gcc/config/host-linux.c

   1 /* Linux host-specific hook definitions.
   2    Copyright (C) 2004, 2005 Free Software Foundation, Inc.
   3
   4    This file is part of GCC.
   5
   6    GCC is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published
   8    by the Free Software Foundation; either version 2, or (at your
   9    option) any later version.
  10
  11    GCC is distributed in the hope that it will be useful, but WITHOUT
  12    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  13    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  14    License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with GCC; see the file COPYING.  If not, write to the
  18    Free Software Foundation, 59 Temple Place - Suite 330, Boston,
  19    MA 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include <sys/mman.h>
  25 #include "hosthooks.h"
  26 #include "hosthooks-def.h"
  27
  28
  29 /* Linux has a feature called exec-shield-randomize that perturbs the
  30    address of non-fixed mapped segments by a (relatively) small amount.
  31    The feature is intended to make it harder to attack the system with
  32    buffer overflow attacks, since every invocation of a program will
  33    have its libraries and data segments at slightly different addresses.
  34
  35    This feature causes us problems with PCH because it makes it that
  36    much harder to acquire a stable location at which to map our PCH
  37    data file.
  38
  39    [ The feature causes other points of non-determinism within the
  40      compiler as well, so we'd *really* like to be able to have the
  41      driver disable exec-shield-randomize for the process group, but
  42      that isn't possible at present.  ]
  43
  44    We're going to try several things:
  45
  46       * Select an architecture specific address as "likely" and see
  47         if that's free.  For our 64-bit hosts, we can easily choose
  48         an address in Never Never Land.
  49
  50       * If exec-shield-randomize is disabled, then just use the
  51         address chosen by mmap in step one.
  52
  53       * If exec-shield-randomize is enabled, then temporarily allocate
  54         32M of memory as a buffer, then allocate PCH memory, then
  55         free the buffer.  The theory here is that the perturbation is
  56         no more than 16M, and so by allocating our buffer larger than
  57         that we make it considerably more likely that the address will
  58         be free when we want to load the data back.
  59 */
  60
  61 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
  62 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
  63
  64 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
  65 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
  66
  67 /* For various ports, try to guess a fixed spot in the vm space
  68    that's probably free.  */
  69 #if defined(__alpha)
  70 # define TRY_EMPTY_VM_SPACE     0x10000000000
  71 #elif defined(__ia64)
  72 # define TRY_EMPTY_VM_SPACE     0x2000000100000000
  73 #elif defined(__x86_64)
  74 # define TRY_EMPTY_VM_SPACE     0x1000000000
  75 #elif defined(__i386)
  76 # define TRY_EMPTY_VM_SPACE     0x60000000
  77 #elif defined(__powerpc__)
  78 # define TRY_EMPTY_VM_SPACE     0x60000000
  79 #elif defined(__s390x__)
  80 # define TRY_EMPTY_VM_SPACE     0x8000000000
  81 #elif defined(__s390__)
  82 # define TRY_EMPTY_VM_SPACE     0x60000000
  83 #elif defined(__sparc__) && defined(__LP64__)
  84 # define TRY_EMPTY_VM_SPACE     0x8000000000
  85 #elif defined(__sparc__)
  86 # define TRY_EMPTY_VM_SPACE     0x60000000
  87 #else
  88 # define TRY_EMPTY_VM_SPACE     0
  89 #endif
  90
  91 /* Determine a location where we might be able to reliably allocate SIZE
  92    bytes.  FD is the PCH file, though we should return with the file
  93    unmapped.  */
  94
  95 static void *
  96 linux_gt_pch_get_address (size_t size, int fd)
  97 {
  98   size_t buffer_size = 32 * 1024 * 1024;
  99   void *addr, *buffer;
 100   FILE *f;
 101   bool randomize_on;
 102
 103   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 104                MAP_PRIVATE, fd, 0);
 105
 106   /* If we failed the map, that means there's *no* free space.  */
 107   if (addr == (void *) MAP_FAILED)
 108     return NULL;
 109   /* Unmap the area before returning.  */
 110   munmap (addr, size);
 111
 112   /* If we got the exact area we requested, then that's great.  */
 113   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 114     return addr;
 115
 116   /* If we didn't, then we need to look to see if randomization is on.  */
 117   f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 118   randomize_on = false;
 119   if (f != NULL)
 120     {
 121       char buf[100];
 122       size_t c;
 123
 124       c = fread (buf, 1, sizeof buf - 1, f);
 125       if (c > 0)
 126         {
 127           buf[c] = '\0';
 128           randomize_on = (atoi (buf) > 0);
 129         }
 130       fclose (f);
 131     }
 132
 133   /* If it isn't, then accept the address that mmap selected as fine.  */
 134   if (!randomize_on)
 135     return addr;
 136
 137   /* Otherwise, we need to try again with buffer space.  */
 138   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 139   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 140   if (buffer != (void *) MAP_FAILED)
 141     munmap (buffer, buffer_size);
 142   if (addr == (void *) MAP_FAILED)
 143     return NULL;
 144   munmap (addr, size);
 145
 146   return addr;
 147 }
 148
 149 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 150    mapping the data at BASE, -1 if we couldn't.
 151
 152    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 153    a specific START address on either hpux or linux.  First we see
 154    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 155    races.  If it doesn't, we try an anonymous private mmap since the
 156    kernel is more likely to honor the BASE address in anonymous maps.
 157    We then copy the data to the anonymous private map.  This assumes
 158    of course that we don't need to change the data in the PCH file
 159    after it is created.
 160
 161    This approach obviously causes a performance penalty but there is
 162    little else we can do given the current PCH implementation.  */
 163
 164 static int
 165 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 166 {
 167   void *addr;
 168
 169   /* We're called with size == 0 if we're not planning to load a PCH
 170      file at all.  This allows the hook to free any static space that
 171      we might have allocated at link time.  */
 172   if (size == 0)
 173     return -1;
 174
 175   /* Try to map the file with MAP_PRIVATE.  */
 176   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 177
 178   if (addr == base)
 179     return 1;
 180
 181   if (addr != (void *) MAP_FAILED)
 182     munmap (addr, size);
 183
 184   /* Try to make an anonymous private mmap at the desired location.  */
 185   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 186                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 187
 188   if (addr != base)
 189     {
 190       if (addr != (void *) MAP_FAILED)
 191         munmap (addr, size);
 192       return -1;
 193     }
 194
 195   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 196     return -1;
 197
 198   while (size)
 199     {
 200       ssize_t nbytes;
 201
 202       nbytes = read (fd, base, MIN (size, SSIZE_MAX));
 203       if (nbytes <= 0)
 204         return -1;
 205       base = (char *) base + nbytes;
 206       size -= nbytes;
 207     }
 208
 209   return 1;
 210 }
 211
 212 \f
 213 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;