220 lines
6.9 KiB
C
220 lines
6.9 KiB
C
/* Linux host-specific hook definitions.
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Copyright (C) 2004, 2005 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published
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by the Free Software Foundation; either version 2, or (at your
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option) any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to the
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Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include <sys/mman.h>
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#include <limits.h>
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#include "hosthooks.h"
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#include "hosthooks-def.h"
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/* Linux has a feature called exec-shield-randomize that perturbs the
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address of non-fixed mapped segments by a (relatively) small amount.
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The feature is intended to make it harder to attack the system with
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buffer overflow attacks, since every invocation of a program will
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have its libraries and data segments at slightly different addresses.
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This feature causes us problems with PCH because it makes it that
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much harder to acquire a stable location at which to map our PCH
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data file.
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[ The feature causes other points of non-determinism within the
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compiler as well, so we'd *really* like to be able to have the
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driver disable exec-shield-randomize for the process group, but
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that isn't possible at present. ]
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We're going to try several things:
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* Select an architecture specific address as "likely" and see
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if that's free. For our 64-bit hosts, we can easily choose
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an address in Never Never Land.
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* If exec-shield-randomize is disabled, then just use the
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address chosen by mmap in step one.
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* If exec-shield-randomize is enabled, then temporarily allocate
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32M of memory as a buffer, then allocate PCH memory, then
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free the buffer. The theory here is that the perturbation is
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no more than 16M, and so by allocating our buffer larger than
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that we make it considerably more likely that the address will
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be free when we want to load the data back.
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*/
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#undef HOST_HOOKS_GT_PCH_GET_ADDRESS
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#define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
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#undef HOST_HOOKS_GT_PCH_USE_ADDRESS
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#define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
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/* For various ports, try to guess a fixed spot in the vm space
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that's probably free. */
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#if defined(__alpha)
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# define TRY_EMPTY_VM_SPACE 0x10000000000
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#elif defined(__ia64)
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# define TRY_EMPTY_VM_SPACE 0x2000000100000000
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#elif defined(__x86_64)
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# define TRY_EMPTY_VM_SPACE 0x1000000000
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#elif defined(__i386)
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# define TRY_EMPTY_VM_SPACE 0x60000000
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#elif defined(__powerpc__)
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# define TRY_EMPTY_VM_SPACE 0x60000000
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#elif defined(__s390x__)
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# define TRY_EMPTY_VM_SPACE 0x8000000000
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#elif defined(__s390__)
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# define TRY_EMPTY_VM_SPACE 0x60000000
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#elif defined(__sparc__) && defined(__LP64__)
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# define TRY_EMPTY_VM_SPACE 0x8000000000
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#elif defined(__sparc__)
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# define TRY_EMPTY_VM_SPACE 0x60000000
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#else
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# define TRY_EMPTY_VM_SPACE 0
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#endif
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/* Determine a location where we might be able to reliably allocate SIZE
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bytes. FD is the PCH file, though we should return with the file
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unmapped. */
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static void *
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linux_gt_pch_get_address (size_t size, int fd)
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{
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size_t buffer_size = 32 * 1024 * 1024;
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void *addr, *buffer;
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FILE *f;
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bool randomize_on;
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addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
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MAP_PRIVATE, fd, 0);
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/* If we failed the map, that means there's *no* free space. */
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if (addr == (void *) MAP_FAILED)
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return NULL;
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/* Unmap the area before returning. */
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munmap (addr, size);
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/* If we got the exact area we requested, then that's great. */
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if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
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return addr;
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/* If we didn't, then we need to look to see if virtual address
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randomization is on. That is recorded in
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kernel.randomize_va_space. An older implementation used
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kernel.exec-shield-randomize. */
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f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
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if (f == NULL)
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f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
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randomize_on = false;
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if (f != NULL)
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{
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char buf[100];
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size_t c;
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c = fread (buf, 1, sizeof buf - 1, f);
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if (c > 0)
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{
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buf[c] = '\0';
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randomize_on = (atoi (buf) > 0);
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}
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fclose (f);
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}
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/* If it isn't, then accept the address that mmap selected as fine. */
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if (!randomize_on)
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return addr;
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/* Otherwise, we need to try again with buffer space. */
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buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
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addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
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if (buffer != (void *) MAP_FAILED)
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munmap (buffer, buffer_size);
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if (addr == (void *) MAP_FAILED)
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return NULL;
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munmap (addr, size);
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return addr;
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}
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/* Map SIZE bytes of FD+OFFSET at BASE. Return 1 if we succeeded at
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mapping the data at BASE, -1 if we couldn't.
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It's not possibly to reliably mmap a file using MAP_PRIVATE to
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a specific START address on either hpux or linux. First we see
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if mmap with MAP_PRIVATE works. If it does, we are off to the
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races. If it doesn't, we try an anonymous private mmap since the
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kernel is more likely to honor the BASE address in anonymous maps.
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We then copy the data to the anonymous private map. This assumes
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of course that we don't need to change the data in the PCH file
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after it is created.
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This approach obviously causes a performance penalty but there is
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little else we can do given the current PCH implementation. */
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static int
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linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
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{
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void *addr;
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/* We're called with size == 0 if we're not planning to load a PCH
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file at all. This allows the hook to free any static space that
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we might have allocated at link time. */
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if (size == 0)
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return -1;
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/* Try to map the file with MAP_PRIVATE. */
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addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
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if (addr == base)
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return 1;
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if (addr != (void *) MAP_FAILED)
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munmap (addr, size);
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/* Try to make an anonymous private mmap at the desired location. */
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addr = mmap (base, size, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (addr != base)
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{
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if (addr != (void *) MAP_FAILED)
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munmap (addr, size);
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return -1;
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}
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if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
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return -1;
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while (size)
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{
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ssize_t nbytes;
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nbytes = read (fd, base, MIN (size, SSIZE_MAX));
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if (nbytes <= 0)
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return -1;
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base = (char *) base + nbytes;
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size -= nbytes;
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}
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return 1;
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}
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const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;
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