libexec/ld.elf_so/map_object.c

   1 /*      $NetBSD: map_object.c,v 1.37 2009/01/06 04:01:46 mrg Exp $       */
   2
   3 /*
   4  * Copyright 1996 John D. Polstra.
   5  * Copyright 1996 Matt Thomas <matt@3am-software.com>
   6  * Copyright 2002 Charles M. Hannum <root@ihack.net>
   7  * All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  * 3. All advertising materials mentioning features or use of this software
  18  *    must display the following acknowledgement:
  19  *      This product includes software developed by John Polstra.
  20  * 4. The name of the author may not be used to endorse or promote products
  21  *    derived from this software without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  24  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  25  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  26  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  28  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  29  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  30  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  31  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  32  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #ifndef lint
  37 __RCSID("$NetBSD: map_object.c,v 1.37 2009/01/06 04:01:46 mrg Exp $");
  38 #endif /* not lint */
  39
  40 #include <errno.h>
  41 #include <stddef.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44 #include <unistd.h>
  45 #include <sys/stat.h>
  46 #include <sys/types.h>
  47 #include <sys/mman.h>
  48
  49 #include "rtld.h"
  50
  51 static int protflags(int);      /* Elf flags -> mmap protection */
  52
  53 /*
  54  * Map a shared object into memory.  The argument is a file descriptor,
  55  * which must be open on the object and positioned at its beginning.
  56  *
  57  * The return value is a pointer to a newly-allocated Obj_Entry structure
  58  * for the shared object.  Returns NULL on failure.
  59  */
  60 Obj_Entry *
  61 _rtld_map_object(const char *path, int fd, const struct stat *sb)
  62 {
  63         Obj_Entry       *obj;
  64         Elf_Ehdr        *ehdr;
  65         Elf_Phdr        *phdr;
  66         Elf_Phdr        *phlimit;
  67         Elf_Phdr        *segs[2];
  68         int              nsegs;
  69         caddr_t          mapbase = MAP_FAILED;
  70         size_t           mapsize = 0;
  71         int              mapflags;
  72         Elf_Off          base_offset;
  73 #ifdef MAP_ALIGNED
  74         Elf_Addr         base_alignment;
  75 #endif
  76         Elf_Addr         base_vaddr;
  77         Elf_Addr         base_vlimit;
  78         Elf_Addr         text_vlimit;
  79         int              text_flags;
  80         caddr_t          base_addr;
  81         Elf_Off          data_offset;
  82         Elf_Addr         data_vaddr;
  83         Elf_Addr         data_vlimit;
  84         int              data_flags;
  85         caddr_t          data_addr;
  86         caddr_t          gap_addr;
  87         size_t           gap_size;
  88 #ifdef RTLD_LOADER
  89         Elf_Addr         clear_vaddr;
  90         caddr_t          clear_addr;
  91         size_t           nclear;
  92 #endif
  93
  94         if (sb != NULL && sb->st_size < (off_t)sizeof (Elf_Ehdr)) {
  95                 _rtld_error("%s: unrecognized file format1", path);
  96                 return NULL;
  97         }
  98
  99         obj = _rtld_obj_new();
 100         obj->path = xstrdup(path);
 101         obj->pathlen = strlen(path);
 102         if (sb != NULL) {
 103                 obj->dev = sb->st_dev;
 104                 obj->ino = sb->st_ino;
 105         }
 106
 107         ehdr = mmap(NULL, _rtld_pagesz, PROT_READ, MAP_FILE | MAP_SHARED, fd,
 108             (off_t)0);
 109         obj->ehdr = ehdr;
 110         if (ehdr == MAP_FAILED) {
 111                 _rtld_error("%s: read error: %s", path, xstrerror(errno));
 112                 goto bad;
 113         }
 114         /* Make sure the file is valid */
 115         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 ||
 116             ehdr->e_ident[EI_CLASS] != ELFCLASS) {
 117                 _rtld_error("%s: unrecognized file format2 [%x != %x]", path, ehdr->e_ident[EI_CLASS], ELFCLASS);
 118                 goto bad;
 119         }
 120         /* Elf_e_ident includes class */
 121         if (ehdr->e_ident[EI_VERSION] != EV_CURRENT ||
 122             ehdr->e_version != EV_CURRENT ||
 123             ehdr->e_ident[EI_DATA] != ELFDEFNNAME(MACHDEP_ENDIANNESS)) {
 124                 _rtld_error("%s: unsupported file version", path);
 125                 goto bad;
 126         }
 127         if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) {
 128                 _rtld_error("%s: unsupported file type", path);
 129                 goto bad;
 130         }
 131         switch (ehdr->e_machine) {
 132                 ELFDEFNNAME(MACHDEP_ID_CASES)
 133         default:
 134                 _rtld_error("%s: unsupported machine", path);
 135                 goto bad;
 136         }
 137
 138         /*
 139          * We rely on the program header being in the first page.  This is
 140          * not strictly required by the ABI specification, but it seems to
 141          * always true in practice.  And, it simplifies things considerably.
