host-linux.c revision 1.9
1/* Linux host-specific hook definitions. 2 Copyright (C) 2004-2018 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#else 100# define TRY_EMPTY_VM_SPACE 0 101#endif 102 103/* Determine a location where we might be able to reliably allocate SIZE 104 bytes. FD is the PCH file, though we should return with the file 105 unmapped. */ 106 107static void * 108linux_gt_pch_get_address (size_t size, int fd) 109{ 110 size_t buffer_size = 32 * 1024 * 1024; 111 void *addr, *buffer; 112 FILE *f; 113 bool randomize_on; 114 115 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE, 116 MAP_PRIVATE, fd, 0); 117 118 /* If we failed the map, that means there's *no* free space. */ 119 if (addr == (void *) MAP_FAILED) 120 return NULL; 121 /* Unmap the area before returning. */ 122 munmap (addr, size); 123 124 /* If we got the exact area we requested, then that's great. */ 125 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE) 126 return addr; 127 128 /* If we didn't, then we need to look to see if virtual address 129 randomization is on. That is recorded in 130 kernel.randomize_va_space. An older implementation used 131 kernel.exec-shield-randomize. */ 132 f = fopen ("/proc/sys/kernel/randomize_va_space", "r"); 133 if (f == NULL) 134 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r"); 135 randomize_on = false; 136 if (f != NULL) 137 { 138 char buf[100]; 139 size_t c; 140 141 c = fread (buf, 1, sizeof buf - 1, f); 142 if (c > 0) 143 { 144 buf[c] = '\0'; 145 randomize_on = (atoi (buf) > 0); 146 } 147 fclose (f); 148 } 149 150 /* If it isn't, then accept the address that mmap selected as fine. */ 151 if (!randomize_on) 152 return addr; 153 154 /* Otherwise, we need to try again with buffer space. */ 155 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0); 156 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); 157 if (buffer != (void *) MAP_FAILED) 158 munmap (buffer, buffer_size); 159 if (addr == (void *) MAP_FAILED) 160 return NULL; 161 munmap (addr, size); 162 163 return addr; 164} 165 166/* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at 167 mapping the data at BASE, -1 if we couldn't. 168 169 It's not possibly to reliably mmap a file using MAP_PRIVATE to 170 a specific START address on either hpux or linux. First we see 171 if mmap with MAP_PRIVATE works. If it does, we are off to the 172 races. If it doesn't, we try an anonymous private mmap since the 173 kernel is more likely to honor the BASE address in anonymous maps. 174 We then copy the data to the anonymous private map. This assumes 175 of course that we don't need to change the data in the PCH file 176 after it is created. 177 178 This approach obviously causes a performance penalty but there is 179 little else we can do given the current PCH implementation. */ 180 181static int 182linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset) 183{ 184 void *addr; 185 186 /* We're called with size == 0 if we're not planning to load a PCH 187 file at all. This allows the hook to free any static space that 188 we might have allocated at link time. */ 189 if (size == 0) 190 return -1; 191 192 /* Try to map the file with MAP_PRIVATE. */ 193 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset); 194 195 if (addr == base) 196 return 1; 197 198 if (addr != (void *) MAP_FAILED) 199 munmap (addr, size); 200 201 /* Try to make an anonymous private mmap at the desired location. */ 202 addr = mmap (base, size, PROT_READ | PROT_WRITE, 203 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); 204 205 if (addr != base) 206 { 207 if (addr != (void *) MAP_FAILED) 208 munmap (addr, size); 209 return -1; 210 } 211 212 if (lseek (fd, offset, SEEK_SET) == (off_t)-1) 213 return -1; 214 215 while (size) 216 { 217 ssize_t nbytes; 218 219 nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1)); 220 if (nbytes <= 0) 221 return -1; 222 base = (char *) base + nbytes; 223 size -= nbytes; 224 } 225 226 return 1; 227} 228 229 230const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER; 231