1 /* elf header parsing */
2 /* SPDX-License-Identifier: GPL-2.0-only */
3
4 #include <stdio.h>
5 #include <stdlib.h>
6 #include <string.h>
7
8 #include "elfparsing.h"
9 #include "common.h"
10 #include "cbfs.h"
11
12 /*
13 * Short form: this is complicated, but we've tried making it simple
14 * and we keep hitting problems with our ELF parsing.
15 *
16 * The ELF parsing situation has always been a bit tricky. In fact,
17 * we (and most others) have been getting it wrong in small ways for
18 * years. Recently this has caused real trouble for the ARM V8 build.
19 * In this file we attempt to finally get it right for all variations
20 * of endian-ness and word size and target architectures and
21 * architectures we might get run on. Phew!. To do this we borrow a
22 * page from the FreeBSD NFS xdr model (see elf_ehdr and elf_phdr),
23 * the Plan 9 endianness functions (see xdr.c), and Go interfaces (see
24 * how we use buffer structs in this file). This ends up being a bit
25 * wordy at the lowest level, but greatly simplifies the elf parsing
26 * code and removes a common source of bugs, namely, forgetting to
27 * flip type endianness when referencing a struct member.
28 *
29 * ELF files can have four combinations of data layout: 32/64, and
30 * big/little endian. Further, to add to the fun, depending on the
31 * word size, the size of the ELF structs varies. The coreboot SELF
32 * format is simpler in theory: it's supposed to be always BE, and the
33 * various struct members allow room for growth: the entry point is
34 * always 64 bits, for example, so the size of a SELF struct is
35 * constant, regardless of target architecture word size. Hence, we
36 * need to do some transformation of the ELF files.
37 *
38 * A given architecture, realistically, only supports one of the four
39 * combinations at a time as the 'native' format. Hence, our code has
40 * been sprinkled with every variation of [nh]to[hn][sll] over the
41 * years. We've never quite gotten it all right, however, and a quick
42 * pass over this code revealed another bug. It's all worked because,
43 * until now, all the working platforms that had CBFS were 32 LE. Even then,
44 * however, bugs crept in: we recently realized that we're not
45 * transforming the entry point to big format when we store into the
46 * SELF image.
47 *
48 * The problem is essentially an XDR operation:
49 * we have something in a foreign format and need to transform it.
50 * It's most like XDR because:
51 * 1) the byte order can be wrong
52 * 2) the word size can be wrong
53 * 3) the size of elements in the stream depends on the value
54 * of other elements in the stream
55 * it's not like XDR because:
56 * 1) the byte order can be right
57 * 2) the word size can be right
58 * 3) the struct members are all on a natural alignment
59 *
60 * Hence, this new approach. To cover word size issues, we *always*
61 * transform the two structs we care about, the file header and
62 * program header, into a native struct in the 64 bit format:
63 *
64 * [32,little] -> [Elf64_Ehdr, Elf64_Phdr]
65 * [64,little] -> [Elf64_Ehdr, Elf64_Phdr]
66 * [32,big] -> [Elf64_Ehdr, Elf64_Phdr]
67 * [64,big] -> [Elf64_Ehdr, Elf64_Phdr]
68 * Then we just use those structs, and all the need for inline ntoh* goes away,
69 * as well as all the chances for error.
70 * This works because all the SELF structs have fields large enough for
71 * the largest ELF 64 struct members, and all the Elf64 struct members
72 * are at least large enough for all ELF 32 struct members.
73 * We end up with one function to do all our ELF parsing, and two functions
74 * to transform the headers. For the put case, we also have
75 * XDR functions, and hopefully we'll never again spend 5 years with the
76 * wrong endian-ness on an output value :-)
77 * This should work for all word sizes and endianness we hope to target.
78 * I *really* don't want to be here for 128 bit addresses.
79 *
80 * The parse functions are called with a pointer to an input buffer
81 * struct. One might ask: are there enough bytes in the input buffer?
82 * We know there need to be at *least* sizeof(Elf32_Ehdr) +
83 * sizeof(Elf32_Phdr) bytes. Realistically, there has to be some data
84 * too. If we start to worry, though we have not in the past, we
85 * might apply the simple test: the input buffer needs to be at least
86 * sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) bytes because, even if it's
87 * ELF 32, there's got to be *some* data! This is not theoretically
88 * accurate but it is actually good enough in practice. It allows the
89 * header transformation code to ignore the possibility of underrun.
90 *
91 * We also must accommodate different ELF files, and hence formats,
92 * in the same cbfs invocation. We might load a 64-bit payload
93 * on a 32-bit machine; we might even have a mixed armv7/armv8
94 * SOC or even a system with an x86/ARM!
95 *
96 * A possibly problematic (though unlikely to be so) assumption
97 * is that we expect the BIOS to remain in the lowest 32 bits
98 * of the physical address space. Since ARMV8 has standardized
99 * on that, and x86_64 also has, this seems a safe assumption.
100 *
101 * To repeat, ELF structs are different sizes because ELF struct
102 * members are different sizes, depending on values in the ELF file
103 * header. For this we use the functions defined in xdr.c, which
104 * consume bytes, convert the endianness, and advance the data pointer
105 * in the buffer struct.
106 */
107
108
iself(const void * input)109 static int iself(const void *input)
110 {
111 const Elf32_Ehdr *ehdr = input;
112 return !memcmp(ehdr->e_ident, ELFMAG, 4);
113 }
114
115 /* Get the ident array, so we can figure out
116 * endian-ness, word size, and in future other useful
117 * parameters
118 */
119 static void
elf_eident(struct buffer * input,Elf64_Ehdr * ehdr)120 elf_eident(struct buffer *input, Elf64_Ehdr *ehdr)
121 {
122 bgets(input, ehdr->e_ident, sizeof(ehdr->e_ident));
123 }
124
125
126 static int
check_size(const struct buffer * b,size_t offset,size_t size,const char * desc)127 check_size(const struct buffer *b, size_t offset, size_t size, const char *desc)
128 {
129 if (size == 0)
130 return 0;
131
132 if (offset >= buffer_size(b) || (offset + size) > buffer_size(b)) {
133 ERROR("The file is not large enough for the '%s'. "
134 "%zu bytes @ offset %zu, input %zu bytes.\n",
135 desc, size, offset, buffer_size(b));
136 return -1;
137 }
138 return 0;
139 }
140
141 static void
elf_ehdr(struct buffer * input,Elf64_Ehdr * ehdr,struct xdr * xdr,int bit64)142 elf_ehdr(struct buffer *input, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64)
143 {
144 ehdr->e_type = xdr->get16(input);
145 ehdr->e_machine = xdr->get16(input);
146 ehdr->e_version = xdr->get32(input);
147 if (bit64){
148 ehdr->e_entry = xdr->get64(input);
149 ehdr->e_phoff = xdr->get64(input);
150 ehdr->e_shoff = xdr->get64(input);
151 } else {
152 ehdr->e_entry = xdr->get32(input);
153 ehdr->e_phoff = xdr->get32(input);
154 ehdr->e_shoff = xdr->get32(input);
155 }
156 ehdr->e_flags = xdr->get32(input);
157 ehdr->e_ehsize = xdr->get16(input);
158 ehdr->e_phentsize = xdr->get16(input);
159 ehdr->e_phnum = xdr->get16(input);
160 ehdr->e_shentsize = xdr->get16(input);
161 ehdr->e_shnum = xdr->get16(input);
162 ehdr->e_shstrndx = xdr->get16(input);
163 }
164
165 static void
elf_phdr(struct buffer * pinput,Elf64_Phdr * phdr,int entsize,struct xdr * xdr,int bit64)166 elf_phdr(struct buffer *pinput, Elf64_Phdr *phdr,
167 int entsize, struct xdr *xdr, int bit64)
168 {
169 /*
170 * The entsize need not be sizeof(*phdr).
