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_Shdr *shdr;
255 uint64_t eh_frame_base_offset;
256 char *strsym = NULL;
257 int symlen;
258 int retval = -1;
259
260 if (elf_version(EV_CURRENT) == EV_NONE) {
261 warnx("ELF initialization failed");
262 return -1;
263 }
264
265 e = elf_begin(fd, ELF_C_WRITE, NULL);
266 if (!e) {
267 warnx("elf_begin failed");
268 goto error;
269 }
270
271 /*
272 * setup ELF header
273 */
274 ehdr = elf_newehdr(e);
275 if (!ehdr) {
276 warnx("cannot get ehdr");
277 goto error;
278 }
279
280 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
281 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
282 ehdr->e_machine = GEN_ELF_ARCH;
283 ehdr->e_type = ET_DYN;
284 ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
285 ehdr->e_version = EV_CURRENT;
286 ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */
287
288 /*
289 * setup text section
290 */
291 scn = elf_newscn(e);
292 if (!scn) {
293 warnx("cannot create section");
294 goto error;
295 }
296
297 d = elf_newdata(scn);
298 if (!d) {
299 warnx("cannot get new data");
300 goto error;
301 }
302
303 d->d_align = 16;
304 d->d_off = 0LL;
305 d->d_buf = (void *)code;
306 d->d_type = ELF_T_BYTE;
307 d->d_size = csize;
308 d->d_version = EV_CURRENT;
309
310 shdr = elf_getshdr(scn);
311 if (!shdr) {
312 warnx("cannot get section header");
313 goto error;
314 }
315
316 shdr->sh_name = 1;
317 shdr->sh_type = SHT_PROGBITS;
318 shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
319 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
320 shdr->sh_entsize = 0;
321
322 /*
323 * Setup .eh_frame_hdr and .eh_frame
324 */
325 if (unwinding) {
326 eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
327 retval = jit_add_eh_frame_info(e, unwinding,
328 unwinding_header_size, unwinding_size,
329 eh_frame_base_offset);
330 if (retval)
331 goto error;
332 }
333
334 /*
335 * setup section headers string table
336 */
337 scn = elf_newscn(e);
338 if (!scn) {
339 warnx("cannot create section");
340 goto error;
341 }
342
343 d = elf_newdata(scn);
344 if (!d) {
345 warnx("cannot get new data");
346 goto error;
347 }
348
349 d->d_align = 1;
350 d->d_off = 0LL;
351 d->d_buf = shd_string_table;
352 d->d_type = ELF_T_BYTE;
353 d->d_size = sizeof(shd_string_table);
354 d->d_version = EV_CURRENT;
355
356 shdr = elf_getshdr(scn);
357 if (!shdr) {
358 warnx("cannot get section header");
359 goto error;
360 }
361
362 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
363 shdr->sh_type = SHT_STRTAB;
364 shdr->sh_flags = 0;
365 shdr->sh_entsize = 0;
366
367 /*
368 * setup symtab section
369 */
370 symtab[1].st_size = csize;
371 symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
372
373 scn = elf_newscn(e);
374 if (!scn) {
375 warnx("cannot create section");
376 goto error;
377 }
378
379 d = elf_newdata(scn);
380 if (!d) {
381 warnx("cannot get new data");
382 goto error;
383 }
384
385 d->d_align = 8;
386 d->d_off = 0LL;
387 d->d_buf = symtab;
388 d->d_type = ELF_T_SYM;
389 d->d_size = sizeof(symtab);
390 d->d_version = EV_CURRENT;
391
392 shdr = elf_getshdr(scn);
393 if (!shdr) {
394 warnx("cannot get section header");
395 goto error;
396 }
397
398 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
399 shdr->sh_type = SHT_SYMTAB;
400 shdr->sh_flags = 0;
401 shdr->sh_entsize = sizeof(Elf_Sym);
402 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
403
404 /*
405 * setup symbols string table
406 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
407 */
408 symlen = 2 + strlen(sym);
409 strsym = calloc(1, symlen);
410 if (!strsym) {
411 warnx("cannot allocate strsym");
412 goto error;
413 }
414 strcpy(strsym + 1, sym);
415
416 scn = elf_newscn(e);
417 if (!scn) {
418 warnx("cannot create section");
419 goto error;
420 }
421
422 d = elf_newdata(scn);
423 if (!d) {
424 warnx("cannot get new data");
425 goto error;
426 }
427
428 d->d_align = 1;
429 d->d_off = 0LL;
430 d->d_buf = strsym;
431 d->d_type = ELF_T_BYTE;
432 d->d_size = symlen;
433 d->d_version = EV_CURRENT;
434
435 shdr = elf_getshdr(scn);
436 if (!shdr) {
437 warnx("cannot get section header");
438 goto error;
439 }
440
441 shdr->sh_name = 25; /* offset in shd_string_table */
442 shdr->sh_type = SHT_STRTAB;
443 shdr->sh_flags = 0;
444 shdr->sh_entsize = 0;
445
446 /*
447 * setup build-id section
448 */
449 scn = elf_newscn(e);
450 if (!scn) {
451 warnx("cannot create section");
452 goto error;
453 }
454
455 d = elf_newdata(scn);
456 if (!d) {
457 warnx("cannot get new data");
458 goto error;
459 }
460
461 /*
462 * build-id generation
463 */
464 gen_build_id(&bnote, load_addr, code, csize);
465 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
466 bnote.desc.descsz = sizeof(bnote.build_id);
467 bnote.desc.type = NT_GNU_BUILD_ID;
468 strcpy(bnote.name, "GNU");
469
470 d->d_align = 4;
471 d->d_off = 0LL;
472 d->d_buf = &bnote;
473 d->d_type = ELF_T_BYTE;
474 d->d_size = sizeof(bnote);
475 d->d_version = EV_CURRENT;
476
477 shdr = elf_getshdr(scn);
478 if (!shdr) {
479 warnx("cannot get section header");
480 goto error;
481 }
482
483 shdr->sh_name = 33; /* offset in shd_string_table */
484 shdr->sh_type = SHT_NOTE;
485 shdr->sh_addr = 0x0;
486 shdr->sh_flags = SHF_ALLOC;
487 shdr->sh_size = sizeof(bnote);
488 shdr->sh_entsize = 0;
489
490 #ifdef HAVE_DWARF_SUPPORT
491 if (debug && nr_debug_entries) {
492 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
493 if (retval)
494 goto error;
495 } else
496 #endif
497 {
498 if (elf_update(e, ELF_C_WRITE) < 0) {
499 warnx("elf_update 4 failed");
500 goto error;
501 }
502 }
503
504 retval = 0;
505 error:
506 (void)elf_end(e);
507
508 free(strsym);
509
510
511 return retval;
512 }
513