gcc/config/host-linux.cc

   1 /* Linux host-specific hook definitions.
   2    Copyright (C) 2004-2022 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 #elif defined(__loongarch__) && defined(__LP64__)
 102 # define TRY_EMPTY_VM_SPACE     0x8000000000
 103 #else
 104 # define TRY_EMPTY_VM_SPACE     0
 105 #endif
 106
 107 /* Determine a location where we might be able to reliably allocate SIZE
 108    bytes.  FD is the PCH file, though we should return with the file
 109    unmapped.  */
 110
 111 static void *
 112 linux_gt_pch_get_address (size_t size, int fd)
 113 {
 114   size_t buffer_size = 32 * 1024 * 1024;
 115   void *addr, *buffer;
 116   FILE *f;
 117   bool randomize_on;
 118
 119   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 120                MAP_PRIVATE, fd, 0);
 121
 122   /* If we failed the map, that means there's *no* free space.  */
 123   if (addr == (void *) MAP_FAILED)
 124     return NULL;
 125   /* Unmap the area before returning.  */
 126   munmap (addr, size);
 127
 128   /* If we got the exact area we requested, then that's great.  */
 129   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 130     return addr;
 131
 132   /* If we didn't, then we need to look to see if virtual address
 133      randomization is on.  That is recorded in
 134      kernel.randomize_va_space.  An older implementation used
 135      kernel.exec-shield-randomize.  */
 136   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 137   if (f == NULL)
 138     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 139   randomize_on = false;
 140   if (f != NULL)
 141     {
 142       char buf[100];
 143       size_t c;
 144
 145       c = fread (buf, 1, sizeof buf - 1, f);
 146       if (c > 0)
 147         {
 148           buf[c] = '\0';
 149           randomize_on = (atoi (buf) > 0);
 150         }
 151       fclose (f);
 152     }
 153
 154   /* If it isn't, then accept the address that mmap selected as fine.  */
 155   if (!randomize_on)
 156     return addr;
 157
 158   /* Otherwise, we need to try again with buffer space.  */
 159   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 160   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 161   if (buffer != (void *) MAP_FAILED)
 162     munmap (buffer, buffer_size);
 163   if (addr == (void *) MAP_FAILED)
 164     return NULL;
 165   munmap (addr, size);
 166
 167   return addr;
 168 }
 169
 170 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 171    mapping the data at BASE, -1 if we couldn't.
 172
 173    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 174    a specific START address on either hpux or linux.  First we see
 175    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 176    races.  If it doesn't, we try an anonymous private mmap since the
 177    kernel is more likely to honor the BASE address in anonymous maps.
 178    We then copy the data to the anonymous private map.  This assumes
 179    of course that we don't need to change the data in the PCH file
 180    after it is created.
 181
 182    This approach obviously causes a performance penalty but there is
 183    little else we can do given the current PCH implementation.  */
 184
 185 static int
 186 linux_gt_pch_use_address (void *&base, size_t size, int fd, size_t offset)
 187 {
 188   void *addr;
 189
 190   /* We're called with size == 0 if we're not planning to load a PCH
 191      file at all.  This allows the hook to free any static space that
 192      we might have allocated at link time.  */
 193   if (size == 0)
 194     return -1;
 195
 196   /* Try to map the file with MAP_PRIVATE.  */
 197   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 198
 199   if (addr == base)
 200     return 1;
 201
 202   if (addr != (void *) MAP_FAILED)
 203     munmap (addr, size);
 204
 205   /* Try to make an anonymous private mmap at the desired location.  */
 206   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 207                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 208
 209   if (addr == (void *) MAP_FAILED)
 210     return -1;
 211
 212   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 213     return -1;
 214
 215   base = addr;
 216
 217   while (size)
 218     {
 219       ssize_t nbytes;
 220
 221       nbytes = read (fd, addr, MIN (size, (size_t)-1 >> 1));
 222       if (nbytes <= 0)
 223         return -1;
 224       addr = (char *) addr + nbytes;
 225       size -= nbytes;
 226     }
 227
 228   return 1;
 229 }
 230
 231 \f
 232 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;