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 <stdio.h>
12 #include <getopt.h>
13 #include <stddef.h>
14 #include <libelf.h>
15 #include <string.h>
16 #include <stdlib.h>
17 #include <unistd.h>
18 #include <inttypes.h>
19 #include <limits.h>
20 #include <fcntl.h>
21 #include <err.h>
22 #ifdef HAVE_DWARF_SUPPORT
23 #include <dwarf.h>
24 #endif
25
26 #include "genelf.h"
27 #include "../util/jitdump.h"
28 #include <linux/compiler.h>
29
30 #ifndef NT_GNU_BUILD_ID
31 #define NT_GNU_BUILD_ID 3
32 #endif
33
34 #define JVMTI
35
36 #define BUILD_ID_URANDOM /* different uuid for each run */
37
38 // FIXME, remove this and fix the deprecation warnings before its removed and
39 // We'll break for good here...
40 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
41
42 #ifdef HAVE_LIBCRYPTO_SUPPORT
43
44 #define BUILD_ID_MD5
45 #undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
46 #undef BUILD_ID_URANDOM /* different uuid for each run */
47
48 #ifdef BUILD_ID_SHA
49 #include <openssl/sha.h>
50 #endif
51
52 #ifdef BUILD_ID_MD5
53 #include <openssl/md5.h>
54 #endif
55 #endif
56
57
58 typedef struct {
59 unsigned int namesz; /* Size of entry's owner string */
60 unsigned int descsz; /* Size of the note descriptor */
61 unsigned int type; /* Interpretation of the descriptor */
62 char name[0]; /* Start of the name+desc data */
63 } Elf_Note;
64
65 struct options {
66 char *output;
67 int fd;
68 };
69
70 static char shd_string_table[] = {
71 0,
72 '.', 't', 'e', 'x', 't', 0, /* 1 */
73 '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */
74 '.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */
75 '.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */
76 '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
77 '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
78 '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
79 '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
80 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
81 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
82 };
83
84 static struct buildid_note {
85 Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */
86 char name[4]; /* GNU\0 */
87 char build_id[20];
88 } bnote;
89
90 static Elf_Sym symtab[]={
91 /* symbol 0 MUST be the undefined symbol */
92 { .st_name = 0, /* index in sym_string table */
93 .st_info = ELF_ST_TYPE(STT_NOTYPE),
94 .st_shndx = 0, /* for now */
95 .st_value = 0x0,
96 .st_other = ELF_ST_VIS(STV_DEFAULT),
97 .st_size = 0,
98 },
99 { .st_name = 1, /* index in sym_string table */
100 .st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
101 .st_shndx = 1,
102 .st_value = 0, /* for now */
103 .st_other = ELF_ST_VIS(STV_DEFAULT),
104 .st_size = 0, /* for now */
105 }
106 };
107
108 #ifdef BUILD_ID_URANDOM
109 static void
gen_build_id(struct buildid_note * note,unsigned long load_addr __maybe_unused,const void * code __maybe_unused,size_t csize __maybe_unused)110 gen_build_id(struct buildid_note *note,
111 unsigned long load_addr __maybe_unused,
112 const void *code __maybe_unused,
113 size_t csize __maybe_unused)
114 {
115 int fd;
116 size_t sz = sizeof(note->build_id);
117 ssize_t sret;
118
119 fd = open("/dev/urandom", O_RDONLY);
120 if (fd == -1)
121 err(1, "cannot access /dev/urandom for buildid");
122
123 sret = read(fd, note->build_id, sz);
124
125 close(fd);
126
127 if (sret != (ssize_t)sz)
128 memset(note->build_id, 0, sz);
129 }
130 #endif
131
132 #ifdef BUILD_ID_SHA
133 static void
