elf/readelflib.c

   1 /* Copyright (C) 1999-2021 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <elf-read-prop.h>
  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, unsigned int *isa_level,
  44                   char **soname, void *file_contents, size_t file_length)
  45 {
  46   int i;
  47   unsigned int j;
  48   unsigned int dynamic_addr;
  49   size_t dynamic_size;
  50   char *program_interpreter;
  51
  52   ElfW(Ehdr) *elf_header;
  53   ElfW(Phdr) *elf_pheader, *segment;
  54   ElfW(Dyn) *dynamic_segment, *dyn_entry;
  55   char *dynamic_strings;
  56
  57   elf_header = (ElfW(Ehdr) *) file_contents;
  58   *osversion = 0;
  59
  60   if (elf_header->e_ident [EI_CLASS] != ElfW (CLASS))
  61     {
  62       if (opt_verbose)
  63         {
  64           if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
  65             error (0, 0, _("%s is a 32 bit ELF file.\n"), file_name);
  66           else if (elf_header->e_ident [EI_CLASS] == ELFCLASS64)
  67             error (0, 0, _("%s is a 64 bit ELF file.\n"), file_name);
  68           else
  69             error (0, 0, _("Unknown ELFCLASS in file %s.\n"), file_name);
  70         }
  71       return 1;
  72     }
  73
  74   if (elf_header->e_type != ET_DYN)
  75     {
  76       error (0, 0, _("%s is not a shared object file (Type: %d).\n"), file_name,
  77              elf_header->e_type);
  78       return 1;
  79     }
  80
  81   /* Get information from elf program header.  */
  82   elf_pheader = (ElfW(Phdr) *) (elf_header->e_phoff + file_contents);
  83   check_ptr (elf_pheader);
  84
  85   /* The library is an elf library, now search for soname and
  86      libc5/libc6.  */
  87   *flag = FLAG_ELF;
  88
  89   /* The default ISA level is 0.  */
  90   *isa_level = 0;
  91
  92   dynamic_addr = 0;
  93   dynamic_size = 0;
  94   program_interpreter = NULL;
  95   for (i = 0, segment = elf_pheader;
  96        i < elf_header->e_phnum; i++, segment++)
  97     {
  98       check_ptr (segment);
  99
 100       switch (segment->p_type)
 101         {
 102         case PT_DYNAMIC:
 103           if (dynamic_addr)
 104             error (0, 0, _("more than one dynamic segment\n"));
 105
 106           dynamic_addr = segment->p_offset;
 107           dynamic_size = segment->p_filesz;
 108           break;
 109
 110         case PT_INTERP:
 111           program_interpreter = (char *) (file_contents + segment->p_offset);
 112           check_ptr (program_interpreter);
 113
 114           /* Check if this is enough to classify the binary.  */
 115           for (j = 0; j < sizeof (interpreters) / sizeof (interpreters [0]);
 116                ++j)
 117             if (strcmp (program_interpreter, interpreters[j].soname) == 0)
 118               {
 119                 *flag = interpreters[j].flag;
 120                 break;
 121               }
 122           break;
 123
 124         case PT_NOTE:
 125           if (!*osversion && segment->p_filesz >= 32 && segment->p_align >= 4)
 126             {
 127               ElfW(Word) *abi_note = (ElfW(Word) *) (file_contents
 128                                                      + segment->p_offset);
 129               ElfW(Addr) size = segment->p_filesz;
 130               /* NB: Some PT_NOTE segment may have alignment value of 0
 131                  or 1.  gABI specifies that PT_NOTE segments should be
 132                  aligned to 4 bytes in 32-bit objects and to 8 bytes in
 133                  64-bit objects.  As a Linux extension, we also support
 134                  4 byte alignment in 64-bit objects.  If p_align is less
 135                  than 4, we treate alignment as 4 bytes since some note
 136                  segments have 0 or 1 byte alignment.   */
 137               ElfW(Addr) align = segment->p_align;
 138               if (align < 4)
 139                 align = 4;
 140               else if (align != 4 && align != 8)
 141                 continue;
 142
 143               while (abi_note [0] != 4 || abi_note [1] != 16
 144                      || abi_note [2] != 1
 145                      || memcmp (abi_note + 3, "GNU", 4) != 0)
 146                 {
 147                   ElfW(Addr) note_size
 148                     = ELF_NOTE_NEXT_OFFSET (abi_note[0], abi_note[1],
 149                                             align);
 150
 151                   if (size - 32 < note_size || note_size == 0)
 152                     {
 153                       size = 0;
 154                       break;
 155                     }
 156                   size -= note_size;
 157                   abi_note = (void *) abi_note + note_size;
 158                 }
 159
 160               if (size == 0)
 161                 break;
 162
 163               *osversion = ((abi_note [4] << 24)
 164                             | ((abi_note [5] & 0xff) << 16)
 165                             | ((abi_note [6] & 0xff) << 8)
 166                             | (abi_note [7] & 0xff));
 167             }
 168           break;
 169
 170         case PT_GNU_PROPERTY:
 171           /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes
 172              in 32-bit objects and to 8 bytes in 64-bit objects.  Skip
 173              notes with incorrect alignment.  */
 174           if (segment->p_align == (__ELF_NATIVE_CLASS / 8))
 175             {
 176               const ElfW(Nhdr) *note = (const void *) (file_contents
 177                                                        + segment->p_offset);
 178               const ElfW(Addr) size = segment->p_filesz;
 179               const ElfW(Addr) align = segment->p_align;
 180
 181               const ElfW(Addr) start = (ElfW(Addr)) (uintptr_t) note;
 182               unsigned int last_type = 0;
 183
 184               while ((ElfW(Addr)) (uintptr_t) (note + 1) - start < size)
 185                 {
 186                   /* Find the NT_GNU_PROPERTY_TYPE_0 note.  */
 187                   if (note->n_namesz == 4
 188                       && note->n_type == NT_GNU_PROPERTY_TYPE_0
 189                       && memcmp (note + 1, "GNU", 4) == 0)
 190                     {
 191                       /* Check for invalid property.  */
 192                       if (note->n_descsz < 8
 193                           || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
 194                         goto done;
 195
 196                       /* Start and end of property array.  */
 197                       unsigned char *ptr = (unsigned char *) (note + 1) + 4;
 198                       unsigned char *ptr_end = ptr + note->n_descsz;
 199
 200                       do
 201                         {
 202                           unsigned int type = *(unsigned int *) ptr;
 203                           unsigned int datasz = *(unsigned int *) (ptr + 4);
 204
 205                           /* Property type must be in ascending order.  */
 206                           if (type < last_type)
 207                             goto done;
 208
 209                           ptr += 8;
 210                           if ((ptr + datasz) > ptr_end)
 211                             goto done;
 212
 213                           last_type = type;
 214
 215                           /* Target specific property processing.
