1/*
  2 * elf.c - ELF access library
  3 *
  4 * Adapted from kpatch (https://github.com/dynup/kpatch):
  5 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
  6 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
  7 *
  8 * This program is free software; you can redistribute it and/or
  9 * modify it under the terms of the GNU General Public License
 10 * as published by the Free Software Foundation; either version 2
 11 * of the License, or (at your option) any later version.
 12 *
 13 * This program is distributed in the hope that it will be useful,
 14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 16 * GNU General Public License for more details.
 17 *
 18 * You should have received a copy of the GNU General Public License
 19 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 20 */
 21
 22#include <sys/types.h>
 23#include <sys/stat.h>
 24#include <fcntl.h>
 25#include <stdio.h>
 26#include <stdlib.h>
 27#include <string.h>
 28#include <unistd.h>
 29
 30#include "elf.h"
 31#include "warn.h"
 32
 33/*
 34 * Fallback for systems without this "read, mmaping if possible" cmd.
 35 */
 36#ifndef ELF_C_READ_MMAP
 37#define ELF_C_READ_MMAP ELF_C_READ
 38#endif
 39
 40struct section *find_section_by_name(struct elf *elf, const char *name)
 41{
 42	struct section *sec;
 43
 44	list_for_each_entry(sec, &elf->sections, list)
 45		if (!strcmp(sec->name, name))
 46			return sec;
 47
 48	return NULL;
 49}
 50
 51static struct section *find_section_by_index(struct elf *elf,
 52					     unsigned int idx)
 53{
 54	struct section *sec;
 55
 56	list_for_each_entry(sec, &elf->sections, list)
 57		if (sec->idx == idx)
 58			return sec;
 59
 60	return NULL;
 61}
 62
 63static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 64{
 65	struct section *sec;
 66	struct symbol *sym;
 67
 68	list_for_each_entry(sec, &elf->sections, list)
 69		hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
 70			if (sym->idx == idx)
 71				return sym;
 72
 73	return NULL;
 74}
 75
 76struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
 77{
 78	struct symbol *sym;
 79
 80	list_for_each_entry(sym, &sec->symbol_list, list)
 81		if (sym->type != STT_SECTION &&
 82		    sym->offset == offset)
 83			return sym;
 84
 85	return NULL;
 86}
 87
 88struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
 89				     unsigned int len)
 90{
 91	struct rela *rela;
 92	unsigned long o;
 93
 94	if (!sec->rela)
 95		return NULL;
 96
 97	for (o = offset; o < offset + len; o++)
 98		hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
 99			if (rela->offset == o)
100				return rela;
101
102	return NULL;
103}
104
105struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
106{
107	return find_rela_by_dest_range(sec, offset, 1);
108}
109
110struct symbol *find_containing_func(struct section *sec, unsigned long offset)
111{
112	struct symbol *func;
113
114	list_for_each_entry(func, &sec->symbol_list, list)
115		if (func->type == STT_FUNC && offset >= func->offset &&
116		    offset < func->offset + func->len)
117			return func;
118
119	return NULL;
120}
121
122static int read_sections(struct elf *elf)
123{
124	Elf_Scn *s = NULL;
125	struct section *sec;
126	size_t shstrndx, sections_nr;
127	int i;
128
129	if (elf_getshdrnum(elf->elf, &sections_nr)) {
130		perror("elf_getshdrnum");
131		return -1;
132	}
133
134	if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
135		perror("elf_getshdrstrndx");
136		return -1;
137	}
138
139	for (i = 0; i < sections_nr; i++) {
140		sec = malloc(sizeof(*sec));
141		if (!sec) {
142			perror("malloc");
143			return -1;
144		}
145		memset(sec, 0, sizeof(*sec));
146
147		INIT_LIST_HEAD(&sec->symbol_list);
148		INIT_LIST_HEAD(&sec->rela_list);
149		hash_init(sec->rela_hash);
150		hash_init(sec->symbol_hash);
151
152		list_add_tail(&sec->list, &elf->sections);
153
154		s = elf_getscn(elf->elf, i);
155		if (!s) {
156			perror("elf_getscn");
157			return -1;
158		}
159
160		sec->idx = elf_ndxscn(s);
161
162		if (!gelf_getshdr(s, &sec->sh)) {
163			perror("gelf_getshdr");
164			return -1;
165		}
166
167		sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
168		if (!sec->name) {
169			perror("elf_strptr");
170			return -1;
171		}
172
173		sec->elf_data = elf_getdata(s, NULL);
174		if (!sec->elf_data) {
175			perror("elf_getdata");
176			return -1;
177		}
178
179		if (sec->elf_data->d_off != 0 ||
180		    sec->elf_data->d_size != sec->sh.sh_size) {
181			WARN("unexpected data attributes for %s", sec->name);
182			return -1;
183		}
184
185		sec->data = (unsigned long)sec->elf_data->d_buf;
186		sec->len = sec->elf_data->d_size;
187	}
188
189	/* sanity check, one more call to elf_nextscn() should return NULL */
190	if (elf_nextscn(elf->elf, s)) {
191		WARN("section entry mismatch");
192		return -1;
193	}
194
195	return 0;
196}
197
198static int read_symbols(struct elf *elf)
199{
200	struct section *symtab;
201	struct symbol *sym;
