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) && defined(__LP64__)
  72 # define TRY_EMPTY_VM_SPACE     0x1000000000
  73 #elif defined(__x86_64)
  74 # define TRY_EMPTY_VM_SPACE     0x60000000
  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 #elif defined(__mc68000__)
  88 # define TRY_EMPTY_VM_SPACE     0x40000000
  89 #elif defined(__ARM_EABI__)
  90 # define TRY_EMPTY_VM_SPACE     0x60000000
  91 #elif defined(__mips__) && defined(__LP64__)
  92 # define TRY_EMPTY_VM_SPACE     0x8000000000
  93 #elif defined(__mips__)
  94 # define TRY_EMPTY_VM_SPACE     0x60000000
  95 #else
  96 # define TRY_EMPTY_VM_SPACE     0
  97 #endif
  98
  99 /* Determine a location where we might be able to reliably allocate SIZE
 100    bytes.  FD is the PCH file, though we should return with the file
 101    unmapped.  */
 102
 103 static void *
 104 linux_gt_pch_get_address (size_t size, int fd)
 105 {
 106   size_t buffer_size = 32 * 1024 * 1024;
 107   void *addr, *buffer;
 108   FILE *f;
 109   bool randomize_on;
 110
 111   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 112                MAP_PRIVATE, fd, 0);
 113
 114   /* If we failed the map, that means there's *no* free space.  */
 115   if (addr == (void *) MAP_FAILED)
 116     return NULL;
 117   /* Unmap the area before returning.  */
 118   munmap (addr, size);
 119
 120   /* If we got the exact area we requested, then that's great.  */
 121   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 122     return addr;
 123
 124   /* If we didn't, then we need to look to see if virtual address
 125      randomization is on.  That is recorded in
 126      kernel.randomize_va_space.  An older implementation used
 127      kernel.exec-shield-randomize.  */
 128   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 129   if (f == NULL)
 130     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 131   randomize_on = false;
 132   if (f != NULL)
 133     {
 134       char buf[100];
 135       size_t c;
 136
 137       c = fread (buf, 1, sizeof buf - 1, f);
 138       if (c > 0)
 139         {
 140           buf[c] = '\0';
 141           randomize_on = (atoi (buf) > 0);
 142         }
 143       fclose (f);
 144     }
 145
 146   /* If it isn't, then accept the address that mmap selected as fine.  */
 147   if (!randomize_on)
 148     return addr;
 149
 150   /* Otherwise, we need to try again with buffer space.  */
 151   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 152   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 153   if (buffer != (void *) MAP_FAILED)
 154     munmap (buffer, buffer_size);
 155   if (addr == (void *) MAP_FAILED)
 156     return NULL;
 157   munmap (addr, size);
 158
 159   return addr;
 160 }
 161
 162 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 163    mapping the data at BASE, -1 if we couldn't.
 164
 165    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 166    a specific START address on either hpux or linux.  First we see
 167    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 168    races.  If it doesn't, we try an anonymous private mmap since the
 169    kernel is more likely to honor the BASE address in anonymous maps.
 170    We then copy the data to the anonymous private map.  This assumes
 171    of course that we don't need to change the data in the PCH file
 172    after it is created.
 173
 174    This approach obviously causes a performance penalty but there is
 175    little else we can do given the current PCH implementation.  */
 176
 177 static int
 178 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 179 {
 180   void *addr;
 181
 182   /* We're called with size == 0 if we're not planning to load a PCH
 183      file at all.  This allows the hook to free any static space that
 184      we might have allocated at link time.  */
 185   if (size == 0)
 186     return -1;
 187
 188   /* Try to map the file with MAP_PRIVATE.  */
 189   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 190
 191   if (addr == base)
 192     return 1;
 193
 194   if (addr != (void *) MAP_FAILED)
 195     munmap (addr, size);
 196
 197   /* Try to make an anonymous private mmap at the desired location.  */
 198   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 199                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 200
 201   if (addr != base)
 202     {
 203       if (addr != (void *) MAP_FAILED)
 204         munmap (addr, size);
 205       return -1;
 206     }
 207
 208   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 209     return -1;
 210
 211   while (size)
 212     {
 213       ssize_t nbytes;
 214
 215       nbytes = read (fd, base, MIN (size, SSIZE_MAX));
 216       if (nbytes <= 0)
 217         return -1;
 218       base = (char *) base + nbytes;
 219       size -= nbytes;
 220     }
 221
 222   return 1;
 223 }
 224
 225 \f
 226 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;