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