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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
50typedef 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
57struct options {
58 char *output;
59 int fd;
60};
61
62static 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
76static 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
82static 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
101static void
102gen_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
125static void
126gen_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
139static void
140gen_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
159static int
160jit_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 */
246int
247jit_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 = GEN_ELF_TEXT_OFFSET;
297 phdr[0].p_vaddr = GEN_ELF_TEXT_OFFSET;
298 phdr[0].p_paddr = GEN_ELF_TEXT_OFFSET;
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 retval = -1;
349 }
350
351 /*
352 * setup section headers string table
353 */
354 scn = elf_newscn(e);
355 if (!scn) {
356 warnx("cannot create section");
357 goto error;
358 }
359
360 d = elf_newdata(scn);
361 if (!d) {
362 warnx("cannot get new data");
363 goto error;
364 }
365
366 d->d_align = 1;
367 d->d_off = 0LL;
368 d->d_buf = shd_string_table;
369 d->d_type = ELF_T_BYTE;
370 d->d_size = sizeof(shd_string_table);
371 d->d_version = EV_CURRENT;
372
373 shdr = elf_getshdr(scn);
374 if (!shdr) {
375 warnx("cannot get section header");
376 goto error;
377 }
378
379 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
380 shdr->sh_type = SHT_STRTAB;
381 shdr->sh_flags = 0;
382 shdr->sh_entsize = 0;
383
384 /*
385 * setup symtab section
386 */
387 symtab[1].st_size = csize;
388 symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
389
390 scn = elf_newscn(e);
391 if (!scn) {
392 warnx("cannot create section");
393 goto error;
394 }
395
396 d = elf_newdata(scn);
397 if (!d) {
398 warnx("cannot get new data");
399 goto error;
400 }
401
402 d->d_align = 8;
403 d->d_off = 0LL;
404 d->d_buf = symtab;
405 d->d_type = ELF_T_SYM;
406 d->d_size = sizeof(symtab);
407 d->d_version = EV_CURRENT;
408
409 shdr = elf_getshdr(scn);
410 if (!shdr) {
411 warnx("cannot get section header");
412 goto error;
413 }
414
415 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
416 shdr->sh_type = SHT_SYMTAB;
417 shdr->sh_flags = 0;
418 shdr->sh_entsize = sizeof(Elf_Sym);
419 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
420
421 /*
422 * setup symbols string table
423 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
424 */
425 symlen = 2 + strlen(sym);
426 strsym = calloc(1, symlen);
427 if (!strsym) {
428 warnx("cannot allocate strsym");
429 goto error;
430 }
431 strcpy(strsym + 1, sym);
432
433 scn = elf_newscn(e);
434 if (!scn) {
435 warnx("cannot create section");
436 goto error;
437 }
438
439 d = elf_newdata(scn);
440 if (!d) {
441 warnx("cannot get new data");
442 goto error;
443 }
444
445 d->d_align = 1;
446 d->d_off = 0LL;
447 d->d_buf = strsym;
448 d->d_type = ELF_T_BYTE;
449 d->d_size = symlen;
450 d->d_version = EV_CURRENT;
451
452 shdr = elf_getshdr(scn);
453 if (!shdr) {
454 warnx("cannot get section header");
455 goto error;
456 }
457
458 shdr->sh_name = 25; /* offset in shd_string_table */
459 shdr->sh_type = SHT_STRTAB;
460 shdr->sh_flags = 0;
461 shdr->sh_entsize = 0;
462
463 /*
464 * setup build-id section
465 */
466 scn = elf_newscn(e);
467 if (!scn) {
468 warnx("cannot create section");
469 goto error;
470 }
471
472 d = elf_newdata(scn);
473 if (!d) {
474 warnx("cannot get new data");
475 goto error;
476 }
477
478 /*
479 * build-id generation
480 */
481 gen_build_id(&bnote, load_addr, code, csize);
482 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
483 bnote.desc.descsz = sizeof(bnote.build_id);
484 bnote.desc.type = NT_GNU_BUILD_ID;
485 strcpy(bnote.name, "GNU");
486
487 d->d_align = 4;
488 d->d_off = 0LL;
489 d->d_buf = &bnote;
490 d->d_type = ELF_T_BYTE;
491 d->d_size = sizeof(bnote);
492 d->d_version = EV_CURRENT;
493
494 shdr = elf_getshdr(scn);
495 if (!shdr) {
496 warnx("cannot get section header");
497 goto error;
498 }
499
500 shdr->sh_name = 33; /* offset in shd_string_table */
501 shdr->sh_type = SHT_NOTE;
502 shdr->sh_addr = 0x0;
503 shdr->sh_flags = SHF_ALLOC;
504 shdr->sh_size = sizeof(bnote);
505 shdr->sh_entsize = 0;
506
507#ifdef HAVE_DWARF_SUPPORT
508 if (debug && nr_debug_entries) {
509 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
510 if (retval)
511 goto error;
512 } else
513#endif
514 {
515 if (elf_update(e, ELF_C_WRITE) < 0) {
516 warnx("elf_update 4 failed");
517 goto error;
518 }
519 }
520
521 retval = 0;
522error:
523 (void)elf_end(e);
524
525 free(strsym);
526
527
528 return retval;
529}