host-linux.c revision 1.1.1.1.4.2
1/* Linux host-specific hook definitions. 2 Copyright (C) 2004, 2005, 2007, 2008 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 <sys/mman.h> 24#include <limits.h> 25#include "hosthooks.h" 26#include "hosthooks-def.h" 27 28 29/* Linux has a feature called exec-shield-randomize that perturbs the 30 address of non-fixed mapped segments by a (relatively) small amount. 31 The feature is intended to make it harder to attack the system with 32 buffer overflow attacks, since every invocation of a program will 33 have its libraries and data segments at slightly different addresses. 34 35 This feature causes us problems with PCH because it makes it that 36 much harder to acquire a stable location at which to map our PCH 37 data file. 38 39 [ The feature causes other points of non-determinism within the 40 compiler as well, so we'd *really* like to be able to have the 41 driver disable exec-shield-randomize for the process group, but 42 that isn't possible at present. ] 43 44 We're going to try several things: 45 46 * Select an architecture specific address as "likely" and see 47 if that's free. For our 64-bit hosts, we can easily choose 48 an address in Never Never Land. 49 50 * If exec-shield-randomize is disabled, then just use the 51 address chosen by mmap in step one. 52 53 * If exec-shield-randomize is enabled, then temporarily allocate 54 32M of memory as a buffer, then allocate PCH memory, then 55 free the buffer. The theory here is that the perturbation is 56 no more than 16M, and so by allocating our buffer larger than 57 that we make it considerably more likely that the address will 58 be free when we want to load the data back. 59*/ 60 61#undef HOST_HOOKS_GT_PCH_GET_ADDRESS 62#define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address 63 64#undef HOST_HOOKS_GT_PCH_USE_ADDRESS 65#define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address 66 67/* For various ports, try to guess a fixed spot in the vm space 68 that's probably free. */ 69#if defined(__alpha) 70# define TRY_EMPTY_VM_SPACE 0x10000000000 71#elif defined(__ia64) 72# define TRY_EMPTY_VM_SPACE 0x2000000100000000 73#elif defined(__x86_64) 74# define TRY_EMPTY_VM_SPACE 0x1000000000 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#else 90# define TRY_EMPTY_VM_SPACE 0 91#endif 92 93/* Determine a location where we might be able to reliably allocate SIZE 94 bytes. FD is the PCH file, though we should return with the file 95 unmapped. */ 96 97static void * 98linux_gt_pch_get_address (size_t size, int fd) 99{ 100 size_t buffer_size = 32 * 1024 * 1024; 101 void *addr, *buffer; 102 FILE *f; 103 bool randomize_on; 104 105 addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE, 106 MAP_PRIVATE, fd, 0); 107 108 /* If we failed the map, that means there's *no* free space. */ 109 if (addr == (void *) MAP_FAILED) 110 return NULL; 111 /* Unmap the area before returning. */ 112 munmap (addr, size); 113 114 /* If we got the exact area we requested, then that's great. */ 115 if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE) 116 return addr; 117 118 /* If we didn't, then we need to look to see if virtual address 119 randomization is on. That is recorded in 120 kernel.randomize_va_space. An older implementation used 121 kernel.exec-shield-randomize. */ 122 f = fopen ("/proc/sys/kernel/randomize_va_space", "r"); 123 if (f == NULL) 124 f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r"); 125 randomize_on = false; 126 if (f != NULL) 127 { 128 char buf[100]; 129 size_t c; 130 131 c = fread (buf, 1, sizeof buf - 1, f); 132 if (c > 0) 133 { 134 buf[c] = '\0'; 135 randomize_on = (atoi (buf) > 0); 136 } 137 fclose (f); 138 } 139 140 /* If it isn't, then accept the address that mmap selected as fine. */ 141 if (!randomize_on) 142 return addr; 143 144 /* Otherwise, we need to try again with buffer space. */ 145 buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0); 146 addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); 147 if (buffer != (void *) MAP_FAILED) 148 munmap (buffer, buffer_size); 149 if (addr == (void *) MAP_FAILED) 150 return NULL; 151 munmap (addr, size); 152 153 return addr; 154} 155 156/* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at 157 mapping the data at BASE, -1 if we couldn't. 158 159 It's not possibly to reliably mmap a file using MAP_PRIVATE to 160 a specific START address on either hpux or linux. First we see 161 if mmap with MAP_PRIVATE works. If it does, we are off to the 162 races. If it doesn't, we try an anonymous private mmap since the 163 kernel is more likely to honor the BASE address in anonymous maps. 164 We then copy the data to the anonymous private map. This assumes 165 of course that we don't need to change the data in the PCH file 166 after it is created. 167 168 This approach obviously causes a performance penalty but there is 169 little else we can do given the current PCH implementation. */ 170 171static int 172linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset) 173{ 174 void *addr; 175 176 /* We're called with size == 0 if we're not planning to load a PCH 177 file at all. This allows the hook to free any static space that 178 we might have allocated at link time. */ 179 if (size == 0) 180 return -1; 181 182 /* Try to map the file with MAP_PRIVATE. */ 183 addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset); 184 185 if (addr == base) 186 return 1; 187 188 if (addr != (void *) MAP_FAILED) 189 munmap (addr, size); 190 191 /* Try to make an anonymous private mmap at the desired location. */ 192 addr = mmap (base, size, PROT_READ | PROT_WRITE, 193 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); 194 195 if (addr != base) 196 { 197 if (addr != (void *) MAP_FAILED) 198 munmap (addr, size); 199 return -1; 200 } 201 202 if (lseek (fd, offset, SEEK_SET) == (off_t)-1) 203 return -1; 204 205 while (size) 206 { 207 ssize_t nbytes; 208 209 nbytes = read (fd, base, MIN (size, SSIZE_MAX)); 210 if (nbytes <= 0) 211 return -1; 212 base = (char *) base + nbytes; 213 size -= nbytes; 214 } 215 216 return 1; 217} 218 219 220const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER; 221