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, 51 Franklin Street, Fifth Floor, Boston,
  19    MA 02110-1301, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include <sys/mman.h>
  25 #include <limits.h>
  26 #include "hosthooks.h"
  27 #include "hosthooks-def.h"
  28
  29
  30 /* Linux has a feature called exec-shield-randomize that perturbs the
  31    address of non-fixed mapped segments by a (relatively) small amount.
  32    The feature is intended to make it harder to attack the system with
  33    buffer overflow attacks, since every invocation of a program will
  34    have its libraries and data segments at slightly different addresses.
  35
  36    This feature causes us problems with PCH because it makes it that
  37    much harder to acquire a stable location at which to map our PCH
  38    data file.
  39
  40    [ The feature causes other points of non-determinism within the
  41      compiler as well, so we'd *really* like to be able to have the
  42      driver disable exec-shield-randomize for the process group, but
  43      that isn't possible at present.  ]
  44
  45    We're going to try several things:
  46
  47       * Select an architecture specific address as "likely" and see
  48         if that's free.  For our 64-bit hosts, we can easily choose
  49         an address in Never Never Land.
  50
  51       * If exec-shield-randomize is disabled, then just use the
  52         address chosen by mmap in step one.
  53
  54       * If exec-shield-randomize is enabled, then temporarily allocate
  55         32M of memory as a buffer, then allocate PCH memory, then
  56         free the buffer.  The theory here is that the perturbation is
  57         no more than 16M, and so by allocating our buffer larger than
  58         that we make it considerably more likely that the address will
  59         be free when we want to load the data back.
  60 */
  61
  62 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
  63 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
  64
  65 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
  66 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
  67
  68 /* For various ports, try to guess a fixed spot in the vm space
  69    that's probably free.  */
  70 #if defined(__alpha)
  71 # define TRY_EMPTY_VM_SPACE     0x10000000000
  72 #elif defined(__ia64)
  73 # define TRY_EMPTY_VM_SPACE     0x2000000100000000
  74 #elif defined(__x86_64)
  75 # define TRY_EMPTY_VM_SPACE     0x1000000000
  76 #elif defined(__i386)
  77 # define TRY_EMPTY_VM_SPACE     0x60000000
  78 #elif defined(__powerpc__)
  79 # define TRY_EMPTY_VM_SPACE     0x60000000
  80 #elif defined(__s390x__)
  81 # define TRY_EMPTY_VM_SPACE     0x8000000000
  82 #elif defined(__s390__)
  83 # define TRY_EMPTY_VM_SPACE     0x60000000
  84 #elif defined(__sparc__) && defined(__LP64__)
  85 # define TRY_EMPTY_VM_SPACE     0x8000000000
  86 #elif defined(__sparc__)
  87 # define TRY_EMPTY_VM_SPACE     0x60000000
  88 #else
  89 # define TRY_EMPTY_VM_SPACE     0
  90 #endif
  91
  92 /* Determine a location where we might be able to reliably allocate SIZE
  93    bytes.  FD is the PCH file, though we should return with the file
  94    unmapped.  */
  95
  96 static void *
  97 linux_gt_pch_get_address (size_t size, int fd)
  98 {
  99   size_t buffer_size = 32 * 1024 * 1024;
 100   void *addr, *buffer;
 101   FILE *f;
 102   bool randomize_on;
 103
 104   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 105                MAP_PRIVATE, fd, 0);
 106
 107   /* If we failed the map, that means there's *no* free space.  */
 108   if (addr == (void *) MAP_FAILED)
 109     return NULL;
 110   /* Unmap the area before returning.  */
 111   munmap (addr, size);
 112
 113   /* If we got the exact area we requested, then that's great.  */
 114   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 115     return addr;
 116
 117   /* If we didn't, then we need to look to see if virtual address
 118      randomization is on.  That is recorded in
 119      kernel.randomize_va_space.  An older implementation used
 120      kernel.exec-shield-randomize.  */
 121   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 122   if (f == NULL)
 123     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 124   randomize_on = false;
 125   if (f != NULL)
 126     {
 127       char buf[100];
 128       size_t c;
 129
 130       c = fread (buf, 1, sizeof buf - 1, f);
 131       if (c > 0)
 132         {
 133           buf[c] = '\0';
 134           randomize_on = (atoi (buf) > 0);
 135         }
 136       fclose (f);
 137     }
 138
 139   /* If it isn't, then accept the address that mmap selected as fine.  */
 140   if (!randomize_on)
 141     return addr;
 142
 143   /* Otherwise, we need to try again with buffer space.  */
 144   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 145   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 146   if (buffer != (void *) MAP_FAILED)
 147     munmap (buffer, buffer_size);
 148   if (addr == (void *) MAP_FAILED)
 149     return NULL;
 150   munmap (addr, size);
 151
 152   return addr;
 153 }
 154
 155 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 156    mapping the data at BASE, -1 if we couldn't.
 157
 158    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 159    a specific START address on either hpux or linux.  First we see
 160    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 161    races.  If it doesn't, we try an anonymous private mmap since the
 162    kernel is more likely to honor the BASE address in anonymous maps.
 163    We then copy the data to the anonymous private map.  This assumes
 164    of course that we don't need to change the data in the PCH file
 165    after it is created.
 166
 167    This approach obviously causes a performance penalty but there is
 168    little else we can do given the current PCH implementation.  */
 169
 170 static int
 171 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 172 {
 173   void *addr;
 174
 175   /* We're called with size == 0 if we're not planning to load a PCH
 176      file at all.  This allows the hook to free any static space that
 177      we might have allocated at link time.  */
 178   if (size == 0)
 179     return -1;
 180
 181   /* Try to map the file with MAP_PRIVATE.  */
 182   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 183
 184   if (addr == base)
 185     return 1;
 186
 187   if (addr != (void *) MAP_FAILED)
 188     munmap (addr, size);
 189
 190   /* Try to make an anonymous private mmap at the desired location.  */
 191   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 192                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 193
 194   if (addr != base)
 195     {
 196       if (addr != (void *) MAP_FAILED)
 197         munmap (addr, size);
 198       return -1;
 199     }
 200
 201   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 202     return -1;
 203
 204   while (size)
 205     {
 206       ssize_t nbytes;
 207
 208       nbytes = read (fd, base, MIN (size, SSIZE_MAX));
 209       if (nbytes <= 0)
 210         return -1;
 211       base = (char *) base + nbytes;
 212       size -= nbytes;
 213     }
 214
 215   return 1;
 216 }
 217
 218 \f
 219 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;