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