aboutsummaryrefslogtreecommitdiff
path: root/elf/dl-load.c
blob: 416f9ac6882578eb192bbb17d5b421ba455791ce (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
/* _dl_map_object -- Map in a shared object's segments from the file.
Copyright (C) 1995, 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <link.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include "dynamic-link.h"


/* On some systems, no flag bits are given to specify file mapping.  */
#ifndef MAP_FILE
#define MAP_FILE	0
#endif

/* The right way to map in the shared library files is MAP_COPY, which
   makes a virtual copy of the data at the time of the mmap call; this
   guarantees the mapped pages will be consistent even if the file is
   overwritten.  Some losing VM systems like Linux's lack MAP_COPY.  All we
   get is MAP_PRIVATE, which copies each page when it is modified; this
   means if the file is overwritten, we may at some point get some pages
   from the new version after starting with pages from the old version.  */
#ifndef MAP_COPY
#define MAP_COPY	MAP_PRIVATE
#endif


#include <endian.h>
#if BYTE_ORDER == BIG_ENDIAN
#define byteorder ELFDATA2MSB
#define byteorder_name "big-endian"
#elif BYTE_ORDER == LITTLE_ENDIAN
#define byteorder ELFDATA2LSB
#define byteorder_name "little-endian"
#else
#error "Unknown BYTE_ORDER " BYTE_ORDER
#define byteorder ELFDATANONE
#endif

#define STRING(x) #x

int _dl_zerofd = -1;


/* Try to open NAME in one of the directories in DIRPATH.
   Return the fd, or -1.  If successful, fill in *REALNAME
   with the malloc'd full directory name.  */

static int
open_path (const char *name, size_t namelen,
	   const char *dirpath,
	   char **realname)
{
  char *buf;
  const char *p;
  int fd;

  p = dirpath;
  if (p == NULL || *p == '\0')
    {
      errno = ENOENT;
      return -1;
    }

  buf = alloca (strlen (dirpath) + 1 + namelen);
  do
    {
      dirpath = p;
      p = strpbrk (dirpath, ":;");
      if (p == NULL)
	p = strchr (dirpath, '\0');

      if (p == dirpath)
	/* Two adjacent colons, or a colon at the beginning or the end of
	   the path means to search the current directory.  */
	(void) memcpy (buf, name, namelen);
      else
	{
	  /* Construct the pathname to try.  */
	  (void) memcpy (buf, dirpath, p - dirpath);
	  buf[p - dirpath] = '/';
	  (void) memcpy (&buf[(p - dirpath) + 1], name, namelen);
	}

      fd = open (buf, O_RDONLY);
      if (fd != -1)
	{
	  *realname = strdup (buf);
	  return fd;
	}
      if (errno != ENOENT && errno != EACCES)
	/* The file exists and is readable, but something went wrong.  */
	return -1;
    }
  while (*p++ != '\0');

  return -1;
}


/* Map in the shared object file NAME.  */

struct link_map *
_dl_map_object (struct link_map *loader, const char *name)
{
  int fd;
  char *realname;
  struct link_map *l;

  /* Look for this name among those already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (name, l->l_libname))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	++l->l_opencount;
	return l;
      }

  if (strchr (name, '/') == NULL)
    {
      /* Search for NAME in several places.  */

      size_t namelen = strlen (name) + 1;

      inline void trypath (const char *dirpath)
	{
	  fd = open_path (name, namelen, dirpath, &realname);
	}

      fd = -1;
      if (loader && loader->l_info[DT_RPATH])
	trypath ((const char *) (loader->l_addr +
				 loader->l_info[DT_STRTAB]->d_un.d_ptr +
				 loader->l_info[DT_RPATH]->d_un.d_val));
      if (fd == -1 && ! _dl_secure)
	trypath (getenv ("LD_LIBRARY_PATH"));
      if (fd == -1)
	{
	  extern const char *_dl_rpath;	/* Set in rtld.c. */
	  trypath (_dl_rpath);
	}
    }
  else
    {
      fd = open (name, O_RDONLY);
      if (fd != -1)
	realname = strdup (name);
    }

  if (fd == -1)
    _dl_signal_error (errno, name, "cannot open shared object file");

  return _dl_map_object_from_fd (name, fd, realname);
}


/* Map in the shared object NAME, actually located in REALNAME, and already
   opened on FD.  */

struct link_map *
_dl_map_object_from_fd (const char *name, int fd, char *realname)
{
  struct link_map *l = NULL;
  const size_t pagesize = getpagesize ();
  void *file_mapping = NULL;
  size_t mapping_size = 0;