171 * Hence, it is easier to keep a copy of the input,
172 * as the xdr functions may not advance the input
173 * pointer the full entsize; rather than get tricky
174 * we just advance it below.
175 */
176 struct buffer input;
177 buffer_clone(&input, pinput);
178 if (bit64){
179 phdr->p_type = xdr->get32(&input);
180 phdr->p_flags = xdr->get32(&input);
181 phdr->p_offset = xdr->get64(&input);
182 phdr->p_vaddr = xdr->get64(&input);
183 phdr->p_paddr = xdr->get64(&input);
184 phdr->p_filesz = xdr->get64(&input);
185 phdr->p_memsz = xdr->get64(&input);
186 phdr->p_align = xdr->get64(&input);
187 } else {
188 phdr->p_type = xdr->get32(&input);
189 phdr->p_offset = xdr->get32(&input);
190 phdr->p_vaddr = xdr->get32(&input);
191 phdr->p_paddr = xdr->get32(&input);
192 phdr->p_filesz = xdr->get32(&input);
193 phdr->p_memsz = xdr->get32(&input);
194 phdr->p_flags = xdr->get32(&input);
195 phdr->p_align = xdr->get32(&input);
196 }
197 buffer_seek(pinput, entsize);
198 }
199
200 static void
elf_shdr(struct buffer * pinput,Elf64_Shdr * shdr,int entsize,struct xdr * xdr,int bit64)201 elf_shdr(struct buffer *pinput, Elf64_Shdr *shdr,
202 int entsize, struct xdr *xdr, int bit64)
203 {
204 /*
205 * The entsize need not be sizeof(*shdr).
206 * Hence, it is easier to keep a copy of the input,
207 * as the xdr functions may not advance the input
208 * pointer the full entsize; rather than get tricky
209 * we just advance it below.
210 */
211 struct buffer input = *pinput;
212 if (bit64){
213 shdr->sh_name = xdr->get32(&input);
214 shdr->sh_type = xdr->get32(&input);
215 shdr->sh_flags = xdr->get64(&input);
216 shdr->sh_addr = xdr->get64(&input);
217 shdr->sh_offset = xdr->get64(&input);
218 shdr->sh_size= xdr->get64(&input);
219 shdr->sh_link = xdr->get32(&input);
220 shdr->sh_info = xdr->get32(&input);
221 shdr->sh_addralign = xdr->get64(&input);
222 shdr->sh_entsize = xdr->get64(&input);
223 } else {
224 shdr->sh_name = xdr->get32(&input);
225 shdr->sh_type = xdr->get32(&input);
226 shdr->sh_flags = xdr->get32(&input);
227 shdr->sh_addr = xdr->get32(&input);
228 shdr->sh_offset = xdr->get32(&input);
229 shdr->sh_size = xdr->get32(&input);
230 shdr->sh_link = xdr->get32(&input);
231 shdr->sh_info = xdr->get32(&input);
232 shdr->sh_addralign = xdr->get32(&input);
233 shdr->sh_entsize = xdr->get32(&input);
234 }
235 buffer_seek(pinput, entsize);
236 }
237
238 static int
phdr_read(const struct buffer * in,struct parsed_elf * pelf,struct xdr * xdr,int bit64)239 phdr_read(const struct buffer *in, struct parsed_elf *pelf,
240 struct xdr *xdr, int bit64)
241 {
242 struct buffer b;
243 Elf64_Phdr *phdr;
244 Elf64_Ehdr *ehdr;
245 int i;
246
247 ehdr = &pelf->ehdr;
248 /* cons up an input buffer for the headers.
249 * Note that the program headers can be anywhere,
250 * per the ELF spec, You'd be surprised how many ELF
251 * readers miss this little detail.
252 */
253 buffer_splice(&b, in, ehdr->e_phoff,
254 (uint32_t)ehdr->e_phentsize * ehdr->e_phnum);
255 if (check_size(in, ehdr->e_phoff, buffer_size(&b), "program headers"))
256 return -1;
257
258 /* gather up all the phdrs.
259 * We do them all at once because there is more
260 * than one loop over all the phdrs.
261 */
262 phdr = calloc(ehdr->e_phnum, sizeof(*phdr));
263 for (i = 0; i < ehdr->e_phnum; i++) {
264 DEBUG("Parsing segment %d\n", i);
265 elf_phdr(&b, &phdr[i], ehdr->e_phentsize, xdr, bit64);
266
267 /* Ensure the contents are valid within the elf file. */
268 if (check_size(in, phdr[i].p_offset, phdr[i].p_filesz,
269 "segment contents")) {
270 free(phdr);
271 return -1;
272 }
273 }
274
275 pelf->phdr = phdr;
276
277 return 0;
278 }
279
280 static int
shdr_read(const struct buffer * in,struct parsed_elf * pelf,struct xdr * xdr,int bit64)281 shdr_read(const struct buffer *in, struct parsed_elf *pelf,
282 struct xdr *xdr, int bit64)
283 {
284 struct buffer b;
285 Elf64_Shdr *shdr;
286 Elf64_Ehdr *ehdr;
287 int i;
288
289 ehdr = &pelf->ehdr;
290
291 /* cons up an input buffer for the section headers.
292 * Note that the section headers can be anywhere,
293 * per the ELF spec, You'd be surprised how many ELF
294 * readers miss this little detail.
