elf/readelflib.c

   1 /* Copyright (C) 1999-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Andreas Jaeger <aj@suse.de>, 1999 and
   4                   Jakub Jelinek <jakub@redhat.com>, 1999.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 /* This code is a heavily simplified version of the readelf program
  21    that's part of the current binutils development version.  For architectures
  22    which need to handle both 32bit and 64bit ELF libraries,  this file is
  23    included twice for each arch size.  */
  24
  25 /* check_ptr checks that a pointer is in the mmaped file and doesn't
  26    point outside it.  */
  27 #undef check_ptr
  28 #define check_ptr(ptr)                                          \
  29 do                                                              \
  30   {                                                             \
  31     if ((void *)(ptr) < file_contents                           \
  32         || (void *)(ptr) > (file_contents+file_length))         \
  33       {                                                         \
  34         error (0, 0, _("file %s is truncated\n"), file_name);   \
  35         return 1;                                               \
  36       }                                                         \
  37   }                                                             \
  38  while (0);
  39
  40 /* Returns 0 if everything is ok, != 0 in case of error.  */
  41 int
  42 process_elf_file (const char *file_name, const char *lib, int *flag,
  43                   unsigned int *osversion, char **soname, void *file_contents,
  44                   size_t file_length)
  45 {
  46   int i;
  47   unsigned int j;
  48   ElfW(Addr) loadaddr;
  49   unsigned int dynamic_addr;
  50   size_t dynamic_size;
  51   char *program_interpreter;
  52
  53   ElfW(Ehdr) *elf_header;
  54   ElfW(Phdr) *elf_pheader, *segment;
  55   ElfW(Dyn) *dynamic_segment, *dyn_entry;
  56   char *dynamic_strings;
  57
  58   elf_header = (ElfW(Ehdr) *) file_contents;
  59   *osversion = 0;
  60
  61   if (elf_header->e_ident [EI_CLASS] != ElfW (CLASS))
  62     {
  63       if (opt_verbose)
  64         {
  65           if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
  66             error (0, 0, _("%s is a 32 bit ELF file.\n"), file_name);
  67           else if (elf_header->e_ident [EI_CLASS] == ELFCLASS64)
  68             error (0, 0, _("%s is a 64 bit ELF file.\n"), file_name);
  69           else
  70             error (0, 0, _("Unknown ELFCLASS in file %s.\n"), file_name);
  71         }
  72       return 1;
  73     }
  74
  75   if (elf_header->e_type != ET_DYN)
  76     {
  77       error (0, 0, _("%s is not a shared object file (Type: %d).\n"), file_name,
  78              elf_header->e_type);
  79       return 1;
  80     }
  81
  82   /* Get information from elf program header.  */
  83   elf_pheader = (ElfW(Phdr) *) (elf_header->e_phoff + file_contents);
  84   check_ptr (elf_pheader);
  85
  86   /* The library is an elf library, now search for soname and
  87      libc5/libc6.  */
  88   *flag = FLAG_ELF;
  89
  90   loadaddr = -1;
  91   dynamic_addr = 0;
  92   dynamic_size = 0;
  93   program_interpreter = NULL;
  94   for (i = 0, segment = elf_pheader;
  95        i < elf_header->e_phnum; i++, segment++)
  96     {
  97       check_ptr (segment);
  98
  99       switch (segment->p_type)
 100         {
 101         case PT_LOAD:
 102           if (loadaddr == (ElfW(Addr)) -1)
 103             loadaddr = segment->p_vaddr - segment->p_offset;
 104           break;
 105
 106         case PT_DYNAMIC:
 107           if (dynamic_addr)
 108             error (0, 0, _("more than one dynamic segment\n"));
 109
 110           dynamic_addr = segment->p_offset;
 111           dynamic_size = segment->p_filesz;
 112           break;
 113
 114         case PT_INTERP:
 115           program_interpreter = (char *) (file_contents + segment->p_offset);
 116           check_ptr (program_interpreter);
 117
 118           /* Check if this is enough to classify the binary.  */
