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1 /* Linux host-specific hook definitions.
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111
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2 Copyright (C) 2004-2017 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 "hosthooks.h"
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24 #include "hosthooks-def.h"
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25
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26
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27 /* Linux has a feature called exec-shield-randomize that perturbs the
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28 address of non-fixed mapped segments by a (relatively) small amount.
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29 The feature is intended to make it harder to attack the system with
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30 buffer overflow attacks, since every invocation of a program will
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31 have its libraries and data segments at slightly different addresses.
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32
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33 This feature causes us problems with PCH because it makes it that
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34 much harder to acquire a stable location at which to map our PCH
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35 data file.
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36
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37 [ The feature causes other points of non-determinism within the
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38 compiler as well, so we'd *really* like to be able to have the
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39 driver disable exec-shield-randomize for the process group, but
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40 that isn't possible at present. ]
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41
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42 We're going to try several things:
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43
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44 * Select an architecture specific address as "likely" and see
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45 if that's free. For our 64-bit hosts, we can easily choose
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46 an address in Never Never Land.
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47
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48 * If exec-shield-randomize is disabled, then just use the
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49 address chosen by mmap in step one.
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50
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51 * If exec-shield-randomize is enabled, then temporarily allocate
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52 32M of memory as a buffer, then allocate PCH memory, then
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53 free the buffer. The theory here is that the perturbation is
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54 no more than 16M, and so by allocating our buffer larger than
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55 that we make it considerably more likely that the address will
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56 be free when we want to load the data back.
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57 */
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58
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59 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
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60 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
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61
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62 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
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63 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
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64
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65 /* For various ports, try to guess a fixed spot in the vm space
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66 that's probably free. */
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67 #if defined(__alpha)
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68 # define TRY_EMPTY_VM_SPACE 0x10000000000
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69 #elif defined(__ia64)
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70 # define TRY_EMPTY_VM_SPACE 0x2000000100000000
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111
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71 #elif defined(__x86_64) && defined(__LP64__)
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72 # define TRY_EMPTY_VM_SPACE 0x1000000000
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0
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73 #elif defined(__x86_64)
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111
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74 # define TRY_EMPTY_VM_SPACE 0x60000000
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0
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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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111
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89 #elif defined(__aarch64__) && defined(__ILP32__)
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90 # define TRY_EMPTY_VM_SPACE 0x60000000
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91 #elif defined(__aarch64__)
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92 # define TRY_EMPTY_VM_SPACE 0x1000000000
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93 #elif defined(__ARM_EABI__)
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94 # define TRY_EMPTY_VM_SPACE 0x60000000
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95 #elif defined(__mips__) && defined(__LP64__)
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96 # define TRY_EMPTY_VM_SPACE 0x8000000000
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97 #elif defined(__mips__)
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98 # define TRY_EMPTY_VM_SPACE 0x60000000
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0
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99 #else
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100 # define TRY_EMPTY_VM_SPACE 0
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101 #endif
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102
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103 /* Determine a location where we might be able to reliably allocate SIZE
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104 bytes. FD is the PCH file, though we should return with the file
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105 unmapped. */
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106
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107 static void *
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108 linux_gt_pch_get_address (size_t size, int fd)
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109 {
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110 size_t buffer_size = 32 * 1024 * 1024;
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111 void *addr, *buffer;
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112 FILE *f;
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113 bool randomize_on;
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114
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115 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
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116 MAP_PRIVATE, fd, 0);
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117
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118 /* If we failed the map, that means there's *no* free space. */
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119 if (addr == (void *) MAP_FAILED)
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120 return NULL;
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121 /* Unmap the area before returning. */
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122 munmap (addr, size);
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123
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124 /* If we got the exact area we requested, then that's great. */
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125 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
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126 return addr;
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127
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128 /* If we didn't, then we need to look to see if virtual address
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129 randomization is on. That is recorded in
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130 kernel.randomize_va_space. An older implementation used
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131 kernel.exec-shield-randomize. */
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132 f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
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133 if (f == NULL)
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134 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
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135 randomize_on = false;
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136 if (f != NULL)
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137 {
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138 char buf[100];
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139 size_t c;
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140
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141 c = fread (buf, 1, sizeof buf - 1, f);
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142 if (c > 0)
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143 {
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144 buf[c] = '\0';
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145 randomize_on = (atoi (buf) > 0);
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146 }
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147 fclose (f);
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148 }
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149
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150 /* If it isn't, then accept the address that mmap selected as fine. */
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151 if (!randomize_on)
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152 return addr;
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153
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154 /* Otherwise, we need to try again with buffer space. */
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155 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
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156 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
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157 if (buffer != (void *) MAP_FAILED)
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158 munmap (buffer, buffer_size);
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159 if (addr == (void *) MAP_FAILED)
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160 return NULL;
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161 munmap (addr, size);
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162
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163 return addr;
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164 }
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165
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166 /* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
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167 mapping the data at BASE, -1 if we couldn't.
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168
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169 It's not possibly to reliably mmap a file using MAP_PRIVATE to
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170 a specific START address on either hpux or linux. First we see
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171 if mmap with MAP_PRIVATE works. If it does, we are off to the
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172 races. If it doesn't, we try an anonymous private mmap since the
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173 kernel is more likely to honor the BASE address in anonymous maps.
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174 We then copy the data to the anonymous private map. This assumes
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175 of course that we don't need to change the data in the PCH file
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176 after it is created.
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177
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178 This approach obviously causes a performance penalty but there is
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179 little else we can do given the current PCH implementation. */
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180
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181 static int
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182 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
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183 {
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184 void *addr;
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185
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186 /* We're called with size == 0 if we're not planning to load a PCH
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187 file at all. This allows the hook to free any static space that
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188 we might have allocated at link time. */
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189 if (size == 0)
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190 return -1;
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191
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192 /* Try to map the file with MAP_PRIVATE. */
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193 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
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194
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195 if (addr == base)
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196 return 1;
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197
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198 if (addr != (void *) MAP_FAILED)
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199 munmap (addr, size);
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200
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201 /* Try to make an anonymous private mmap at the desired location. */
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202 addr = mmap (base, size, PROT_READ | PROT_WRITE,
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203 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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204
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205 if (addr != base)
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206 {
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207 if (addr != (void *) MAP_FAILED)
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208 munmap (addr, size);
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209 return -1;
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210 }
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211
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212 if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
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213 return -1;
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214
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215 while (size)
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216 {
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217 ssize_t nbytes;
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218
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111
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219 nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1));
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0
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220 if (nbytes <= 0)
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221 return -1;
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222 base = (char *) base + nbytes;
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223 size -= nbytes;
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224 }
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225
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226 return 1;
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227 }
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228
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229
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230 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;
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