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