/* Linux <limits.h> #include "hosthooks.h" #include "hosthooks-def.h" /* Linux has a feature called exec-shield-randomize that perturbs the address of non-fixed mapped segments by a (relatively) small amount. The feature is intended to make it harder to attack the system with buffer overflow attacks, since every invocation of a program will have its libraries and data segments at slightly different addresses. This feature causes us problems with PCH because it makes it that much harder to acquire a stable location at which to map our PCH data file. [ The feature causes other points of non-determinism within the compiler as well, so we'd *really* like to be able to have the driver disable exec-shield-randomize for the process group, but that isn't possible at present. ] We're going to try several things: * Select an architecture specific address as "likely" and see if that's free. For our 64-bit hosts, we can easily choose an address in Never Never Land. * If exec-shield-randomize is disabled, then just use the address chosen by mmap in step one. * If exec-shield-randomize is enabled, then temporarily allocate 32M of memory as a buffer, then allocate PCH memory, then free the buffer. The theory here is that the perturbation is no more than 16M, and so by allocating our buffer larger than that we make it considerably more likely that the address will be free when we want to load the data back. */ #undef HOST_HOOKS_GT_PCH_GET_ADDRESS #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address #undef HOST_HOOKS_GT_PCH_USE_ADDRESS #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address /* For various ports, try to guess a fixed spot in the vm space that's probably free. */ #if defined(__alpha) # define TRY_EMPTY_VM_SPACE 0x10000000000 #elif defined(__ia64) # define TRY_EMPTY_VM_SPACE 0x2000000100000000 #elif defined(__x86_64) # define TRY_EMPTY_VM_SPACE 0x1000000000 #elif defined(__i386) # define TRY_EMPTY_VM_SPACE 0x60000000 #elif defined(__powerpc__) # define TRY_EMPTY_VM_SPACE 0x60000000 #elif defined(__s390x__) # define TRY_EMPTY_VM_SPACE 0x8000000000 #elif defined(__s390__) # define TRY_EMPTY_VM_SPACE 0x60000000 #elif defined(__sparc__) && defined(__LP64__) # define TRY_EMPTY_VM_SPACE 0x8000000000 #elif defined(__sparc__) # define TRY_EMPTY_VM_SPACE 0x60000000 #else # define TRY_EMPTY_VM_SPACE 0 #endif /* Determine a location where we might be able to reliably allocate SIZE bytes. FD is the PCH file, though we should return with the file unmapped. */ static void * linux_gt_pch_get_address (size_t size, int fd) { size_t buffer_size = 32 * 1024 * 1024; void *addr, *buffer; FILE *f; bool randomize_on; addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); /* If we failed the map, that means there's *no* free space. */ if (addr == (void *) MAP_FAILED) return NULL; /* Unmap the area before returning. */ munmap (addr, size); /* If we got the exact area we requested, then that's great. */ if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE) return addr; /* If we didn't, then we need to look to see if virtual address randomization is on. That is recorded in kernel.randomize_va_space. An older implementation used kernel.exec-shield-randomize. */ f = fopen ("/proc/sys/kernel/randomize_va_space", "r"); if (f == NULL) f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r"); randomize_on = false; if (f != NULL) { char buf[100]; size_t c; c = fread (buf, 1, sizeof buf - 1, f); if (c > 0) { buf[c] = '\0'; randomize_on = (atoi (buf) > 0); } fclose (f); } /* If it isn't, then accept the address that mmap selected as fine. */ if (!randomize_on) return addr; /* Otherwise, we need to try again with buffer space. */ buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0); addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); if (buffer != (void *) MAP_FAILED) munmap (buffer, buffer_size); if (addr == (void *) MAP_FAILED) return NULL; linux;