295 */
296 buffer_splice(&b, in, ehdr->e_shoff,
297 (uint32_t)ehdr->e_shentsize * ehdr->e_shnum);
298 if (check_size(in, ehdr->e_shoff, buffer_size(&b), "section headers"))
299 return -1;
300
301 /* gather up all the shdrs. */
302 shdr = calloc(ehdr->e_shnum, sizeof(*shdr));
303 for (i = 0; i < ehdr->e_shnum; i++) {
304 DEBUG("Parsing section %d\n", i);
305 elf_shdr(&b, &shdr[i], ehdr->e_shentsize, xdr, bit64);
306 }
307
308 pelf->shdr = shdr;
309
310 return 0;
311 }
312
313 static int
reloc_read(const struct buffer * in,struct parsed_elf * pelf,struct xdr * xdr,int bit64)314 reloc_read(const struct buffer *in, struct parsed_elf *pelf,
315 struct xdr *xdr, int bit64)
316 {
317 struct buffer b;
318 Elf64_Word i;
319 Elf64_Ehdr *ehdr;
320
321 ehdr = &pelf->ehdr;
322 pelf->relocs = calloc(ehdr->e_shnum, sizeof(Elf64_Rela *));
323
324 /* Allocate array for each section that contains relocation entries. */
325 for (i = 0; i < ehdr->e_shnum; i++) {
326 Elf64_Shdr *shdr;
327 Elf64_Rela *rela;
328 Elf64_Xword j;
329 Elf64_Xword nrelocs;
330 int is_rela;
331
332 shdr = &pelf->shdr[i];
333
334 /* Only process REL and RELA sections. */
335 if (shdr->sh_type != SHT_REL && shdr->sh_type != SHT_RELA)
336 continue;
337
338 DEBUG("Checking relocation section %u\n", i);
339
340 /* Ensure the section that relocations apply is a valid. */
341 if (shdr->sh_info >= ehdr->e_shnum ||
342 shdr->sh_info == SHN_UNDEF) {
343 ERROR("Relocations apply to an invalid section: %u\n",
344 shdr[i].sh_info);
345 return -1;
346 }
347
348 is_rela = shdr->sh_type == SHT_RELA;
349
350 /* Determine the number relocations in this section. */
351 nrelocs = shdr->sh_size / shdr->sh_entsize;
352
353 pelf->relocs[i] = calloc(nrelocs, sizeof(Elf64_Rela));
354
355 buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size);
356 if (check_size(in, shdr->sh_offset, buffer_size(&b),
357 "relocation section")) {
358 ERROR("Relocation section %u failed.\n", i);
359 return -1;
360 }
361
362 rela = pelf->relocs[i];
363 for (j = 0; j < nrelocs; j++) {
364 if (bit64) {
365 rela->r_offset = xdr->get64(&b);
366 rela->r_info = xdr->get64(&b);
367 if (is_rela)
368 rela->r_addend = xdr->get64(&b);
369 } else {
370 uint32_t r_info;
371
372 rela->r_offset = xdr->get32(&b);
373 r_info = xdr->get32(&b);
374 rela->r_info = ELF64_R_INFO(ELF32_R_SYM(r_info),
375 ELF32_R_TYPE(r_info));
376 if (is_rela)
377 rela->r_addend = xdr->get32(&b);
378 }
379 rela++;
380 }
381 }
382
383 return 0;
384 }
385
strtab_read(const struct buffer * in,struct parsed_elf * pelf)386 static int strtab_read(const struct buffer *in, struct parsed_elf *pelf)
387 {
388 Elf64_Ehdr *ehdr;
389 Elf64_Word i;
390
391 ehdr = &pelf->ehdr;
392
393 if (ehdr->e_shstrndx >= ehdr->e_shnum) {
394 ERROR("Section header string table index out of range: %d\n",
395 ehdr->e_shstrndx);
396 return -1;
397 }
398
399 /* For each section of type SHT_STRTAB create a symtab buffer. */
400 pelf->strtabs = calloc(ehdr->e_shnum, sizeof(struct buffer *));
401
402 for (i = 0; i < ehdr->e_shnum; i++) {
403 struct buffer *b;
404 Elf64_Shdr *shdr = &pelf->shdr[i];
405
406 if (shdr->sh_type != SHT_STRTAB)
407 continue;
408
409 b = calloc(1, sizeof(*b));
410 buffer_splice(b, in, shdr->sh_offset, shdr->sh_size);
411 if (check_size(in, shdr->sh_offset, buffer_size(b), "strtab")) {
412 ERROR("STRTAB section not within bounds: %d\n", i);
413 free(b);
414 return -1;
415 }
416 pelf->strtabs[i] = b;
417 }
418
419 return 0;
420 }
421
422 static int
symtab_read(const struct buffer * in,struct parsed_elf * pelf,struct xdr * xdr,int bit64)423 symtab_read(const struct buffer *in, struct parsed_elf *pelf,
424 struct xdr *xdr, int bit64)
425 {
426 Elf64_Ehdr *ehdr;
427 Elf64_Shdr *shdr;
428 Elf64_Half shnum;
429 Elf64_Xword i;
430 Elf64_Xword nsyms;
431 Elf64_Sym *sym;
432 struct buffer b;
433
434 ehdr = &pelf->ehdr;
435
436 shdr = NULL;
437 for (shnum = 0; shnum < ehdr->e_shnum; shnum++) {
438 if (pelf->shdr[shnum].sh_type != SHT_SYMTAB)
439 continue;
440
441 if (shdr != NULL) {
442 ERROR("Multiple symbol sections found. %u and %u\n",
443 (unsigned int)(shdr - pelf->shdr), shnum);
444 return -1;
445 }
446
447 shdr = &pelf->shdr[shnum];
448 }
449
450 if (shdr == NULL) {
451 ERROR("No symbol table found.\n");
452 return -1;
453 }
454
455 buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size);
456 if (check_size(in, shdr->sh_offset, buffer_size(&b), "symtab"))
457 return -1;
458
459 nsyms = shdr->sh_size / shdr->sh_entsize;
460
461 pelf->syms = calloc(nsyms, sizeof(Elf64_Sym));
462
463 for (i = 0; i < nsyms; i++) {
464 sym = &pelf->syms[i];
465
466 if (bit64) {
467 sym->st_name = xdr->get32(&b);
468 sym->st_info = xdr->get8(&b);
469 sym->st_other = xdr->get8(&b);
470 sym->st_shndx = xdr->get16(&b);
471 sym->st_value = xdr->get64(&b);
472 sym->st_size = xdr->get64(&b);
473 } else {
474 sym->st_name = xdr->get32(&b);
475 sym->st_value = xdr->get32(&b);
476 sym->st_size = xdr->get32(&b);
477 sym->st_info = xdr->get8(&b);
478 sym->st_other = xdr->get8(&b);
479 sym->st_shndx = xdr->get16(&b);
480 }
481 }
482
483 return 0;
484 }
485
parse_elf(const struct buffer * pinput,struct parsed_elf * pelf,int flags)486 int parse_elf(const struct buffer *pinput, struct parsed_elf *pelf, int flags)
487 {
488 struct xdr *xdr = &xdr_le;
489 int bit64 = 0;
490 struct buffer input;
491 Elf64_Ehdr *ehdr;
492
493 /* Zero out the parsed elf structure. */
494 memset(pelf, 0, sizeof(*pelf));
495
496 if (!iself(buffer_get(pinput))) {
497 DEBUG("The stage file is not in ELF format!\n");
498 return -1;
499 }
500
501 buffer_clone(&input, pinput);
502 ehdr = &pelf->ehdr;
503 elf_eident(&input, ehdr);
504 bit64 = ehdr->e_ident[EI_CLASS] == ELFCLASS64;
505 /* Assume LE unless we are sure otherwise.
506 * We're not going to take on the task of
507 * fully validating the ELF file. That way
508 * lies madness.
509 */
510 if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
511 xdr = &xdr_be;
512
513 elf_ehdr(&input, ehdr, xdr, bit64);
514
515 /* Relocation processing requires section header parsing. */
516 if (flags & ELF_PARSE_RELOC)
517 flags |= ELF_PARSE_SHDR;
518
519 /* String table processing requires section header parsing. */
520 if (flags & ELF_PARSE_STRTAB)
521 flags |= ELF_PARSE_SHDR;
522
523 /* Symbole table processing requires section header parsing. */
524 if (flags & ELF_PARSE_SYMTAB)
525 flags |= ELF_PARSE_SHDR;
526
527 if ((flags & ELF_PARSE_PHDR) && phdr_read(pinput, pelf, xdr, bit64))
528 goto fail;
529
530 if ((flags & ELF_PARSE_SHDR) && shdr_read(pinput, pelf, xdr, bit64))
531 goto fail;
532
533 if ((flags & ELF_PARSE_RELOC) && reloc_read(pinput, pelf, xdr, bit64))
534 goto fail;
535
536 if ((flags & ELF_PARSE_STRTAB) && strtab_read(pinput, pelf))
537 goto fail;
538
539 if ((flags & ELF_PARSE_SYMTAB) && symtab_read(pinput, pelf, xdr, bit64))
540 goto fail;
541
542 return 0;
543
544 fail:
545 parsed_elf_destroy(pelf);
546 return -1;
547 }
548
parsed_elf_destroy(struct parsed_elf * pelf)549 void parsed_elf_destroy(struct parsed_elf *pelf)
550 {
551 Elf64_Half i;
552
553 free(pelf->phdr);
554 free(pelf->shdr);
555 if (pelf->relocs != NULL) {
556 for (i = 0; i < pelf->ehdr.e_shnum; i++)
557 free(pelf->relocs[i]);
558 }
559 free(pelf->relocs);
560
561 if (pelf->strtabs != NULL) {
562 for (i = 0; i < pelf->ehdr.e_shnum; i++)
563 free(pelf->strtabs[i]);
564 }
565 free(pelf->strtabs);
566 free(pelf->syms);
567 }
568
569 /* Get the headers from the buffer.