#define LOSE(s) lose (0, (s))
  void lose (int code, const char *msg)
    {
      (void) close (fd);
      if (file_mapping)
	munmap (file_mapping, mapping_size);
      _dl_signal_error (code, l ? l->l_name : name, msg);
    }

  inline caddr_t map_segment (Elf32_Addr mapstart, size_t len,
			      int prot, int fixed, off_t offset)
    {
      caddr_t mapat = mmap ((caddr_t) mapstart, len, prot,
			    fixed|MAP_COPY|MAP_FILE,
			    fd, offset);
      if (mapat == (caddr_t) -1)
	lose (errno, "failed to map segment from shared object");
      return mapat;
    }

  /* Make sure LOCATION is mapped in.  */
  void *map (off_t location, size_t size)
    {
      if ((off_t) mapping_size <= location + (off_t) size)
	{
	  void *result;
	  if (file_mapping)
	    munmap (file_mapping, mapping_size);
	  mapping_size = (location + size + 1 + pagesize - 1);
	  mapping_size &= ~(pagesize - 1);
	  result = mmap (file_mapping, mapping_size, PROT_READ,
			 MAP_COPY|MAP_FILE, fd, 0);
	  if (result == (void *) -1)
	    lose (errno, "cannot map file data");
	  file_mapping = result;
	}
      return file_mapping + location;
    }

  const Elf32_Ehdr *header;
  const Elf32_Phdr *phdr;
  const Elf32_Phdr *ph;
  int type;

  /* Look again to see if the real name matched another already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (realname, l->l_name))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	close (fd);
	free (realname);
	++l->l_opencount;
	return l;
      }

  /* Map in the first page to read the header.  */
  header = map (0, sizeof *header);

  /* Check the header for basic validity.  */
  if (*(Elf32_Word *) &header->e_ident !=
#if BYTE_ORDER == LITTLE_ENDIAN
      ((ELFMAG0 << (EI_MAG0 * 8)) |
       (ELFMAG1 << (EI_MAG1 * 8)) |
       (ELFMAG2 << (EI_MAG2 * 8)) |
       (ELFMAG3 << (EI_MAG3 * 8)))
#else
      ((ELFMAG0 << (EI_MAG3 * 8)) |
       (ELFMAG1 << (EI_MAG2 * 8)) |
       (ELFMAG2 << (EI_MAG1 * 8)) |
       (ELFMAG3 << (EI_MAG0 * 8)))
#endif
      )
    LOSE ("invalid ELF header");
  if (header->e_ident[EI_CLASS] != ELFCLASS32)
    LOSE ("ELF file class not 32-bit");
  if (header->e_ident[EI_DATA] != byteorder)
    LOSE ("ELF file data encoding not " byteorder_name);
  if (header->e_ident[EI_VERSION] != EV_CURRENT)
    LOSE ("ELF file version ident not " STRING(EV_CURRENT));
  if (header->e_version != EV_CURRENT)
    LOSE ("ELF file version not " STRING(EV_CURRENT));
  if (! elf_machine_matches_host (header->e_machine))
    LOSE ("ELF file machine architecture not " ELF_MACHINE_NAME);
  if (header->e_phentsize != sizeof (Elf32_Phdr))
    LOSE ("ELF file's phentsize not the expected size");

  /* Enter the new object in the list of loaded objects.  */
  l = _dl_new_object (realname, name, lt_loaded);
  l->l_opencount = 1;

  if (_dl_zerofd == -1)
    {
      _dl_zerofd = _dl_sysdep_open_zero_fill ();
      if (_dl_zerofd == -1)
	_dl_signal_error (errno, NULL, "cannot open zero fill device");
    }

  /* Extract the remaining details we need from the ELF header
     and then map in the program header table.  */
  l->l_entry = header->e_entry;
  type = header->e_type;
  l->l_phnum = header->e_phnum;
  phdr = map (header->e_phoff, l->l_phnum * sizeof (Elf32_Phdr));

  {
    /* Scan the program header table, collecting its load commands.  */
    struct loadcmd
      {
	Elf32_Addr mapstart, mapend, dataend, allocend;
	off_t mapoff;
	int prot;
      } loadcmds[l->l_phnum], *c;
    size_t nloadcmds = 0;

    l->l_ld = 0;
    l->l_phdr = 0;
    l->l_addr = 0;
    for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
      switch (ph->p_type)
	{
	  /* These entries tell us where to find things once the file's
	     segments are mapped in.  We record the addresses it says
	     verbatim, and later correct for the run-time load address.  */
	case PT_DYNAMIC:
	  l->l_ld = (void *) ph->p_vaddr;
	  break;
	case PT_PHDR:
	  l->l_phdr = (void *) ph->p_vaddr;
	  break;