gen_build_id(struct buildid_note * note,unsigned long load_addr __maybe_unused,const void * code,size_t csize)134 gen_build_id(struct buildid_note *note,
135 unsigned long load_addr __maybe_unused,
136 const void *code,
137 size_t csize)
138 {
139 if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
140 errx(1, "build_id too small for SHA1");
141
142 SHA1(code, csize, (unsigned char *)note->build_id);
143 }
144 #endif
145
146 #ifdef BUILD_ID_MD5
147 static void
gen_build_id(struct buildid_note * note,unsigned long load_addr,const void * code,size_t csize)148 gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
149 {
150 MD5_CTX context;
151
152 if (sizeof(note->build_id) < 16)
153 errx(1, "build_id too small for MD5");
154
155 MD5_Init(&context);
156 MD5_Update(&context, &load_addr, sizeof(load_addr));
157 MD5_Update(&context, code, csize);
158 MD5_Final((unsigned char *)note->build_id, &context);
159 }
160 #endif
161
162 static int
jit_add_eh_frame_info(Elf * e,void * unwinding,uint64_t unwinding_header_size,uint64_t unwinding_size,uint64_t base_offset)163 jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
164 uint64_t unwinding_size, uint64_t base_offset)
165 {
166 Elf_Data *d;
167 Elf_Scn *scn;
168 Elf_Shdr *shdr;
169 uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;
170
171 /*
172 * setup eh_frame section
173 */
174 scn = elf_newscn(e);
175 if (!scn) {
176 warnx("cannot create section");
177 return -1;
178 }
179
180 d = elf_newdata(scn);
181 if (!d) {
182 warnx("cannot get new data");
183 return -1;
184 }
185
186 d->d_align = 8;
187 d->d_off = 0LL;
188 d->d_buf = unwinding;
189 d->d_type = ELF_T_BYTE;
190 d->d_size = unwinding_table_size;
191 d->d_version = EV_CURRENT;
192
193 shdr = elf_getshdr(scn);
194 if (!shdr) {
195 warnx("cannot get section header");
196 return -1;
197 }
198
199 shdr->sh_name = 104;
200 shdr->sh_type = SHT_PROGBITS;
201 shdr->sh_addr = base_offset;
202 shdr->sh_flags = SHF_ALLOC;
203 shdr->sh_entsize = 0;
204
205 /*
206 * setup eh_frame_hdr section
207 */
208 scn = elf_newscn(e);
209 if (!scn) {
210 warnx("cannot create section");
211 return -1;
212 }
213
214 d = elf_newdata(scn);
215 if (!d) {
216 warnx("cannot get new data");
217 return -1;
218 }
219
220 d->d_align = 4;
221 d->d_off = 0LL;
222 d->d_buf = unwinding + unwinding_table_size;
223 d->d_type = ELF_T_BYTE;
224 d->d_size = unwinding_header_size;
225 d->d_version = EV_CURRENT;
226
227 shdr = elf_getshdr(scn);
228 if (!shdr) {
229 warnx("cannot get section header");
230 return -1;
231 }
232
233 shdr->sh_name = 90;
234 shdr->sh_type = SHT_PROGBITS;
235 shdr->sh_addr = base_offset + unwinding_table_size;
236 shdr->sh_flags = SHF_ALLOC;
237 shdr->sh_entsize = 0;
238
239 return 0;
240 }
241
242 /*
243 * fd: file descriptor open for writing for the output file
244 * load_addr: code load address (could be zero, just used for buildid)
245 * sym: function name (for native code - used as the symbol)
246 * code: the native code
247 * csize: the code size in bytes
248 */
249 int
jit_write_elf(int fd,uint64_t load_addr,const char * sym,const void * code,int csize,void * debug __maybe_unused,int nr_debug_entries __maybe_unused,void * unwinding,uint64_t unwinding_header_size,uint64_t unwinding_size)250 jit_write_elf(int fd, uint64_t load_addr, const char *sym,
251 const void *code, int csize,
252 void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
253 void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
254 {
255 Elf *e;
256 Elf_Data *d;
