gcc/config/host-linux.c

   1 /* Linux host-specific hook definitions.
   2    Copyright (C) 2004, 2005, 2007, 2008, 2010 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 3, 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 COPYING3.  If not see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "hosthooks.h"
  24 #include "hosthooks-def.h"
  25
  26
  27 /* Linux has a feature called exec-shield-randomize that perturbs the
  28    address of non-fixed mapped segments by a (relatively) small amount.
  29    The feature is intended to make it harder to attack the system with
  30    buffer overflow attacks, since every invocation of a program will
  31    have its libraries and data segments at slightly different addresses.
  32
  33    This feature causes us problems with PCH because it makes it that
  34    much harder to acquire a stable location at which to map our PCH
  35    data file.
  36
  37    [ The feature causes other points of non-determinism within the
  38      compiler as well, so we'd *really* like to be able to have the
  39      driver disable exec-shield-randomize for the process group, but
  40      that isn't possible at present.  ]
  41
  42    We're going to try several things:
  43
  44       * Select an architecture specific address as "likely" and see
  45         if that's free.  For our 64-bit hosts, we can easily choose
  46         an address in Never Never Land.
  47
  48       * If exec-shield-randomize is disabled, then just use the
  49         address chosen by mmap in step one.
  50
  51       * If exec-shield-randomize is enabled, then temporarily allocate
  52         32M of memory as a buffer, then allocate PCH memory, then
  53         free the buffer.  The theory here is that the perturbation is
  54         no more than 16M, and so by allocating our buffer larger than
  55         that we make it considerably more likely that the address will
  56         be free when we want to load the data back.
  57 */
  58
  59 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
  60 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
  61
  62 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
  63 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
  64
  65 /* For various ports, try to guess a fixed spot in the vm space
  66    that's probably free.  */
  67 #if defined(__alpha)
  68 # define TRY_EMPTY_VM_SPACE     0x10000000000
  69 #elif defined(__ia64)
  70 # define TRY_EMPTY_VM_SPACE     0x2000000100000000
  71 #elif defined(__x86_64)
  72 # define TRY_EMPTY_VM_SPACE     0x1000000000
  73 #elif defined(__i386)
  74 # define TRY_EMPTY_VM_SPACE     0x60000000
  75 #elif defined(__powerpc__)
  76 # define TRY_EMPTY_VM_SPACE     0x60000000
  77 #elif defined(__s390x__)
  78 # define TRY_EMPTY_VM_SPACE     0x8000000000
  79 #elif defined(__s390__)
  80 # define TRY_EMPTY_VM_SPACE     0x60000000
  81 #elif defined(__sparc__) && defined(__LP64__)
  82 # define TRY_EMPTY_VM_SPACE     0x8000000000
  83 #elif defined(__sparc__)
  84 # define TRY_EMPTY_VM_SPACE     0x60000000
  85 #elif defined(__mc68000__)
  86 # define TRY_EMPTY_VM_SPACE     0x40000000
  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 virtual address
 117      randomization is on.  That is recorded in
 118      kernel.randomize_va_space.  An older implementation used
 119      kernel.exec-shield-randomize.  */
 120   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 121   if (f == NULL)
 122     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 123   randomize_on = false;
 124   if (f != NULL)
 125     {
 126       char buf[100];
 127       size_t c;
 128
 129       c = fread (buf, 1, sizeof buf - 1, f);
 130       if (c > 0)
 131         {
 132           buf[c] = '\0';
 133           randomize_on = (atoi (buf) > 0);
 134         }
 135       fclose (f);
 136     }
 137
 138   /* If it isn't, then accept the address that mmap selected as fine.  */
 139   if (!randomize_on)
 140     return addr;
 141
 142   /* Otherwise, we need to try again with buffer space.  */
 143   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 144   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 145   if (buffer != (void *) MAP_FAILED)
 146     munmap (buffer, buffer_size);
 147   if (addr == (void *) MAP_FAILED)
 148     return NULL;
 149   munmap (addr, size);
 150
 151   return addr;
 152 }
 153
 154 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 155    mapping the data at BASE, -1 if we couldn't.
 156
 157    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 158    a specific START address on either hpux or linux.  First we see
 159    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 160    races.  If it doesn't, we try an anonymous private mmap since the
 161    kernel is more likely to honor the BASE address in anonymous maps.
 162    We then copy the data to the anonymous private map.  This assumes
 163    of course that we don't need to change the data in the PCH file
 164    after it is created.
 165
 166    This approach obviously causes a performance penalty but there is
 167    little else we can do given the current PCH implementation.  */
 168
 169 static int
 170 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 171 {
 172   void *addr;
 173
 174   /* We're called with size == 0 if we're not planning to load a PCH
 175      file at all.  This allows the hook to free any static space that
 176      we might have allocated at link time.  */
 177   if (size == 0)
 178     return -1;
 179
 180   /* Try to map the file with MAP_PRIVATE.  */
 181   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 182
 183   if (addr == base)
 184     return 1;
 185
 186   if (addr != (void *) MAP_FAILED)
 187     munmap (addr, size);
 188
 189   /* Try to make an anonymous private mmap at the desired location.  */
 190   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 191                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 192
 193   if (addr != base)
 194     {
 195       if (addr != (void *) MAP_FAILED)
 196         munmap (addr, size);
 197       return -1;
 198     }
 199
 200   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 201     return -1;
 202
 203   while (size)
 204     {
 205       ssize_t nbytes;
 206
 207       nbytes = read (fd, base, MIN (size, SSIZE_MAX));
 208       if (nbytes <= 0)
 209         return -1;
 210       base = (char *) base + nbytes;
 211       size -= nbytes;
 212     }
 213
 214   return 1;
 215 }
 216
 217 \f
 218 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;