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1 /* Linux host-specific hook definitions.
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2 Copyright (C) 2004, 2005, 2007, 2008 Free Software Foundation, Inc.
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify it
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7 under the terms of the GNU General Public License as published
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8 by the Free Software Foundation; either version 3, or (at your
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9 option) any later version.
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10
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11 GCC is distributed in the hope that it will be useful, but WITHOUT
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12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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13 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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14 License for more details.
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15
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16 You should have received a copy of the GNU General Public License
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17 along with GCC; see the file COPYING3. If not see
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18 <http://www.gnu.org/licenses/>. */
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19
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20 #include "config.h"
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21 #include "system.h"
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22 #include "coretypes.h"
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23 #include <sys/mman.h>
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24 #include <limits.h>
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25 #include "hosthooks.h"
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26 #include "hosthooks-def.h"
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27
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28
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29 /* Linux has a feature called exec-shield-randomize that perturbs the
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30 address of non-fixed mapped segments by a (relatively) small amount.
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31 The feature is intended to make it harder to attack the system with
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32 buffer overflow attacks, since every invocation of a program will
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33 have its libraries and data segments at slightly different addresses.
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34
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35 This feature causes us problems with PCH because it makes it that
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36 much harder to acquire a stable location at which to map our PCH
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37 data file.
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38
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39 [ The feature causes other points of non-determinism within the
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40 compiler as well, so we'd *really* like to be able to have the
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41 driver disable exec-shield-randomize for the process group, but
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42 that isn't possible at present. ]
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43
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44 We're going to try several things:
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45
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46 * Select an architecture specific address as "likely" and see
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47 if that's free. For our 64-bit hosts, we can easily choose
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48 an address in Never Never Land.
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49
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50 * If exec-shield-randomize is disabled, then just use the
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51 address chosen by mmap in step one.
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52
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53 * If exec-shield-randomize is enabled, then temporarily allocate
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54 32M of memory as a buffer, then allocate PCH memory, then
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55 free the buffer. The theory here is that the perturbation is
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56 no more than 16M, and so by allocating our buffer larger than
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57 that we make it considerably more likely that the address will
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58 be free when we want to load the data back.
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59 */
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60
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61 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
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62 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
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63
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64 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
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65 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
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66
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67 /* For various ports, try to guess a fixed spot in the vm space
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68 that's probably free. */
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69 #if defined(__alpha)
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70 # define TRY_EMPTY_VM_SPACE 0x10000000000
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71 #elif defined(__ia64)
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72 # define TRY_EMPTY_VM_SPACE 0x2000000100000000
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73 #elif defined(__x86_64)
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74 # define TRY_EMPTY_VM_SPACE 0x1000000000
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75 #elif defined(__i386)
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76 # define TRY_EMPTY_VM_SPACE 0x60000000
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77 #elif defined(__powerpc__)
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78 # define TRY_EMPTY_VM_SPACE 0x60000000
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79 #elif defined(__s390x__)
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80 # define TRY_EMPTY_VM_SPACE 0x8000000000
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81 #elif defined(__s390__)
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82 # define TRY_EMPTY_VM_SPACE 0x60000000
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83 #elif defined(__sparc__) && defined(__LP64__)
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84 # define TRY_EMPTY_VM_SPACE 0x8000000000
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85 #elif defined(__sparc__)
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86 # define TRY_EMPTY_VM_SPACE 0x60000000
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87 #elif defined(__mc68000__)
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88 # define TRY_EMPTY_VM_SPACE 0x40000000
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89 #else
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90 # define TRY_EMPTY_VM_SPACE 0
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91 #endif
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92
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93 /* Determine a location where we might be able to reliably allocate SIZE
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94 bytes. FD is the PCH file, though we should return with the file
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95 unmapped. */
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96
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97 static void *
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98 linux_gt_pch_get_address (size_t size, int fd)
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99 {
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100 size_t buffer_size = 32 * 1024 * 1024;
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101 void *addr, *buffer;
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102 FILE *f;
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103 bool randomize_on;
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104
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105 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
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106 MAP_PRIVATE, fd, 0);
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107
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108 /* If we failed the map, that means there's *no* free space. */
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109 if (addr == (void *) MAP_FAILED)
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110 return NULL;
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111 /* Unmap the area before returning. */
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112 munmap (addr, size);
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113
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114 /* If we got the exact area we requested, then that's great. */
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115 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
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116 return addr;
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117
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118 /* If we didn't, then we need to look to see if virtual address
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119 randomization is on. That is recorded in
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120 kernel.randomize_va_space. An older implementation used
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121 kernel.exec-shield-randomize. */
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122 f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
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123 if (f == NULL)
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124 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
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125 randomize_on = false;
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126 if (f != NULL)
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127 {
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128 char buf[100];
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129 size_t c;
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130
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131 c = fread (buf, 1, sizeof buf - 1, f);
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132 if (c > 0)
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133 {
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134 buf[c] = '\0';
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135 randomize_on = (atoi (buf) > 0);
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136 }
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137 fclose (f);
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138 }
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139
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140 /* If it isn't, then accept the address that mmap selected as fine. */
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141 if (!randomize_on)
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142 return addr;
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143
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144 /* Otherwise, we need to try again with buffer space. */
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145 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
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146 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
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147 if (buffer != (void *) MAP_FAILED)
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148 munmap (buffer, buffer_size);
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149 if (addr == (void *) MAP_FAILED)
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150 return NULL;
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151 munmap (addr, size);
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152
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153 return addr;
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154 }
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155
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156 /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
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157 mapping the data at BASE, -1 if we couldn't.
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158
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159 It's not possibly to reliably mmap a file using MAP_PRIVATE to
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160 a specific START address on either hpux or linux. First we see
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161 if mmap with MAP_PRIVATE works. If it does, we are off to the
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162 races. If it doesn't, we try an anonymous private mmap since the
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163 kernel is more likely to honor the BASE address in anonymous maps.
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164 We then copy the data to the anonymous private map. This assumes
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165 of course that we don't need to change the data in the PCH file
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166 after it is created.
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167
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168 This approach obviously causes a performance penalty but there is
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169 little else we can do given the current PCH implementation. */
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170
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171 static int
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172 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
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173 {
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174 void *addr;
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175
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176 /* We're called with size == 0 if we're not planning to load a PCH
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177 file at all. This allows the hook to free any static space that
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178 we might have allocated at link time. */
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179 if (size == 0)
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180 return -1;
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181
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182 /* Try to map the file with MAP_PRIVATE. */
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183 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
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184
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185 if (addr == base)
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186 return 1;
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187
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188 if (addr != (void *) MAP_FAILED)
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189 munmap (addr, size);
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190
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191 /* Try to make an anonymous private mmap at the desired location. */
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192 addr = mmap (base, size, PROT_READ | PROT_WRITE,
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193 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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194
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195 if (addr != base)
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196 {
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197 if (addr != (void *) MAP_FAILED)
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198 munmap (addr, size);
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199 return -1;
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200 }
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201
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202 if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
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203 return -1;
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204
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205 while (size)
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206 {
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207 ssize_t nbytes;
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208
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209 nbytes = read (fd, base, MIN (size, SSIZE_MAX));
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210 if (nbytes <= 0)
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211 return -1;
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212 base = (char *) base + nbytes;
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213 size -= nbytes;
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214 }
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215
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216 return 1;
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217 }
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218
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219
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220 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;
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