570 * Return -1 in the event of an error.
571 * The section headers are optional; if NULL
572 * is passed in for pshdr they won't be parsed.
573 * We don't (yet) make payload parsing optional
574 * because we've never seen a use case.
575 */
576 int
elf_headers(const struct buffer * pinput,Elf64_Ehdr * ehdr,Elf64_Phdr ** pphdr,Elf64_Shdr ** pshdr)577 elf_headers(const struct buffer *pinput,
578 Elf64_Ehdr *ehdr,
579 Elf64_Phdr **pphdr,
580 Elf64_Shdr **pshdr)
581 {
582 struct parsed_elf pelf;
583 int flags;
584
585 flags = ELF_PARSE_PHDR;
586
587 if (pshdr != NULL)
588 flags |= ELF_PARSE_SHDR;
589
590 if (parse_elf(pinput, &pelf, flags))
591 return -1;
592
593 /* Copy out the parsed elf header. */
594 memcpy(ehdr, &pelf.ehdr, sizeof(*ehdr));
595
596 *pphdr = calloc(ehdr->e_phnum, sizeof(Elf64_Phdr));
597 memcpy(*pphdr, pelf.phdr, ehdr->e_phnum * sizeof(Elf64_Phdr));
598
599 if (pshdr != NULL) {
600 *pshdr = calloc(ehdr->e_shnum, sizeof(Elf64_Shdr));
601 memcpy(*pshdr, pelf.shdr, ehdr->e_shnum * sizeof(Elf64_Shdr));
602 }
603
604 parsed_elf_destroy(&pelf);
605
606 return 0;
607 }
608
609 /* ELF Writing Support
610 *
611 * The ELF file is written according to the following layout:
612 * +------------------+
613 * | ELF Header |
614 * +------------------+
615 * | Section Headers |
616 * +------------------+
617 * | Program Headers |
618 * +------------------+
619 * | String table |
620 * +------------------+ <- 4KiB Aligned
621 * | Code/Data |
622 * +------------------+
623 */
624
elf_init_eheader(Elf64_Ehdr * ehdr,int machine,int nbits,int endian)625 void elf_init_eheader(Elf64_Ehdr *ehdr, int machine, int nbits, int endian)
626 {
627 memset(ehdr, 0, sizeof(*ehdr));
628 ehdr->e_ident[EI_MAG0] = ELFMAG0;
629 ehdr->e_ident[EI_MAG1] = ELFMAG1;
630 ehdr->e_ident[EI_MAG2] = ELFMAG2;
631 ehdr->e_ident[EI_MAG3] = ELFMAG3;
632 ehdr->e_ident[EI_CLASS] = nbits;
633 ehdr->e_ident[EI_DATA] = endian;
634 ehdr->e_ident[EI_VERSION] = EV_CURRENT;
635 ehdr->e_type = ET_EXEC;
636 ehdr->e_machine = machine;
637 ehdr->e_version = EV_CURRENT;
638 if (nbits == ELFCLASS64) {
639 ehdr->e_ehsize = sizeof(Elf64_Ehdr);
640 ehdr->e_phentsize = sizeof(Elf64_Phdr);
641 ehdr->e_shentsize = sizeof(Elf64_Shdr);
642 } else {
643 ehdr->e_ehsize = sizeof(Elf32_Ehdr);
644 ehdr->e_phentsize = sizeof(Elf32_Phdr);
645 ehdr->e_shentsize = sizeof(Elf32_Shdr);
646 }
647 }
648
649 /* Arbitrary maximum number of sections. */
650 #define MAX_SECTIONS 16
651 struct elf_writer_section {
652 Elf64_Shdr shdr;
653 struct buffer content;
654 const char *name;
655 };
656
657 struct elf_writer_string_table {
658 size_t next_offset;
659 size_t max_size;
660 char *buffer;
661 };
662
663 struct elf_writer_sym_table {
664 size_t max_entries;
665 size_t num_entries;
666 Elf64_Sym *syms;
667 };
668
669 #define MAX_REL_NAME 32
670 struct elf_writer_rel {
671 size_t num_entries;
672 size_t max_entries;
673 Elf64_Rel *rels;
674 struct elf_writer_section *sec;
675 char name[MAX_REL_NAME];
676 };
677
678 struct elf_writer
679 {
680 Elf64_Ehdr ehdr;
681 struct xdr *xdr;
682 size_t num_secs;
683 struct elf_writer_section sections[MAX_SECTIONS];
684 struct elf_writer_rel rel_sections[MAX_SECTIONS];
685 Elf64_Phdr *phdrs;
686 struct elf_writer_section *shstrtab_sec;
687 struct elf_writer_section *strtab_sec;
688 struct elf_writer_section *symtab_sec;
689 struct elf_writer_string_table strtab;
690 struct elf_writer_sym_table symtab;
691 int bit64;
692 };
693
section_index(struct elf_writer * ew,struct elf_writer_section * sec)694 static size_t section_index(struct elf_writer *ew,
695 struct elf_writer_section *sec)
696 {
697 return sec - &ew->sections[0];
698 }
699
last_section(struct elf_writer * ew)700 static struct elf_writer_section *last_section(struct elf_writer *ew)
701 {
702 return &ew->sections[ew->num_secs - 1];
703 }
704
strtab_init(struct elf_writer * ew,size_t size)705 static void strtab_init(struct elf_writer *ew, size_t size)
706 {
707 struct buffer b;
708 Elf64_Shdr shdr;
709
710 /* Start adding strings after the initial NUL entry. */
711 ew->strtab.next_offset = 1;
712 ew->strtab.max_size = size;
713 ew->strtab.buffer = calloc(1, ew->strtab.max_size);
714
715 buffer_init(&b, NULL, ew->strtab.buffer, ew->strtab.max_size);
716 memset(&shdr, 0, sizeof(shdr));
717 shdr.sh_type = SHT_STRTAB;
718 shdr.sh_addralign = 1;
719 shdr.sh_size = ew->strtab.max_size;
720 elf_writer_add_section(ew, &shdr, &b, ".strtab");
721 ew->strtab_sec = last_section(ew);
722 }
723
symtab_init(struct elf_writer * ew,size_t max_entries)724 static void symtab_init(struct elf_writer *ew, size_t max_entries)
725 {
726 struct buffer b;
727 Elf64_Shdr shdr;
728
729 memset(&shdr, 0, sizeof(shdr));
730 shdr.sh_type = SHT_SYMTAB;
731
732 if (ew->bit64) {
733 shdr.sh_entsize = sizeof(Elf64_Sym);
734 shdr.sh_addralign = sizeof(Elf64_Addr);
735 } else {
736 shdr.sh_entsize = sizeof(Elf32_Sym);
737 shdr.sh_addralign = sizeof(Elf32_Addr);
738 }
739
740 shdr.sh_size = shdr.sh_entsize * max_entries;
741
742 ew->symtab.syms = calloc(max_entries, sizeof(Elf64_Sym));
743 ew->symtab.num_entries = 1;
744 ew->symtab.max_entries = max_entries;
745
746 buffer_init(&b, NULL, ew->symtab.syms, shdr.sh_size);
747
748 elf_writer_add_section(ew, &shdr, &b, ".symtab");
749 ew->symtab_sec = last_section(ew);
750 }
751
elf_writer_init(const Elf64_Ehdr * ehdr)752 struct elf_writer *elf_writer_init(const Elf64_Ehdr *ehdr)
753 {
754 struct elf_writer *ew;
755 Elf64_Shdr shdr;
756 struct buffer empty_buffer;
757
758 if (!iself(ehdr))
759 return NULL;
760
761 ew = calloc(1, sizeof(*ew));
762
763 memcpy(&ew->ehdr, ehdr, sizeof(ew->ehdr));