 119           for (j = 0; j < sizeof (interpreters) / sizeof (interpreters [0]);
 120                ++j)
 121             if (strcmp (program_interpreter, interpreters[j].soname) == 0)
 122               {
 123                 *flag = interpreters[j].flag;
 124                 break;
 125               }
 126           break;
 127
 128         case PT_NOTE:
 129           if (!*osversion && segment->p_filesz >= 32 && segment->p_align >= 4)
 130             {
 131               ElfW(Word) *abi_note = (ElfW(Word) *) (file_contents
 132                                                      + segment->p_offset);
 133               ElfW(Addr) size = segment->p_filesz;
 134
 135               while (abi_note [0] != 4 || abi_note [1] != 16
 136                      || abi_note [2] != 1
 137                      || memcmp (abi_note + 3, "GNU", 4) != 0)
 138                 {
 139 #define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
 140                   ElfW(Addr) note_size = 3 * sizeof (ElfW(Word))
 141                                          + ROUND (abi_note[0])
 142                                          + ROUND (abi_note[1]);
 143
 144                   if (size - 32 < note_size || note_size == 0)
 145                     {
 146                       size = 0;
 147                       break;
 148                     }
 149                   size -= note_size;
 150                   abi_note = (void *) abi_note + note_size;
 151                 }
 152
 153               if (size == 0)
 154                 break;
 155
 156               *osversion = (abi_note [4] << 24) |
 157                            ((abi_note [5] & 0xff) << 16) |
 158                            ((abi_note [6] & 0xff) << 8) |
 159                            (abi_note [7] & 0xff);
 160             }
 161           break;
 162
 163         default:
 164           break;
 165         }
 166
 167     }
 168   if (loadaddr == (ElfW(Addr)) -1)
 169     {
 170       /* Very strange. */
 171       loadaddr = 0;
 172     }
 173
 174   /* Now we can read the dynamic sections.  */
 175   if (dynamic_size == 0)
 176     return 1;
 177
 178   dynamic_segment = (ElfW(Dyn) *) (file_contents + dynamic_addr);
 179   check_ptr (dynamic_segment);
 180
 181   /* Find the string table.  */
 182   dynamic_strings = NULL;
 183   for (dyn_entry = dynamic_segment; dyn_entry->d_tag != DT_NULL;
 184        ++dyn_entry)
 185     {
 186       check_ptr (dyn_entry);
 187       if (dyn_entry->d_tag == DT_STRTAB)
 188         {
 189           dynamic_strings = (char *) (file_contents + dyn_entry->d_un.d_val - loadaddr);
 190           check_ptr (dynamic_strings);
 191           break;
 192         }
 193     }
 194
 195   if (dynamic_strings == NULL)
 196     return 1;
 197
 198   /* Now read the DT_NEEDED and DT_SONAME entries.  */
 199   for (dyn_entry = dynamic_segment; dyn_entry->d_tag != DT_NULL;
 200        ++dyn_entry)
 201     {
 202       if (dyn_entry->d_tag == DT_NEEDED || dyn_entry->d_tag == DT_SONAME)
 203         {
 204           char *name = dynamic_strings + dyn_entry->d_un.d_val;
 205           check_ptr (name);
 206
 207           if (dyn_entry->d_tag == DT_NEEDED)
 208             {
 209
 210               if (*flag == FLAG_ELF)
 211                 {
 212                   /* Check if this is enough to classify the binary.  */
 213                   for (j = 0;
 214                        j < sizeof (known_libs) / sizeof (known_libs [0]);
 215                        ++j)
 216                     if (strcmp (name, known_libs [j].soname) == 0)
 217                       {
 218                         *flag = known_libs [j].flag;
 219                         break;
 220                       }
 221                 }
 222             }
 223
 224           else if (dyn_entry->d_tag == DT_SONAME)
 225             *soname = xstrdup (name);
 226
 227           /* Do we have everything we need?  */
 228           if (*soname && *flag != FLAG_ELF)
 229             return 0;
 230         }
 231     }
 232
 233   return 0;
 234 }