257 Elf_Scn *scn;
258 Elf_Ehdr *ehdr;
259 Elf_Phdr *phdr;
260 Elf_Shdr *shdr;
261 uint64_t eh_frame_base_offset;
262 char *strsym = NULL;
263 int symlen;
264 int retval = -1;
265
266 if (elf_version(EV_CURRENT) == EV_NONE) {
267 warnx("ELF initialization failed");
268 return -1;
269 }
270
271 e = elf_begin(fd, ELF_C_WRITE, NULL);
272 if (!e) {
273 warnx("elf_begin failed");
274 goto error;
275 }
276
277 /*
278 * setup ELF header
279 */
280 ehdr = elf_newehdr(e);
281 if (!ehdr) {
282 warnx("cannot get ehdr");
283 goto error;
284 }
285
286 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
287 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
288 ehdr->e_machine = GEN_ELF_ARCH;
289 ehdr->e_type = ET_DYN;
290 ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
291 ehdr->e_version = EV_CURRENT;
292 ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */
293
294 /*
295 * setup program header
296 */
297 phdr = elf_newphdr(e, 1);
298 phdr[0].p_type = PT_LOAD;
299 phdr[0].p_offset = GEN_ELF_TEXT_OFFSET;
300 phdr[0].p_vaddr = GEN_ELF_TEXT_OFFSET;
301 phdr[0].p_paddr = GEN_ELF_TEXT_OFFSET;
302 phdr[0].p_filesz = csize;
303 phdr[0].p_memsz = csize;
304 phdr[0].p_flags = PF_X | PF_R;
305 phdr[0].p_align = 8;
306
307 /*
308 * setup text section
309 */
310 scn = elf_newscn(e);
311 if (!scn) {
312 warnx("cannot create section");
313 goto error;
314 }
315
316 d = elf_newdata(scn);
317 if (!d) {
318 warnx("cannot get new data");
319 goto error;
320 }
321
322 d->d_align = 16;
323 d->d_off = 0LL;
324 d->d_buf = (void *)code;
325 d->d_type = ELF_T_BYTE;
326 d->d_size = csize;
327 d->d_version = EV_CURRENT;
328
329 shdr = elf_getshdr(scn);
330 if (!shdr) {
331 warnx("cannot get section header");
332 goto error;
333 }
334
335 shdr->sh_name = 1;
336 shdr->sh_type = SHT_PROGBITS;
337 shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
338 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
339 shdr->sh_entsize = 0;
340
341 /*
342 * Setup .eh_frame_hdr and .eh_frame
343 */
344 if (unwinding) {
345 eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
346 retval = jit_add_eh_frame_info(e, unwinding,
347 unwinding_header_size, unwinding_size,
348 eh_frame_base_offset);
349 if (retval)
350 goto error;
351 }
352
353 /*
354 * setup section headers string table
355 */
356 scn = elf_newscn(e);
357 if (!scn) {
358 warnx("cannot create section");
359 goto error;
360 }
361
362 d = elf_newdata(scn);
363 if (!d) {
364 warnx("cannot get new data");
365 goto error;
366 }
367
368 d->d_align = 1;
369 d->d_off = 0LL;
370 d->d_buf = shd_string_table;
371 d->d_type = ELF_T_BYTE;
372 d->d_size = sizeof(shd_string_table);
373 d->d_version = EV_CURRENT;
374
375 shdr = elf_getshdr(scn);
376 if (!shdr) {
377 warnx("cannot get section header");
378 goto error;
379 }
380
381 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
382 shdr->sh_type = SHT_STRTAB;
383 shdr->sh_flags = 0;
384 shdr->sh_entsize = 0;
385
386 /*
387 * setup symtab section
388 */
389 symtab[1].st_size = csize;
390 symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
391
392 scn = elf_newscn(e);
393 if (!scn) {
394 warnx("cannot create section");
395 goto error;
396 }
397
398 d = elf_newdata(scn);
399 if (!d) {
400 warnx("cannot get new data");
401 goto error;
402 }
403
404 d->d_align = 8;
405 d->d_off = 0LL;
406 d->d_buf = symtab;
407 d->d_type = ELF_T_SYM;
408 d->d_size = sizeof(symtab);
409 d->d_version = EV_CURRENT;
410
411 shdr = elf_getshdr(scn);
412 if (!shdr) {