764
765 ew->bit64 = ew->ehdr.e_ident[EI_CLASS] == ELFCLASS64;
766
767 /* Set the endinan ops. */
768 if (ew->ehdr.e_ident[EI_DATA] == ELFDATA2MSB)
769 ew->xdr = &xdr_be;
770 else
771 ew->xdr = &xdr_le;
772
773 /* Reset count and offsets */
774 ew->ehdr.e_phoff = 0;
775 ew->ehdr.e_shoff = 0;
776 ew->ehdr.e_shnum = 0;
777 ew->ehdr.e_phnum = 0;
778
779 memset(&empty_buffer, 0, sizeof(empty_buffer));
780 memset(&shdr, 0, sizeof(shdr));
781
782 /* Add SHT_NULL section header. */
783 shdr.sh_type = SHT_NULL;
784 elf_writer_add_section(ew, &shdr, &empty_buffer, NULL);
785
786 /* Add section header string table and maintain reference to it. */
787 shdr.sh_type = SHT_STRTAB;
788 elf_writer_add_section(ew, &shdr, &empty_buffer, ".shstrtab");
789 ew->shstrtab_sec = last_section(ew);
790 ew->ehdr.e_shstrndx = section_index(ew, ew->shstrtab_sec);
791
792 /* Add a small string table and symbol table. */
793 strtab_init(ew, 4096);
794 symtab_init(ew, 100);
795
796 return ew;
797 }
798
799 /*
800 * Clean up any internal state represented by ew. Aftewards the elf_writer
801 * is invalid.
802 * It is safe to call elf_writer_destroy with ew as NULL. It returns without
803 * performing any action.
804 */
elf_writer_destroy(struct elf_writer * ew)805 void elf_writer_destroy(struct elf_writer *ew)
806 {
807 int i;
808 if (ew == NULL)
809 return;
810 if (ew->phdrs != NULL)
811 free(ew->phdrs);
812 free(ew->strtab.buffer);
813 free(ew->symtab.syms);
814 for (i = 0; i < MAX_SECTIONS; i++)
815 free(ew->rel_sections[i].rels);
816 free(ew);
817 }
818
819 /*
820 * Add a section to the ELF file. Section type, flags, and memsize are
821 * maintained from the passed in Elf64_Shdr. The buffer represents the
822 * content of the section while the name is the name of section itself.
823 * Returns < 0 on error, 0 on success.
824 */
elf_writer_add_section(struct elf_writer * ew,const Elf64_Shdr * shdr,struct buffer * contents,const char * name)825 int elf_writer_add_section(struct elf_writer *ew, const Elf64_Shdr *shdr,
826 struct buffer *contents, const char *name)
827 {
828 struct elf_writer_section *newsh;
829
830 if (ew->num_secs == MAX_SECTIONS)
831 return -1;
832
833 newsh = &ew->sections[ew->num_secs];
834 ew->num_secs++;
835
836 memcpy(&newsh->shdr, shdr, sizeof(newsh->shdr));
837 newsh->shdr.sh_offset = 0;
838
839 newsh->name = name;
840 if (contents != NULL)
841 buffer_clone(&newsh->content, contents);
842
843 return 0;
844 }
845
ehdr_write(struct elf_writer * ew,struct buffer * m)846 static void ehdr_write(struct elf_writer *ew, struct buffer *m)
847 {
848 int i;
849
850 for (i = 0; i < EI_NIDENT; i++)
851 ew->xdr->put8(m, ew->ehdr.e_ident[i]);
852 ew->xdr->put16(m, ew->ehdr.e_type);
853 ew->xdr->put16(m, ew->ehdr.e_machine);
854 ew->xdr->put32(m, ew->ehdr.e_version);
855 if (ew->bit64) {
856 ew->xdr->put64(m, ew->ehdr.e_entry);
857 ew->xdr->put64(m, ew->ehdr.e_phoff);
858 ew->xdr->put64(m, ew->ehdr.e_shoff);
859 } else {
860 ew->xdr->put32(m, ew->ehdr.e_entry);
861 ew->xdr->put32(m, ew->ehdr.e_phoff);
862 ew->xdr->put32(m, ew->ehdr.e_shoff);
863 }
864 ew->xdr->put32(m, ew->ehdr.e_flags);
865 ew->xdr->put16(m, ew->ehdr.e_ehsize);
866 ew->xdr->put16(m, ew->ehdr.e_phentsize);
867 ew->xdr->put16(m, ew->ehdr.e_phnum);
868 ew->xdr->put16(m, ew->ehdr.e_shentsize);
869 ew->xdr->put16(m, ew->ehdr.e_shnum);
870 ew->xdr->put16(m, ew->ehdr.e_shstrndx);
871 }
872
shdr_write(struct elf_writer * ew,size_t n,struct buffer * m)873 static void shdr_write(struct elf_writer *ew, size_t n, struct buffer *m)
874 {
875 struct xdr *xdr = ew->xdr;
876 int bit64 = ew->bit64;
877 struct elf_writer_section *sec = &ew->sections[n];
878 Elf64_Shdr *shdr = &sec->shdr;
879
880 xdr->put32(m, shdr->sh_name);
881 xdr->put32(m, shdr->sh_type);
882 if (bit64) {
883 xdr->put64(m, shdr->sh_flags);
884 xdr->put64(m, shdr->sh_addr);
885 xdr->put64(m, shdr->sh_offset);
886 xdr->put64(m, shdr->sh_size);
887 xdr->put32(m, shdr->sh_link);
888 xdr->put32(m, shdr->sh_info);
889 xdr->put64(m, shdr->sh_addralign);
890 xdr->put64(m, shdr->sh_entsize);
891 } else {
892 xdr->put32(m, shdr->sh_flags);
893 xdr->put32(m, shdr->sh_addr);
894 xdr->put32(m, shdr->sh_offset);
895 xdr->put32(m, shdr->sh_size);
896 xdr->put32(m, shdr->sh_link);
897 xdr->put32(m, shdr->sh_info);
898 xdr->put32(m, shdr->sh_addralign);
899 xdr->put32(m, shdr->sh_entsize);
900 }
901 }
902
903 static void
phdr_write(struct elf_writer * ew,struct buffer * m,Elf64_Phdr * phdr)904 phdr_write(struct elf_writer *ew, struct buffer *m, Elf64_Phdr *phdr)
905 {
906 if (ew->bit64) {
907 ew->xdr->put32(m, phdr->p_type);
908 ew->xdr->put32(m, phdr->p_flags);
909 ew->xdr->put64(m, phdr->p_offset);
910 ew->xdr->put64(m, phdr->p_vaddr);
911 ew->xdr->put64(m, phdr->p_paddr);
912 ew->xdr->put64(m, phdr->p_filesz);
913 ew->xdr->put64(m, phdr->p_memsz);
914 ew->xdr->put64(m, phdr->p_align);
915 } else {
916 ew->xdr->put32(m, phdr->p_type);
917 ew->xdr->put32(m, phdr->p_offset);
918 ew->xdr->put32(m, phdr->p_vaddr);
919 ew->xdr->put32(m, phdr->p_paddr);
920 ew->xdr->put32(m, phdr->p_filesz);
921 ew->xdr->put32(m, phdr->p_memsz);
922 ew->xdr->put32(m, phdr->p_flags);
923 ew->xdr->put32(m, phdr->p_align);
924 }
925
926 }
927
section_consecutive(struct elf_writer * ew,Elf64_Half secidx)928 static int section_consecutive(struct elf_writer *ew, Elf64_Half secidx)
929 {
930 Elf64_Half i;
931 struct elf_writer_section *prev_alloc = NULL;
932
933 if (secidx == 0)
934 return 0;
935
936 for (i = 0; i < secidx; i++) {
937 if (ew->sections[i].shdr.sh_flags & SHF_ALLOC)
938 prev_alloc = &ew->sections[i];
939 }
940
941 if (prev_alloc == NULL)