 142          */
 143         assert(ehdr->e_phentsize == sizeof(Elf_Phdr));
 144         assert(ehdr->e_phoff + ehdr->e_phnum * sizeof(Elf_Phdr) <=
 145             _rtld_pagesz);
 146
 147         /*
 148          * Scan the program header entries, and save key information.
 149          *
 150          * We rely on there being exactly two load segments, text and data,
 151          * in that order.
 152          */
 153         phdr = (Elf_Phdr *) ((caddr_t)ehdr + ehdr->e_phoff);
 154         phlimit = phdr + ehdr->e_phnum;
 155         nsegs = 0;
 156         while (phdr < phlimit) {
 157                 switch (phdr->p_type) {
 158                 case PT_INTERP:
 159                         obj->interp = (void *)(uintptr_t)phdr->p_vaddr;
 160                         break;
 161
 162                 case PT_LOAD:
 163                         if (nsegs < 2)
 164                                 segs[nsegs] = phdr;
 165                         ++nsegs;
 166                         break;
 167
 168                 case PT_DYNAMIC:
 169                         obj->dynamic = (void *)(uintptr_t)phdr->p_vaddr;
 170                         break;
 171                 }
 172
 173                 ++phdr;
 174         }
 175         obj->entry = (void *)(uintptr_t)ehdr->e_entry;
 176         if (!obj->dynamic) {
 177                 _rtld_error("%s: not dynamically linked", path);
 178                 goto bad;
 179         }
 180         if (nsegs != 2) {
 181                 _rtld_error("%s: wrong number of segments (%d != 2)", path,
 182                     nsegs);
 183                 goto bad;
 184         }
 185
 186         /*
 187          * Map the entire address space of the object as a file
 188          * region to stake out our contiguous region and establish a
 189          * base for relocation.  We use a file mapping so that
 190          * the kernel will give us whatever alignment is appropriate
 191          * for the platform we're running on.
 192          *
 193          * We map it using the text protection, map the data segment
 194          * into the right place, then map an anon segment for the bss
 195          * and unmap the gaps left by padding to alignment.
 196          */
 197
 198 #ifdef MAP_ALIGNED
 199         base_alignment = segs[0]->p_align;
 200 #endif
 201         base_offset = round_down(segs[0]->p_offset);
 202         base_vaddr = round_down(segs[0]->p_vaddr);
 203         base_vlimit = round_up(segs[1]->p_vaddr + segs[1]->p_memsz);
 204         text_vlimit = round_up(segs[0]->p_vaddr + segs[0]->p_memsz);
 205         text_flags = protflags(segs[0]->p_flags);
 206         data_offset = round_down(segs[1]->p_offset);
 207         data_vaddr = round_down(segs[1]->p_vaddr);
 208         data_vlimit = round_up(segs[1]->p_vaddr + segs[1]->p_filesz);
 209         data_flags = protflags(segs[1]->p_flags);
 210 #ifdef RTLD_LOADER
 211         clear_vaddr = segs[1]->p_vaddr + segs[1]->p_filesz;
 212 #endif
 213
 214         obj->textsize = text_vlimit - base_vaddr;
 215         obj->vaddrbase = base_vaddr;
 216         obj->isdynamic = ehdr->e_type == ET_DYN;
 217
 218         /* Unmap header if it overlaps the first load section. */
 219         if (base_offset < _rtld_pagesz) {
 220                 munmap(ehdr, _rtld_pagesz);
 221                 obj->ehdr = MAP_FAILED;
 222         }
 223
 224         /*
 225          * Calculate log2 of the base section alignment.
