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 struct options {
58 	char *output;
59 	int fd;
60 };
61 
62 static 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 
76 static 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 
82 static 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
101 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)102 gen_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
125 static void
gen_build_id(struct buildid_note * note,unsigned long load_addr __maybe_unused,const void * code,size_t csize)126 gen_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
139 static void
gen_build_id(struct buildid_note * note,unsigned long load_addr,const void * code,size_t csize)140 gen_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 
159 static int
jit_add_eh_frame_info(Elf * e,void * unwinding,uint64_t unwinding_header_size,uint64_t unwinding_size,uint64_t base_offset)160 jit_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  */
246 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)247 jit_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 = 0;
297 	phdr[0].p_vaddr = 0;
298 	phdr[0].p_paddr = 0;
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;
522 error:
523 	(void)elf_end(e);
524 
525 	free(strsym);
526 
527 
528 	return retval;
529 }
530