942 return 0;
943
944 if (prev_alloc->shdr.sh_addr + prev_alloc->shdr.sh_size ==
945 ew->sections[secidx].shdr.sh_addr)
946 return 1;
947
948 return 0;
949 }
950
write_phdrs(struct elf_writer * ew,struct buffer * phdrs)951 static void write_phdrs(struct elf_writer *ew, struct buffer *phdrs)
952 {
953 Elf64_Half i;
954 Elf64_Phdr phdr;
955 size_t num_written = 0;
956 size_t num_needs_write = 0;
957
958 for (i = 0; i < ew->num_secs; i++) {
959 struct elf_writer_section *sec = &ew->sections[i];
960
961 if (!(sec->shdr.sh_flags & SHF_ALLOC))
962 continue;
963
964 if (!section_consecutive(ew, i)) {
965 /* Write out previously set phdr. */
966 if (num_needs_write != num_written) {
967 phdr_write(ew, phdrs, &phdr);
968 num_written++;
969 }
970 phdr.p_type = PT_LOAD;
971 phdr.p_offset = sec->shdr.sh_offset;
972 phdr.p_vaddr = sec->shdr.sh_addr;
973 phdr.p_paddr = sec->shdr.sh_addr;
974 phdr.p_filesz = buffer_size(&sec->content);
975 phdr.p_memsz = sec->shdr.sh_size;
976 phdr.p_flags = 0;
977 if (sec->shdr.sh_flags & SHF_EXECINSTR)
978 phdr.p_flags |= PF_X | PF_R;
979 if (sec->shdr.sh_flags & SHF_WRITE)
980 phdr.p_flags |= PF_W;
981 phdr.p_align = sec->shdr.sh_addralign;
982 num_needs_write++;
983
984 } else {
985 /* Accumulate file size and memsize. The assumption
986 * is that each section is either NOBITS or full
987 * (sh_size == file size). This is standard in that
988 * an ELF section doesn't have a file size component. */
989 if (sec->shdr.sh_flags & SHF_EXECINSTR)
990 phdr.p_flags |= PF_X | PF_R;
991 if (sec->shdr.sh_flags & SHF_WRITE)
992 phdr.p_flags |= PF_W;
993 phdr.p_filesz += buffer_size(&sec->content);
994 phdr.p_memsz += sec->shdr.sh_size;
995 }
996 }
997
998 /* Write out the last phdr. */
999 if (num_needs_write != num_written) {
1000 phdr_write(ew, phdrs, &phdr);
1001 num_written++;
1002 }
1003 assert(num_written == ew->ehdr.e_phnum);
1004 }
1005
fixup_symbol_table(struct elf_writer * ew)1006 static void fixup_symbol_table(struct elf_writer *ew)
1007 {
1008 struct elf_writer_section *sec = ew->symtab_sec;
1009
1010 /* If there is only the NULL section, mark section as inactive. */
1011 if (ew->symtab.num_entries == 1) {
1012 sec->shdr.sh_type = SHT_NULL;
1013 sec->shdr.sh_size = 0;
1014 } else {
1015 size_t i;
1016 struct buffer wr;
1017
1018 buffer_clone(&wr, &sec->content);
1019 /* To appease xdr. */
1020 buffer_set_size(&wr, 0);
1021 for (i = 0; i < ew->symtab.num_entries; i++) {
1022 /* Create local copy as were over-writing backing
1023 * store of the symbol. */
1024 Elf64_Sym sym = ew->symtab.syms[i];
1025 if (ew->bit64) {
1026 ew->xdr->put32(&wr, sym.st_name);
1027 ew->xdr->put8(&wr, sym.st_info);
1028 ew->xdr->put8(&wr, sym.st_other);
1029 ew->xdr->put16(&wr, sym.st_shndx);
1030 ew->xdr->put64(&wr, sym.st_value);
1031 ew->xdr->put64(&wr, sym.st_size);
1032 } else {
1033 ew->xdr->put32(&wr, sym.st_name);
1034 ew->xdr->put32(&wr, sym.st_value);
1035 ew->xdr->put32(&wr, sym.st_size);
1036 ew->xdr->put8(&wr, sym.st_info);
1037 ew->xdr->put8(&wr, sym.st_other);
1038 ew->xdr->put16(&wr, sym.st_shndx);
1039 }
1040 }
1041
1042 /* Update section size. */
1043 sec->shdr.sh_size = sec->shdr.sh_entsize;
1044 sec->shdr.sh_size *= ew->symtab.num_entries;
1045
1046 /* Fix up sh_link to point to string table. */
1047 sec->shdr.sh_link = section_index(ew, ew->strtab_sec);
1048 /* sh_info is supposed to be 1 greater than symbol table
1049 * index of last local binding. Just use max symbols. */
1050 sec->shdr.sh_info = ew->symtab.num_entries;
1051 }
1052
1053 buffer_set_size(&sec->content, sec->shdr.sh_size);
1054 }
1055
fixup_relocations(struct elf_writer * ew)1056 static void fixup_relocations(struct elf_writer *ew)
1057 {
1058 int i;
1059 Elf64_Xword type;
1060
1061 switch (ew->ehdr.e_machine) {
1062 case EM_386:
1063 type = R_386_32;
1064 break;
1065 case EM_X86_64:
1066 type = R_AMD64_64;
1067 break;
1068 case EM_ARM:
1069 type = R_ARM_ABS32;
1070 break;
1071 case EM_AARCH64:
1072 type = R_AARCH64_ABS64;
1073 break;
1074 case EM_MIPS:
1075 type = R_MIPS_32;
1076 break;
1077 case EM_RISCV:
1078 type = R_RISCV_32;
1079 break;
1080 case EM_PPC64:
1081 type = R_PPC64_ADDR32;
1082 break;
1083 default:
1084 ERROR("Unable to handle relocations for e_machine %x\n",
1085 ew->ehdr.e_machine);
1086 return;
1087 }
1088
1089 for (i = 0; i < MAX_SECTIONS; i++) {
1090 struct elf_writer_rel *rel_sec = &ew->rel_sections[i];
1091 struct elf_writer_section *sec = rel_sec->sec;
1092 struct buffer writer;
1093 size_t j;
1094
1095 if (sec == NULL)
1096 continue;
1097
1098 /* Update section header size as well as content size. */
1099 buffer_init(&sec->content, sec->content.name, rel_sec->rels,
1100 rel_sec->num_entries * sec->shdr.sh_entsize);
1101 sec->shdr.sh_size = buffer_size(&sec->content);
1102 buffer_clone(&writer, &sec->content);
1103 /* To make xdr happy. */
1104 buffer_set_size(&writer, 0);
1105
1106 for (j = 0; j < ew->rel_sections[i].num_entries; j++) {
1107 /* Make copy as we're overwriting backing store. */
1108 Elf64_Rel rel = rel_sec->rels[j];
1109 rel.r_info = ELF64_R_INFO(ELF64_R_SYM(rel.r_info),
1110 ELF64_R_TYPE(type));
1111
1112 if (ew->bit64) {
1113 ew->xdr->put64(&writer, rel.r_offset);
1114 ew->xdr->put64(&writer, rel.r_info);
1115 } else {
1116 Elf32_Rel rel32;
1117 rel32.r_offset = rel.r_offset;
1118 rel32.r_info =
1119 ELF32_R_INFO(ELF64_R_SYM(rel.r_info),
1120 ELF64_R_TYPE(rel.r_info));
1121 ew->xdr->put32(&writer, rel32.r_offset);
1122 ew->xdr->put32(&writer, rel32.r_info);
1123 }
1124 }
1125 }
1126 }
1127
1128 /*
1129 * Serialize the ELF file to the output buffer. Return < 0 on error,
1130 * 0 on success.