202	struct list_head *entry, *tmp;
203	int symbols_nr, i;
204
205	symtab = find_section_by_name(elf, ".symtab");
206	if (!symtab) {
207		WARN("missing symbol table");
208		return -1;
209	}
210
211	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
212
213	for (i = 0; i < symbols_nr; i++) {
214		sym = malloc(sizeof(*sym));
215		if (!sym) {
216			perror("malloc");
217			return -1;
218		}
219		memset(sym, 0, sizeof(*sym));
220
221		sym->idx = i;
222
223		if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
224			perror("gelf_getsym");
225			goto err;
226		}
227
228		sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
229				       sym->sym.st_name);
230		if (!sym->name) {
231			perror("elf_strptr");
232			goto err;
233		}
234
235		sym->type = GELF_ST_TYPE(sym->sym.st_info);
236		sym->bind = GELF_ST_BIND(sym->sym.st_info);
237
238		if (sym->sym.st_shndx > SHN_UNDEF &&
239		    sym->sym.st_shndx < SHN_LORESERVE) {
240			sym->sec = find_section_by_index(elf,
241							 sym->sym.st_shndx);
242			if (!sym->sec) {
243				WARN("couldn't find section for symbol %s",
244				     sym->name);
245				goto err;
246			}
247			if (sym->type == STT_SECTION) {
248				sym->name = sym->sec->name;
249				sym->sec->sym = sym;
250			}
251		} else
252			sym->sec = find_section_by_index(elf, 0);
253
254		sym->offset = sym->sym.st_value;
255		sym->len = sym->sym.st_size;
256
257		/* sorted insert into a per-section list */
258		entry = &sym->sec->symbol_list;
259		list_for_each_prev(tmp, &sym->sec->symbol_list) {
260			struct symbol *s;
261
262			s = list_entry(tmp, struct symbol, list);
263
264			if (sym->offset > s->offset) {
265				entry = tmp;
266				break;
267			}
268
269			if (sym->offset == s->offset && sym->len >= s->len) {
270				entry = tmp;
271				break;
272			}
273		}
274		list_add(&sym->list, entry);
275		hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
276	}
277
278	return 0;
279
280err:
281	free(sym);
282	return -1;
283}
284
285static int read_relas(struct elf *elf)
286{
287	struct section *sec;
288	struct rela *rela;
289	int i;
290	unsigned int symndx;
291
292	list_for_each_entry(sec, &elf->sections, list) {
293		if (sec->sh.sh_type != SHT_RELA)
294			continue;
295
296		sec->base = find_section_by_name(elf, sec->name + 5);
297		if (!sec->base) {
298			WARN("can't find base section for rela section %s",
299			     sec->name);
300			return -1;
301		}
302
303		sec->base->rela = sec;
304
305		for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
306			rela = malloc(sizeof(*rela));
307			if (!rela) {
308				perror("malloc");
309				return -1;
310			}
311			memset(rela, 0, sizeof(*rela));
312
313			if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
314				perror("gelf_getrela");
315				return -1;
316			}
317
318			rela->type = GELF_R_TYPE(rela->rela.r_info);
319			rela->addend = rela->rela.r_addend;
320			rela->offset = rela->rela.r_offset;
321			symndx = GELF_R_SYM(rela->rela.r_info);
322			rela->sym = find_symbol_by_index(elf, symndx);
323			if (!rela->sym) {
324				WARN("can't find rela entry symbol %d for %s",
325				     symndx, sec->name);
326				return -1;
327			}
328
329			list_add_tail(&rela->list, &sec->rela_list);
330			hash_add(sec->rela_hash, &rela->hash, rela->offset);
331
332		}
333	}
334
335	return 0;
336}
337
338struct elf *elf_open(const char *name)
339{
340	struct elf *elf;
341
342	elf_version(EV_CURRENT);
343
344	elf = malloc(sizeof(*elf));
345	if (!elf) {
346		perror("malloc");
347		return NULL;
348	}
349	memset(elf, 0, sizeof(*elf));
350
351	INIT_LIST_HEAD(&elf->sections);
352
353	elf->name = strdup(name);
354	if (!elf->name) {
355		perror("strdup");
356		goto err;
357	}
358
359	elf->fd = open(name, O_RDONLY);
360	if (elf->fd == -1) {
361		perror("open");
362		goto err;
363	}
364
365	elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
366	if (!elf->elf) {
367		perror("elf_begin");
368		goto err;
369	}
370
371	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
372		perror("gelf_getehdr");
373		goto err;
374	}
375
376	if (read_sections(elf))
377		goto err;
378
379	if (read_symbols(elf))
380		goto err;
381
382	if (read_relas(elf))
383		goto err;
384
385	return elf;
386
387err:
388	elf_close(elf);
389	return NULL;
390}
391
392void elf_close(struct elf *elf)
393{
394	struct section *sec, *tmpsec;
395	struct symbol *sym, *tmpsym;
396	struct rela *rela, *tmprela;
397
398	list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
399		list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
400			list_del(&sym->list);
401			hash_del(&sym->hash);
402			free(sym);
403		}
404		list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
405			list_del(&rela->list);
406			hash_del(&rela->hash);
407			free(rela);
408		}
409		list_del(&sec->list);
410		free(sec);
411	}
412	if (elf->name)
413		free(elf->name);
414	if (elf->fd > 0)
415		close(elf->fd);
416	if (elf->elf)
417		elf_end(elf->elf);
418	free(elf);
419}