gcc/config/host-linux.c

   1 /* Linux host-specific hook definitions.
   2    Copyright (C) 2004-2021 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(__aarch64__) && defined(__ILP32__)
  90 # define TRY_EMPTY_VM_SPACE     0x60000000
  91 #elif defined(__aarch64__)
  92 # define TRY_EMPTY_VM_SPACE     0x1000000000
  93 #elif defined(__ARM_EABI__)
  94 # define TRY_EMPTY_VM_SPACE     0x60000000
  95 #elif defined(__mips__) && defined(__LP64__)
  96 # define TRY_EMPTY_VM_SPACE     0x8000000000
  97 #elif defined(__mips__)
  98 # define TRY_EMPTY_VM_SPACE     0x60000000
  99 #elif defined(__riscv) && defined (__LP64__)
 100 # define TRY_EMPTY_VM_SPACE     0x1000000000
 101 #else
 102 # define TRY_EMPTY_VM_SPACE     0
 103 #endif
 104
 105 /* Determine a location where we might be able to reliably allocate SIZE
 106    bytes.  FD is the PCH file, though we should return with the file
 107    unmapped.  */
 108
 109 static void *
 110 linux_gt_pch_get_address (size_t size, int fd)
 111 {
 112   size_t buffer_size = 32 * 1024 * 1024;
 113   void *addr, *buffer;
 114   FILE *f;
 115   bool randomize_on;
 116
 117   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 118                MAP_PRIVATE, fd, 0);
 119
 120   /* If we failed the map, that means there's *no* free space.  */
 121   if (addr == (void *) MAP_FAILED)
 122     return NULL;
 123   /* Unmap the area before returning.  */
 124   munmap (addr, size);
 125
 126   /* If we got the exact area we requested, then that's great.  */
 127   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 128     return addr;
 129
 130   /* If we didn't, then we need to look to see if virtual address
 131      randomization is on.  That is recorded in
 132      kernel.randomize_va_space.  An older implementation used
 133      kernel.exec-shield-randomize.  */
 134   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 135   if (f == NULL)
 136     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 137   randomize_on = false;
 138   if (f != NULL)
 139     {
 140       char buf[100];
 141       size_t c;
 142
 143       c = fread (buf, 1, sizeof buf - 1, f);
 144       if (c > 0)
 145         {
 146           buf[c] = '\0';
 147           randomize_on = (atoi (buf) > 0);
 148         }
 149       fclose (f);
 150     }
 151
 152   /* If it isn't, then accept the address that mmap selected as fine.  */
 153   if (!randomize_on)
 154     return addr;
 155
 156   /* Otherwise, we need to try again with buffer space.  */
 157   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 158   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 159   if (buffer != (void *) MAP_FAILED)
 160     munmap (buffer, buffer_size);
 161   if (addr == (void *) MAP_FAILED)
 162     return NULL;
 163   munmap (addr, size);
 164
 165   return addr;
 166 }
 167
 168 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 169    mapping the data at BASE, -1 if we couldn't.
 170
 171    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 172    a specific START address on either hpux or linux.  First we see
 173    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 174    races.  If it doesn't, we try an anonymous private mmap since the
 175    kernel is more likely to honor the BASE address in anonymous maps.
 176    We then copy the data to the anonymous private map.  This assumes
 177    of course that we don't need to change the data in the PCH file
 178    after it is created.
 179
 180    This approach obviously causes a performance penalty but there is
 181    little else we can do given the current PCH implementation.  */
 182
 183 static int
 184 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 185 {
 186   void *addr;
 187
 188   /* We're called with size == 0 if we're not planning to load a PCH
 189      file at all.  This allows the hook to free any static space that
 190      we might have allocated at link time.  */
 191   if (size == 0)
 192     return -1;
 193
 194   /* Try to map the file with MAP_PRIVATE.  */
 195   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 196
 197   if (addr == base)
 198     return 1;
 199
 200   if (addr != (void *) MAP_FAILED)
 201     munmap (addr, size);
 202
 203   /* Try to make an anonymous private mmap at the desired location.  */
 204   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 205                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 206
 207   if (addr != base)
 208     {
 209       if (addr != (void *) MAP_FAILED)
 210         munmap (addr, size);
 211       return -1;
 212     }
 213
 214   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 215     return -1;
 216
 217   while (size)
 218     {
 219       ssize_t nbytes;
 220
 221       nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1));
 222       if (nbytes <= 0)
 223         return -1;
 224       base = (char *) base + nbytes;
 225       size -= nbytes;
 226     }
 227
 228   return 1;
 229 }
 230
 231 \f
 232 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;