413 warnx("cannot get section header");
414 goto error;
415 }
416
417 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
418 shdr->sh_type = SHT_SYMTAB;
419 shdr->sh_flags = 0;
420 shdr->sh_entsize = sizeof(Elf_Sym);
421 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
422
423 /*
424 * setup symbols string table
425 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
426 */
427 symlen = 2 + strlen(sym);
428 strsym = calloc(1, symlen);
429 if (!strsym) {
430 warnx("cannot allocate strsym");
431 goto error;
432 }
433 strcpy(strsym + 1, sym);
434
435 scn = elf_newscn(e);
436 if (!scn) {
437 warnx("cannot create section");
438 goto error;
439 }
440
441 d = elf_newdata(scn);
442 if (!d) {
443 warnx("cannot get new data");
444 goto error;
445 }
446
447 d->d_align = 1;
448 d->d_off = 0LL;
449 d->d_buf = strsym;
450 d->d_type = ELF_T_BYTE;
451 d->d_size = symlen;
452 d->d_version = EV_CURRENT;
453
454 shdr = elf_getshdr(scn);
455 if (!shdr) {
456 warnx("cannot get section header");
457 goto error;
458 }
459
460 shdr->sh_name = 25; /* offset in shd_string_table */
461 shdr->sh_type = SHT_STRTAB;
462 shdr->sh_flags = 0;
463 shdr->sh_entsize = 0;
464
465 /*
466 * setup build-id section
467 */
468 scn = elf_newscn(e);
469 if (!scn) {
470 warnx("cannot create section");
471 goto error;
472 }
473
474 d = elf_newdata(scn);
475 if (!d) {
476 warnx("cannot get new data");
477 goto error;
478 }
479
480 /*
481 * build-id generation
482 */
483 gen_build_id(&bnote, load_addr, code, csize);
484 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
485 bnote.desc.descsz = sizeof(bnote.build_id);
486 bnote.desc.type = NT_GNU_BUILD_ID;
487 strcpy(bnote.name, "GNU");
488
489 d->d_align = 4;
490 d->d_off = 0LL;
491 d->d_buf = &bnote;
492 d->d_type = ELF_T_BYTE;
493 d->d_size = sizeof(bnote);
494 d->d_version = EV_CURRENT;
495
496 shdr = elf_getshdr(scn);
497 if (!shdr) {
498 warnx("cannot get section header");
499 goto error;
500 }
501
502 shdr->sh_name = 33; /* offset in shd_string_table */
503 shdr->sh_type = SHT_NOTE;
504 shdr->sh_addr = 0x0;
505 shdr->sh_flags = SHF_ALLOC;
506 shdr->sh_size = sizeof(bnote);
507 shdr->sh_entsize = 0;
508
509 #ifdef HAVE_DWARF_SUPPORT
510 if (debug && nr_debug_entries) {
511 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
512 if (retval)
513 goto error;
514 } else
515 #endif
516 {
517 if (elf_update(e, ELF_C_WRITE) < 0) {
518 warnx("elf_update 4 failed");
519 goto error;
520 }
521 }
522
523 retval = 0;
524 error:
525 (void)elf_end(e);
526
527 free(strsym);
528
529
530 return retval;
531 }
532
533 #ifndef JVMTI
534
535 static unsigned char x86_code[] = {
536 0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
537 0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
538 0xCD, 0x80 /* int $0x80 */
539 };
540
541 static struct options options;
542
main(int argc,char ** argv)543 int main(int argc, char **argv)
544 {
545 int c, fd, ret;
546
547 while ((c = getopt(argc, argv, "o:h")) != -1) {
548 switch (c) {
549 case 'o':
550 options.output = optarg;
551 break;
552 case 'h':
553 printf("Usage: genelf -o output_file [-h]\n");
554 return 0;
555 default:
556 errx(1, "unknown option");
557 }
558 }
559
560 fd = open(options.output, O_CREAT|O_TRUNC|O_RDWR, 0666);
561 if (fd == -1)
562 err(1, "cannot create file %s", options.output);
563
564 ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
565 close(fd);
566
567 if (ret != 0)
568 unlink(options.output);
569
570 return ret;
571 }
572 #endif
573