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
 33struct section *find_section_by_name(struct elf *elf, const char *name)
 34{
 35	struct section *sec;
 36
 37	list_for_each_entry(sec, &elf->sections, list)
 38		if (!strcmp(sec->name, name))
 39			return sec;
 40
 41	return NULL;
 42}
 43
 44static struct section *find_section_by_index(struct elf *elf,
 45					     unsigned int idx)
 46{
 47	struct section *sec;
 48
 49	list_for_each_entry(sec, &elf->sections, list)
 50		if (sec->idx == idx)
 51			return sec;
 52
 53	return NULL;
 54}
 55
 56static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 57{
 58	struct section *sec;
 59	struct symbol *sym;
 60
 61	list_for_each_entry(sec, &elf->sections, list)
 62		hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
 63			if (sym->idx == idx)
 64				return sym;
 65
 66	return NULL;
 67}
 68
 69struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
 70{
 71	struct symbol *sym;
 72
 73	list_for_each_entry(sym, &sec->symbol_list, list)
 74		if (sym->type != STT_SECTION &&
 75		    sym->offset == offset)
 76			return sym;
 77
 78	return NULL;
 79}
 80
 81struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
 82				     unsigned int len)
 83{
 84	struct rela *rela;
 85	unsigned long o;
 86
 87	if (!sec->rela)
 88		return NULL;
 89
 90	for (o = offset; o < offset + len; o++)
 91		hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
 92			if (rela->offset == o)
 93				return rela;
 94
 95	return NULL;
 96}
 97
 98struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
 99{
100	return find_rela_by_dest_range(sec, offset, 1);
101}
102
103struct symbol *find_containing_func(struct section *sec, unsigned long offset)
104{
105	struct symbol *func;
106
107	list_for_each_entry(func, &sec->symbol_list, list)
108		if (func->type == STT_FUNC && offset >= func->offset &&
109		    offset < func->offset + func->len)
110			return func;
111
112	return NULL;
113}
114
115static int read_sections(struct elf *elf)
116{
117	Elf_Scn *s = NULL;
118	struct section *sec;
119	size_t shstrndx, sections_nr;
120	int i;
121
122	if (elf_getshdrnum(elf->elf, &sections_nr)) {
123		perror("elf_getshdrnum");
124		return -1;
125	}
126
127	if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
128		perror("elf_getshdrstrndx");
129		return -1;
130	}
131
132	for (i = 0; i < sections_nr; i++) {
133		sec = malloc(sizeof(*sec));
134		if (!sec) {
135			perror("malloc");
136			return -1;
137		}
138		memset(sec, 0, sizeof(*sec));
139
140		INIT_LIST_HEAD(&sec->symbol_list);
141		INIT_LIST_HEAD(&sec->rela_list);
142		hash_init(sec->rela_hash);
143		hash_init(sec->symbol_hash);
144
145		list_add_tail(&sec->list, &elf->sections);
146
147		s = elf_getscn(elf->elf, i);
148		if (!s) {
149			perror("elf_getscn");
150			return -1;
151		}
152
153		sec->idx = elf_ndxscn(s);
154
155		if (!gelf_getshdr(s, &sec->sh)) {
156			perror("gelf_getshdr");
157			return -1;
158		}
159
160		sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
161		if (!sec->name) {
162			perror("elf_strptr");
163			return -1;
164		}
165
166		sec->elf_data = elf_getdata(s, NULL);
167		if (!sec->elf_data) {
168			perror("elf_getdata");
169			return -1;
170		}
171
172		if (sec->elf_data->d_off != 0 ||
173		    sec->elf_data->d_size != sec->sh.sh_size) {
174			WARN("unexpected data attributes for %s", sec->name);
175			return -1;
176		}
177
178		sec->data = (unsigned long)sec->elf_data->d_buf;
179		sec->len = sec->elf_data->d_size;
180	}
181
182	/* sanity check, one more call to elf_nextscn() should return NULL */
183	if (elf_nextscn(elf->elf, s)) {
184		WARN("section entry mismatch");
185		return -1;
186	}
187
188	return 0;
189}
190
191static int read_symbols(struct elf *elf)
192{
193	struct section *symtab;
194	struct symbol *sym;
195	struct list_head *entry, *tmp;
196	int symbols_nr, i;
197
198	symtab = find_section_by_name(elf, ".symtab");
199	if (!symtab) {
200		WARN("missing symbol table");
201		return -1;
202	}
203
204	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
205
206	for (i = 0; i < symbols_nr; i++) {
207		sym = malloc(sizeof(*sym));
208		if (!sym) {
209			perror("malloc");
210			return -1;
211		}
212		memset(sym, 0, sizeof(*sym));
213
214		sym->idx = i;
215
216		if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
217			perror("gelf_getsym");
218			goto err;
219		}
220