1131 */
elf_writer_serialize(struct elf_writer * ew,struct buffer * out)1132 int elf_writer_serialize(struct elf_writer *ew, struct buffer *out)
1133 {
1134 Elf64_Half i;
1135 Elf64_Xword metadata_size;
1136 Elf64_Xword program_size;
1137 Elf64_Off shstroffset;
1138 size_t shstrlen;
1139 struct buffer metadata;
1140 struct buffer phdrs;
1141 struct buffer data;
1142 struct buffer *strtab;
1143
1144 INFO("Writing %zu sections.\n", ew->num_secs);
1145
1146 /* Perform any necessary work for special sections. */
1147 fixup_symbol_table(ew);
1148 fixup_relocations(ew);
1149
1150 /* Determine size of sections to be written. */
1151 program_size = 0;
1152 /* Start with 1 byte for first byte of section header string table. */
1153 shstrlen = 1;
1154 for (i = 0; i < ew->num_secs; i++) {
1155 struct elf_writer_section *sec = &ew->sections[i];
1156
1157 if (sec->shdr.sh_flags & SHF_ALLOC) {
1158 if (!section_consecutive(ew, i))
1159 ew->ehdr.e_phnum++;
1160 }
1161
1162 program_size += buffer_size(&sec->content);
1163
1164 /* Keep track of the length sections' names. */
1165 if (sec->name != NULL) {
1166 sec->shdr.sh_name = shstrlen;
1167 shstrlen += strlen(sec->name) + 1;
1168 }
1169 }
1170 ew->ehdr.e_shnum = ew->num_secs;
1171 metadata_size = 0;
1172 metadata_size += ew->ehdr.e_ehsize;
1173 metadata_size += (Elf64_Xword)ew->ehdr.e_shnum * ew->ehdr.e_shentsize;
1174 metadata_size += (Elf64_Xword)ew->ehdr.e_phnum * ew->ehdr.e_phentsize;
1175 shstroffset = metadata_size;
1176 /* Align up section header string size and metadata size to 4KiB */
1177 metadata_size = ALIGN_UP(metadata_size + shstrlen, 4096);
1178
1179 if (buffer_create(out, metadata_size + program_size, "elfout")) {
1180 ERROR("Could not create output buffer for ELF.\n");
1181 return -1;
1182 }
1183
1184 INFO("Created %zu output buffer for ELF file.\n", buffer_size(out));
1185
1186 /*
1187 * Write out ELF header. Section headers come right after ELF header
1188 * followed by the program headers. Buffers need to be created first
1189 * to do the writing.
1190 */
1191 ew->ehdr.e_shoff = ew->ehdr.e_ehsize;
1192 ew->ehdr.e_phoff = ew->ehdr.e_shoff +
1193 (Elf64_Off)ew->ehdr.e_shnum * ew->ehdr.e_shentsize;
1194
1195 buffer_splice(&metadata, out, 0, metadata_size);
1196 buffer_splice(&phdrs, out, ew->ehdr.e_phoff,
1197 (uint32_t)ew->ehdr.e_phnum * ew->ehdr.e_phentsize);
1198 buffer_splice(&data, out, metadata_size, program_size);
1199 /* Set up the section header string table contents. */
1200 strtab = &ew->shstrtab_sec->content;
1201 buffer_splice(strtab, out, shstroffset, shstrlen);
1202 ew->shstrtab_sec->shdr.sh_size = shstrlen;
1203
1204 /* Reset current locations. */
1205 buffer_set_size(&metadata, 0);
1206 buffer_set_size(&data, 0);
1207 buffer_set_size(&phdrs, 0);
1208 buffer_set_size(strtab, 0);
1209
1210 /* ELF Header */
1211 ehdr_write(ew, &metadata);
1212
1213 /* Write out section headers, section strings, section content, and
1214 * program headers. */
1215 ew->xdr->put8(strtab, 0);
1216 for (i = 0; i < ew->num_secs; i++) {
1217 struct elf_writer_section *sec = &ew->sections[i];
1218
1219 /* Update section offsets. Be sure to not update SHN_UNDEF. */
1220 if (sec == ew->shstrtab_sec)
1221 sec->shdr.sh_offset = shstroffset;
1222 else if (i != SHN_UNDEF)
1223 sec->shdr.sh_offset = buffer_size(&data) +
1224 metadata_size;
1225
1226 shdr_write(ew, i, &metadata);
1227
1228 /* Add section name to string table. */
1229 if (sec->name != NULL)
1230 bputs(strtab, sec->name, strlen(sec->name) + 1);
1231
1232 /* Output section data for all sections but SHN_UNDEF and
1233 * section header string table. */
1234 if (i != SHN_UNDEF && sec != ew->shstrtab_sec)
1235 bputs(&data, buffer_get(&sec->content),
1236 buffer_size(&sec->content));
1237 }
1238
1239 write_phdrs(ew, &phdrs);
1240
1241 return 0;
1242 }
1243
1244 /* Add a string to the string table returning index on success, < 0 on error. */
elf_writer_add_string(struct elf_writer * ew,const char * new)1245 static int elf_writer_add_string(struct elf_writer *ew, const char *new)
1246 {
1247 size_t current_offset;
1248 size_t new_len;
1249
1250 for (current_offset = 0; current_offset < ew->strtab.next_offset; ) {
1251 const char *str = ew->strtab.buffer + current_offset;
1252 size_t len = strlen(str) + 1;
1253
1254 if (!strcmp(str, new))
1255 return current_offset;
1256 current_offset += len;
1257 }
1258
1259 new_len = strlen(new) + 1;
1260
1261 if (current_offset + new_len > ew->strtab.max_size) {
1262 ERROR("No space for string in .strtab.\n");
1263 return -1;
1264 }
1265
1266 memcpy(ew->strtab.buffer + current_offset, new, new_len);
1267 ew->strtab.next_offset = current_offset + new_len;
1268
1269 return current_offset;
1270 }
1271
elf_writer_section_index(struct elf_writer * ew,const char * name)1272 static int elf_writer_section_index(struct elf_writer *ew, const char *name)
1273 {
1274 size_t i;
1275
1276 for (i = 0; i < ew->num_secs; i++) {
1277 if (ew->sections[i].name == NULL)