 216                              Return value:
 217                                false: Continue processing the properties.
 218                                true : Stop processing the properties.
 219                            */
 220                           if (read_gnu_property (isa_level, type,
 221                                                  datasz, ptr))
 222                             goto done;
 223
 224                           /* Check the next property item.  */
 225                           ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
 226                         }
 227                       while ((ptr_end - ptr) >= 8);
 228
 229                       /* Only handle one NT_GNU_PROPERTY_TYPE_0.  */
 230                       goto done;
 231                     }
 232
 233                   note = ((const void *) note
 234                           + ELF_NOTE_NEXT_OFFSET (note->n_namesz,
 235                                                   note->n_descsz,
 236                                                   align));
 237                 }
 238             }
 239 done:
 240           break;
 241
 242         default:
 243           break;
 244         }
 245
 246     }
 247
 248   /* Now we can read the dynamic sections.  */
 249   if (dynamic_size == 0)
 250     return 1;
 251
 252   dynamic_segment = (ElfW(Dyn) *) (file_contents + dynamic_addr);
 253   check_ptr (dynamic_segment);
 254
 255   /* Find the string table.  */
 256   dynamic_strings = NULL;
 257   for (dyn_entry = dynamic_segment; dyn_entry->d_tag != DT_NULL;
 258        ++dyn_entry)
 259     {
 260       check_ptr (dyn_entry);
 261       if (dyn_entry->d_tag == DT_STRTAB)
 262         {
 263           /* Find the file offset of the segment containing the dynamic
 264              string table.  */
 265           ElfW(Off) loadoff = -1;
 266           for (i = 0, segment = elf_pheader;
 267                i < elf_header->e_phnum; i++, segment++)
 268             {
 269               if (segment->p_type == PT_LOAD
 270                   && dyn_entry->d_un.d_val >= segment->p_vaddr
 271                   && (dyn_entry->d_un.d_val - segment->p_vaddr
 272                       < segment->p_filesz))
 273                 {
 274                   loadoff = segment->p_vaddr - segment->p_offset;
 275                   break;
 276                 }
 277             }
 278           if (loadoff == (ElfW(Off)) -1)
 279             {
 280               /* Very strange. */
 281               loadoff = 0;
 282             }
 283
 284           dynamic_strings = (char *) (file_contents + dyn_entry->d_un.d_val
 285                                       - loadoff);
 286           check_ptr (dynamic_strings);
 287           break;
 288         }
 289     }
 290
 291   if (dynamic_strings == NULL)
 292     return 1;
 293
 294   /* Now read the DT_NEEDED and DT_SONAME entries.  */
 295   for (dyn_entry = dynamic_segment; dyn_entry->d_tag != DT_NULL;
 296        ++dyn_entry)
 297     {
 298       if (dyn_entry->d_tag == DT_NEEDED || dyn_entry->d_tag == DT_SONAME)
 299         {
 300           char *name = dynamic_strings + dyn_entry->d_un.d_val;
 301           check_ptr (name);
 302
 303           if (dyn_entry->d_tag == DT_NEEDED)
 304             {
 305
 306               if (*flag == FLAG_ELF)
 307                 {
 308                   /* Check if this is enough to classify the binary.  */
 309                   for (j = 0;
 310                        j < sizeof (known_libs) / sizeof (known_libs [0]);
 311                        ++j)
 312                     if (strcmp (name, known_libs [j].soname) == 0)
 313                       {
 314                         *flag = known_libs [j].flag;
 315                         break;
 316                       }
 317                 }
 318             }
 319
 320           else if (dyn_entry->d_tag == DT_SONAME)
 321             *soname = xstrdup (name);
 322
 323           /* Do we have everything we need?  */
 324           if (*soname && *flag != FLAG_ELF)
 325             return 0;
 326         }
 327     }
 328
 329   return 0;
 330 }