elf/check-textrel.c

   1 /* Check for text relocations in DSOs.
   2    Copyright (C) 2002, 2003, 2006 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contribute by Ulrich Drepper <drepper@redhat.com>. 2002.
   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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <byteswap.h>
  22 #include <elf.h>
  23 #include <endian.h>
  24 #include <fcntl.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29
  30
  31 #ifdef BITS
  32
  33 # define AB(name) _AB (name, BITS)
  34 # define _AB(name, bits) __AB (name, bits)
  35 # define __AB(name, bits) name##bits
  36 # define E(name) _E (name, BITS)
  37 # define _E(name, bits) __E (name, bits)
  38 # define __E(name, bits) Elf##bits##_##name
  39 # define SWAP(val) \
  40   ({ __typeof (val) __res;                                                    \
  41      if (((ehdr.e_ident[EI_DATA] == ELFDATA2MSB                               \
  42            && BYTE_ORDER == LITTLE_ENDIAN)                                    \
  43           || (ehdr.e_ident[EI_DATA] == ELFDATA2LSB                            \
  44               && BYTE_ORDER == BIG_ENDIAN))                                   \
  45          && sizeof (val) != 1)                                                \
  46        {                                                                      \
  47          if (sizeof (val) == 2)                                               \
  48            __res = bswap_16 (val);                                            \
  49          else if (sizeof (val) == 4)                                          \
  50            __res = bswap_32 (val);                                            \
  51          else                                                                 \
  52            __res = bswap_64 (val);                                            \
  53        }                                                                      \
  54      else                                                                     \
  55        __res = (val);                                                         \
  56      __res; })
  57
  58
  59 static int
  60 AB(handle_file) (const char *fname, int fd)
  61 {
  62   E(Ehdr) ehdr;
  63
  64   if (pread (fd, &ehdr, sizeof (ehdr), 0) != sizeof (ehdr))
  65     {
  66     read_error:
  67       printf ("%s: read error: %m\n", fname);
  68       return 1;
  69     }
  70
  71   const size_t phnum = SWAP (ehdr.e_phnum);
  72   const size_t phentsize = SWAP (ehdr.e_phentsize);
  73
  74   /* Read the program header.  */
  75   E(Phdr) *phdr = alloca (phentsize * phnum);
  76   if (pread (fd, phdr, phentsize * phnum, SWAP (ehdr.e_phoff))
  77       != phentsize * phnum)
  78     goto read_error;
  79
  80   /* Search for the PT_DYNAMIC entry.  */
  81   size_t cnt;
  82   E(Phdr) *dynphdr = NULL;
  83   for (cnt = 0; cnt < phnum; ++cnt)
  84     if (SWAP (phdr[cnt].p_type) == PT_DYNAMIC)
  85       dynphdr = &phdr[cnt];
  86     else if (SWAP (phdr[cnt].p_type) == PT_LOAD
  87              && (SWAP (phdr[cnt].p_flags) & (PF_X | PF_W)) == (PF_X | PF_W))
  88       {
  89         printf ("%s: segment %zu is executable and writable\n",
  90                 fname, cnt);
  91 #if !defined __sparc__ \
  92     && !defined __alpha__ \
  93     && (!defined __powerpc__ || defined __powerpc64__ || defined HAVE_PPC_SECURE_PLT)
  94         /* sparc, sparc64, alpha and powerpc32 (the last one only when using
  95            -mbss-plt) are expected to have PF_X | PF_W segment containing .plt
  96            section, it is part of their ABI.  It is bad security wise, nevertheless
  97            this test shouldn't fail because of this.  */
  98         return 1;
  99 #endif
 100       }
 101
 102   if (dynphdr == NULL)
 103     {
 104       printf ("%s: no DYNAMIC segment found\n", fname);
 105       return 1;
 106     }
 107
 108   /* Read the dynamic segment.  */
 109   size_t pmemsz = SWAP(dynphdr->p_memsz);
 110   E(Dyn) *dyn = alloca (pmemsz);
 111   if (pread (fd, dyn, pmemsz, SWAP(dynphdr->p_offset)) != pmemsz)
 112     goto read_error;
 113
 114   /* Search for an DT_TEXTREL entry of DT_FLAGS with the DF_TEXTREL
 115      bit set.  */
 116   for (cnt = 0; (cnt + 1) * sizeof (E(Dyn)) - 1 < pmemsz; ++cnt)
 117     {
 118       unsigned int tag = SWAP (dyn[cnt].d_tag);
 119
 120       if (tag == DT_NULL)
 121         /* We reached the end.  */
 122         break;
 123
 124       if (tag == DT_TEXTREL
 125           || (tag == DT_FLAGS
 126               && (SWAP (dyn[cnt].d_un.d_val) & DF_TEXTREL) != 0))
 127         {
 128           /* Urgh!  The DSO has text relocations.  */
 129           printf ("%s: text relocations used\n", fname);
 130           return 1;
 131         }
 132     }
 133
 134   printf ("%s: OK\n", fname);
 135
 136   return 0;
 137 }
 138
 139 # undef BITS
 140 #else
 141
 142 # define BITS 32
 143 # include "check-textrel.c"
 144
 145 # define BITS 64
 146 # include "check-textrel.c"
 147
 148
 149 static int
 150 handle_file (const char *fname)
 151 {
 152   int fd = open (fname, O_RDONLY);
 153   if (fd == -1)
 154     {
 155       printf ("cannot open %s: %m\n", fname);
 156       return 1;
 157     }
 158
 159   /* Read was is supposed to be the ELF header.  Read the initial
 160      bytes to determine whether this is a 32 or 64 bit file.  */
 161   char ident[EI_NIDENT];
 162   if (read (fd, ident, EI_NIDENT) != EI_NIDENT)
 163     {
 164       printf ("%s: read error: %m\n", fname);
 165       close (fd);
 166       return 1;
 167     }
 168
 169   if (memcmp (&ident[EI_MAG0], ELFMAG, SELFMAG) != 0)
 170     {
 171       printf ("%s: not an ELF file\n", fname);
 172       close (fd);
 173       return 1;
 174     }
 175
 176   int result;
 177   if (ident[EI_CLASS] == ELFCLASS64)
 178     result = handle_file64 (fname, fd);
 179   else
 180     result = handle_file32 (fname, fd);
 181
 182   close (fd);
 183
 184   return result;
 185 }
 186
 187
 188 int
 189 main (int argc, char *argv[])
 190 {
 191   int cnt;
 192   int result = 0;
 193
 194   for (cnt = 1; cnt < argc; ++cnt)
 195     result |= handle_file (argv[cnt]);
 196
 197   return result;
 198 }
 199 #endif