1278 continue;
1279 if (!strcmp(ew->sections[i].name, name))
1280 return i;
1281 }
1282
1283 ERROR("ELF Section not found: %s\n", name);
1284
1285 return -1;
1286 }
1287
elf_writer_add_symbol(struct elf_writer * ew,const char * name,const char * section_name,Elf64_Addr value,Elf64_Word size,int binding,int type)1288 int elf_writer_add_symbol(struct elf_writer *ew, const char *name,
1289 const char *section_name,
1290 Elf64_Addr value, Elf64_Word size,
1291 int binding, int type)
1292 {
1293 int i;
1294 Elf64_Sym sym = {
1295 .st_value = value,
1296 .st_size = size,
1297 .st_info = ELF64_ST_INFO(binding, type),
1298 };
1299
1300 if (ew->symtab.max_entries == ew->symtab.num_entries) {
1301 ERROR("No more symbol entries left.\n");
1302 return -1;
1303 }
1304
1305 i = elf_writer_add_string(ew, name);
1306 if (i < 0)
1307 return -1;
1308 sym.st_name = i;
1309
1310 i = elf_writer_section_index(ew, section_name);
1311 if (i < 0)
1312 return -1;
1313 sym.st_shndx = i;
1314
1315 ew->symtab.syms[ew->symtab.num_entries++] = sym;
1316
1317 return 0;
1318 }
1319
elf_sym_index(struct elf_writer * ew,const char * sym)1320 static int elf_sym_index(struct elf_writer *ew, const char *sym)
1321 {
1322 int j;
1323 size_t i;
1324 Elf64_Word st_name;
1325
1326 /* Determine index of symbol in the string table. */
1327 j = elf_writer_add_string(ew, sym);
1328 if (j < 0)
1329 return -1;
1330
1331 st_name = j;
1332
1333 for (i = 0; i < ew->symtab.num_entries; i++)
1334 if (ew->symtab.syms[i].st_name == st_name)
1335 return i;
1336
1337 return -1;
1338 }
1339
rel_section(struct elf_writer * ew,const Elf64_Rel * r)1340 static struct elf_writer_rel *rel_section(struct elf_writer *ew,
1341 const Elf64_Rel *r)
1342 {
1343 Elf64_Sym *sym;
1344 struct elf_writer_rel *rel;
1345 Elf64_Shdr shdr;
1346 struct buffer b;
1347
1348 sym = &ew->symtab.syms[ELF64_R_SYM(r->r_info)];
1349
1350 /* Determine if section has been initialized yet. */
1351 rel = &ew->rel_sections[sym->st_shndx];
1352 if (rel->sec != NULL)
1353 return rel;
1354
1355 memset(&shdr, 0, sizeof(shdr));
1356 shdr.sh_type = SHT_REL;
1357 shdr.sh_link = section_index(ew, ew->symtab_sec);
1358 shdr.sh_info = sym->st_shndx;
1359
1360 if (ew->bit64) {
1361 shdr.sh_addralign = sizeof(Elf64_Addr);
1362 shdr.sh_entsize = sizeof(Elf64_Rel);
1363 } else {
1364 shdr.sh_addralign = sizeof(Elf32_Addr);
1365 shdr.sh_entsize = sizeof(Elf32_Rel);
1366 }
1367
1368 if ((strlen(".rel") + strlen(ew->sections[sym->st_shndx].name) + 1) >
1369 MAX_REL_NAME) {
1370 ERROR("Rel Section name won't fit\n");
1371 return NULL;
1372 }
1373
1374 strcat(rel->name, ".rel");
1375 strcat(rel->name, ew->sections[sym->st_shndx].name);
1376 buffer_init(&b, rel->name, NULL, 0);
1377
1378 elf_writer_add_section(ew, &shdr, &b, rel->name);
1379 rel->sec = last_section(ew);
1380
1381 return rel;
1382 }
1383
add_rel(struct elf_writer_rel * rel_sec,const Elf64_Rel * rel)1384 static int add_rel(struct elf_writer_rel *rel_sec, const Elf64_Rel *rel)
1385 {
1386 if (rel_sec->num_entries == rel_sec->max_entries) {
1387 size_t num = rel_sec->max_entries * 2;
1388 Elf64_Rel *old_rels;
1389
1390 if (num == 0)
1391 num = 128;
1392
1393 old_rels = rel_sec->rels;
1394 rel_sec->rels = calloc(num, sizeof(Elf64_Rel));
1395
1396 memcpy(rel_sec->rels, old_rels,
1397 rel_sec->num_entries * sizeof(Elf64_Rel));
1398 free(old_rels);
1399
1400 rel_sec->max_entries = num;
1401 }
1402
1403 rel_sec->rels[rel_sec->num_entries] = *rel;
1404 rel_sec->num_entries++;
1405
1406 return 0;
1407 }
1408
elf_writer_add_rel(struct elf_writer * ew,const char * sym,Elf64_Addr addr)1409 int elf_writer_add_rel(struct elf_writer *ew, const char *sym, Elf64_Addr addr)
1410 {
1411 Elf64_Rel rel;
1412 Elf64_Xword sym_info;
1413 int sym_index;
1414 struct elf_writer_rel *rel_sec;
1415
1416 sym_index = elf_sym_index(ew, sym);
1417
1418 if (sym_index < 0) {
1419 ERROR("Unable to locate symbol: %s\n", sym);
1420 return -1;
1421 }
1422
1423 sym_info = sym_index;
1424
1425 /* The relocation type will get fixed prior to serialization. */
1426 rel.r_offset = addr;
1427 rel.r_info = ELF64_R_INFO(sym_info, 0);
1428
1429 rel_sec = rel_section(ew, &rel);
1430
1431 if (rel_sec == NULL)
1432 return -1;
1433
1434 return add_rel(rel_sec, &rel);
1435 }
1436
elf_program_file_size_align(const struct buffer * input,size_t * file_size,size_t * align)1437 int elf_program_file_size_align(const struct buffer *input, size_t *file_size, size_t *align)
1438 {
1439 Elf64_Ehdr ehdr;
1440 Elf64_Phdr *phdr;
1441 int i;
1442 size_t loadable_file_size = 0;
1443 size_t align_size = 0;
1444
1445 if (elf_headers(input, &ehdr, &phdr, NULL))
1446 return -1;
1447
1448 for (i = 0; i < ehdr.e_phnum; i++) {
1449 if (phdr[i].p_type != PT_LOAD)
1450 continue;
1451 loadable_file_size += phdr[i].p_filesz;
1452 align_size = MAX(align_size, phdr[i].p_align);
1453 }
1454
1455 *file_size = loadable_file_size;
1456 *align = align_size;
1457
1458 free(phdr);
1459
1460 return 0;
1461 }
1462