 226          */
 227         mapflags = 0;
 228 #ifdef MAP_ALIGNED
 229         if (base_alignment > _rtld_pagesz) {
 230                 unsigned int log2 = 0;
 231                 for (; base_alignment > 1; base_alignment >>= 1)
 232                         log2++;
 233                 mapflags = MAP_ALIGNED(log2);
 234         }
 235 #endif
 236
 237 #ifdef RTLD_LOADER
 238         base_addr = obj->isdynamic ? NULL : (caddr_t)base_vaddr;
 239 #else
 240         base_addr = NULL;
 241 #endif
 242         mapsize = base_vlimit - base_vaddr;
 243         mapbase = mmap(base_addr, mapsize, text_flags,
 244             mapflags | MAP_FILE | MAP_PRIVATE, fd, base_offset);
 245         if (mapbase == MAP_FAILED) {
 246                 _rtld_error("mmap of entire address space failed: %s",
 247                     xstrerror(errno));
 248                 goto bad;
 249         }
 250
 251         /* Overlay the data segment onto the proper region. */
 252         data_addr = mapbase + (data_vaddr - base_vaddr);
 253         if (mmap(data_addr, data_vlimit - data_vaddr, data_flags,
 254             MAP_FILE | MAP_PRIVATE | MAP_FIXED, fd, data_offset) ==
 255             MAP_FAILED) {
 256                 _rtld_error("mmap of data failed: %s", xstrerror(errno));
 257                 goto bad;
 258         }
 259
 260         /* Overlay the bss segment onto the proper region. */
 261         if (mmap(mapbase + data_vlimit - base_vaddr, base_vlimit - data_vlimit,
 262             data_flags, MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0) ==
 263             MAP_FAILED) {
 264                 _rtld_error("mmap of bss failed: %s", xstrerror(errno));
 265                 goto bad;
 266         }
 267
 268         /* Unmap the gap between the text and data. */
 269         gap_addr = mapbase + round_up(text_vlimit - base_vaddr);
 270         gap_size = data_addr - gap_addr;
 271         if (gap_size != 0 && mprotect(gap_addr, gap_size, PROT_NONE) == -1) {
 272                 _rtld_error("mprotect of text -> data gap failed: %s",
 273                     xstrerror(errno));
 274                 goto bad;
 275         }
 276
 277 #ifdef RTLD_LOADER
 278         /* Clear any BSS in the last page of the data segment. */
 279         clear_addr = mapbase + (clear_vaddr - base_vaddr);
 280         if ((nclear = data_vlimit - clear_vaddr) > 0)
 281                 memset(clear_addr, 0, nclear);
 282
 283         /* Non-file portion of BSS mapped above. */
 284 #endif
 285
 286         obj->mapbase = mapbase;
 287         obj->mapsize = mapsize;
 288         obj->relocbase = mapbase - base_vaddr;
 289
 290         if (obj->dynamic)
 291                 obj->dynamic = (void *)(obj->relocbase + (Elf_Addr)(uintptr_t)obj->dynamic);
 292         if (obj->entry)
 293                 obj->entry = (void *)(obj->relocbase + (Elf_Addr)(uintptr_t)obj->entry);
 294         if (obj->interp)
 295                 obj->interp = (void *)(obj->relocbase + (Elf_Addr)(uintptr_t)obj->interp);
 296
 297         return obj;
 298
 299 bad:
 300         if (obj->ehdr != MAP_FAILED)
 301                 munmap(obj->ehdr, _rtld_pagesz);
 302         if (mapbase != MAP_FAILED)
 303                 munmap(mapbase, mapsize);
 304         _rtld_obj_free(obj);
 305         return NULL;
 306 }
 307
 308 void
 309 _rtld_obj_free(Obj_Entry *obj)
 310 {
 311         Objlist_Entry *elm;
 312
 313         xfree(obj->path);
 314         while (obj->needed != NULL) {
 315                 Needed_Entry *needed = obj->needed;
 316                 obj->needed = needed->next;
 317                 xfree(needed);
 318         }
 319         while ((elm = SIMPLEQ_FIRST(&obj->dldags)) != NULL) {
 320                 SIMPLEQ_REMOVE_HEAD(&obj->dldags, link);
 321                 xfree(elm);
 322         }
 323         while ((elm = SIMPLEQ_FIRST(&obj->dagmembers)) != NULL) {
 324                 SIMPLEQ_REMOVE_HEAD(&obj->dagmembers, link);
 325                 xfree(elm);
 326         }
 327         xfree(obj);
 328 }
 329
 330 Obj_Entry *
 331 _rtld_obj_new(void)
 332 {
 333         Obj_Entry *obj;
 334
 335         obj = CNEW(Obj_Entry);
 336         SIMPLEQ_INIT(&obj->dldags);
 337         SIMPLEQ_INIT(&obj->dagmembers);
 338         return obj;
 339 }
 340
 341 /*
 342  * Given a set of ELF protection flags, return the corresponding protection
 343  * flags for MMAP.
 344  */
 345 static int
 346 protflags(int elfflags)
 347 {
 348         int prot = 0;
 349
 350         if (elfflags & PF_R)
 351                 prot |= PROT_READ;
 352 #ifdef RTLD_LOADER
 353         if (elfflags & PF_W)
 354                 prot |= PROT_WRITE;
 355 #endif
 356         if (elfflags & PF_X)
 357                 prot |= PROT_EXEC;
 358         return prot;
 359 }