221		sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
222				       sym->sym.st_name);
223		if (!sym->name) {
224			perror("elf_strptr");
225			goto err;
226		}
227
228		sym->type = GELF_ST_TYPE(sym->sym.st_info);
229		sym->bind = GELF_ST_BIND(sym->sym.st_info);
230
231		if (sym->sym.st_shndx > SHN_UNDEF &&
232		    sym->sym.st_shndx < SHN_LORESERVE) {
233			sym->sec = find_section_by_index(elf,
234							 sym->sym.st_shndx);
235			if (!sym->sec) {
236				WARN("couldn't find section for symbol %s",
237				     sym->name);
238				goto err;
239			}
240			if (sym->type == STT_SECTION) {
241				sym->name = sym->sec->name;
242				sym->sec->sym = sym;
243			}
244		} else
245			sym->sec = find_section_by_index(elf, 0);
246
247		sym->offset = sym->sym.st_value;
248		sym->len = sym->sym.st_size;
249
250		/* sorted insert into a per-section list */
251		entry = &sym->sec->symbol_list;
252		list_for_each_prev(tmp, &sym->sec->symbol_list) {
253			struct symbol *s;
254
255			s = list_entry(tmp, struct symbol, list);
256
257			if (sym->offset > s->offset) {
258				entry = tmp;
259				break;
260			}
261
262			if (sym->offset == s->offset && sym->len >= s->len) {
263				entry = tmp;
264				break;
265			}
266		}
267		list_add(&sym->list, entry);
268		hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
269	}
270
271	return 0;
272
273err:
274	free(sym);
275	return -1;
276}
277
278static int read_relas(struct elf *elf)
279{
280	struct section *sec;
281	struct rela *rela;
282	int i;
283	unsigned int symndx;
284
285	list_for_each_entry(sec, &elf->sections, list) {
286		if (sec->sh.sh_type != SHT_RELA)
287			continue;
288
289		sec->base = find_section_by_name(elf, sec->name + 5);
290		if (!sec->base) {
291			WARN("can't find base section for rela section %s",
292			     sec->name);
293			return -1;
294		}
295
296		sec->base->rela = sec;
297
298		for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
299			rela = malloc(sizeof(*rela));
300			if (!rela) {
301				perror("malloc");
302				return -1;
303			}
304			memset(rela, 0, sizeof(*rela));
305
306			if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
307				perror("gelf_getrela");
308				return -1;
309			}
310
311			rela->type = GELF_R_TYPE(rela->rela.r_info);
312			rela->addend = rela->rela.r_addend;
313			rela->offset = rela->rela.r_offset;
314			symndx = GELF_R_SYM(rela->rela.r_info);
315			rela->sym = find_symbol_by_index(elf, symndx);
316			if (!rela->sym) {
317				WARN("can't find rela entry symbol %d for %s",
318				     symndx, sec->name);
319				return -1;
320			}
321
322			list_add_tail(&rela->list, &sec->rela_list);
323			hash_add(sec->rela_hash, &rela->hash, rela->offset);
324
325		}
326	}
327
328	return 0;
329}
330
331struct elf *elf_open(const char *name)
332{
333	struct elf *elf;
334
335	elf_version(EV_CURRENT);
336
337	elf = malloc(sizeof(*elf));
338	if (!elf) {
339		perror("malloc");
340		return NULL;
341	}
342	memset(elf, 0, sizeof(*elf));
343
344	INIT_LIST_HEAD(&elf->sections);
345
346	elf->name = strdup(name);
347	if (!elf->name) {
348		perror("strdup");
349		goto err;
350	}
351
352	elf->fd = open(name, O_RDONLY);
353	if (elf->fd == -1) {
354		perror("open");
355		goto err;
356	}
357
358	elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
359	if (!elf->elf) {
360		perror("elf_begin");
361		goto err;
362	}
363
364	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
365		perror("gelf_getehdr");
366		goto err;
367	}
368
369	if (read_sections(elf))
370		goto err;
371
372	if (read_symbols(elf))
373		goto err;
374
375	if (read_relas(elf))
376		goto err;
377
378	return elf;
379
380err:
381	elf_close(elf);
382	return NULL;
383}
384
385void elf_close(struct elf *elf)
386{
387	struct section *sec, *tmpsec;
388	struct symbol *sym, *tmpsym;
389	struct rela *rela, *tmprela;
390
391	list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
392		list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
393			list_del(&sym->list);
394			hash_del(&sym->hash);
395			free(sym);
396		}
397		list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
398			list_del(&rela->list);
399			hash_del(&rela->hash);
400			free(rela);
401		}
402		list_del(&sec->list);
403		free(sec);
404	}
405	if (elf->name)
406		free(elf->name);
407	if (elf->fd > 0)
408		close(elf->fd);
409	if (elf->elf)
410		elf_end(elf->elf);
411	free(elf);
412}