entries) { 488 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries); 489 if (retval) 490 goto error; 491 } else 492 #endif 493 { 494 if (elf_update(e, ELF_C_WRITE) < 0) { 495 warnx("elf_update 4 failed"); 496 goto error; 497 } 498 } 499 500 retval = 0; 501 error: 502 (void)elf_end(e); 503 504 free(strsym); 505 506 507 return retval; 508 } 509