	case PT_LOAD:
	  /* A load command tells us to map in part of the file.
	     We record the load commands and process them all later.  */
	  if (ph->p_align % pagesize != 0)
	    LOSE ("ELF load command alignment not page-aligned");
	  if ((ph->p_vaddr - ph->p_offset) % ph->p_align)
	    LOSE ("ELF load command address/offset not properly aligned");
	  {
	    struct loadcmd *c = &loadcmds[nloadcmds++];
	    c->mapstart = ph->p_vaddr & ~(ph->p_align - 1);
	    c->mapend = ((ph->p_vaddr + ph->p_filesz + pagesize - 1)
			 & ~(pagesize - 1));
	    c->dataend = ph->p_vaddr + ph->p_filesz;
	    c->allocend = ph->p_vaddr + ph->p_memsz;
	    c->mapoff = ph->p_offset & ~(ph->p_align - 1);
	    c->prot = 0;
	    if (ph->p_flags & PF_R)
	      c->prot |= PROT_READ;
	    if (ph->p_flags & PF_W)
	      c->prot |= PROT_WRITE;
	    if (ph->p_flags & PF_X)
	      c->prot |= PROT_EXEC;
	    break;
	  }
	}

    /* We are done reading the file's headers now.  Unmap them.  */
    munmap (file_mapping, mapping_size);

    /* Now process the load commands and map segments into memory.  */
    c = loadcmds;

    if (type == ET_DYN || type == ET_REL)
      {
	/* This is a position-independent shared object.  We can let the
	   kernel map it anywhere it likes, but we must have space for all
	   the segments in their specified positions relative to the first.
	   So we map the first segment without MAP_FIXED, but with its
	   extent increased to cover all the segments.  Then we unmap the
	   excess portion, and there is known sufficient space there to map
	   the later segments.  */
 	caddr_t mapat;
	mapat = map_segment (c->mapstart,
			     loadcmds[nloadcmds - 1].allocend - c->mapstart,
			     c->prot, 0, c->mapoff);
	l->l_addr = (Elf32_Addr) mapat - c->mapstart;

	/* Unmap the excess portion, and then jump into the normal
	   segment-mapping loop to handle the portion of the segment past
	   the end of the file mapping.  */
	munmap (mapat + c->mapend,
		loadcmds[nloadcmds - 1].allocend - c->mapend);
	goto postmap;
      }

    while (c < &loadcmds[nloadcmds])
      {
	if (c->mapend > c->mapstart)
	  /* Map the segment contents from the file.  */
	  map_segment (l->l_addr + c->mapstart, c->mapend - c->mapstart,
		       c->prot, MAP_FIXED, c->mapoff);

      postmap:
	if (c->allocend > c->dataend)
	  {
	    /* Extra zero pages should appear at the end of this segment,
	       after the data mapped from the file.   */
	    Elf32_Addr zero, zeroend, zeropage;

	    zero = l->l_addr + c->dataend;
	    zeroend = l->l_addr + c->allocend;
	    zeropage = (zero + pagesize - 1) & ~(pagesize - 1);

	    if (zeroend < zeropage)
	      /* All the extra data is in the last page of the segment.
		 We can just zero it.  */
	      zeropage = zeroend;

	    if (zeropage > zero)
	      {
		/* Zero the final part of the last page of the segment.  */
		if ((c->prot & PROT_WRITE) == 0)
		  {
		    /* Dag nab it.  */
		    if (mprotect ((caddr_t) (zero & ~(pagesize - 1)),
				  pagesize, c->prot|PROT_WRITE) < 0)
		      lose (errno, "cannot change memory protections");
		  }
		memset ((void *) zero, 0, zeropage - zero);
		if ((c->prot & PROT_WRITE) == 0)
		  mprotect ((caddr_t) (zero & ~(pagesize - 1)),
			    pagesize, c->prot);
	      }

	    if (zeroend > zeropage)
	      {
		/* Map the remaining zero pages in from the zero fill FD.  */
		caddr_t mapat;
		mapat = mmap ((caddr_t) zeropage, zeroend - zeropage, c->prot,
			      MAP_ANON|MAP_PRIVATE|MAP_FIXED,
			      _dl_zerofd, 0);
		if (mapat == (caddr_t) -1)
		  lose (errno, "cannot map zero-fill pages");
	      }
	  }

	++c;
      }
  }

  if (type == ET_EXEC)
    l->l_type = lt_executable;

  if (l->l_ld == 0)
    {
      if (type == ET_DYN)
	LOSE ("object file has no dynamic section");
    }
  else
    (Elf32_Addr) l->l_ld += l->l_addr;

  if (l->l_phdr == 0)
    l->l_phdr = (void *) ((const Elf32_Ehdr *) l->l_addr)->e_phoff;
  (Elf32_Addr) l->l_phdr += l->l_addr;

  elf_get_dynamic_info (l->l_ld, l->l_info);
  if (l->l_info[DT_HASH])
    _dl_setup_hash (l);

  return l;
}