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improved ASLR (issue #372)

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This commit is contained in:
Daan Leijen 2021-02-24 15:14:17 -08:00
parent 3228bb685f
commit 9317256a4f
2 changed files with 19 additions and 2 deletions
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11
src/os.c
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@ -465,10 +465,17 @@ static void* mi_unix_mmap(void* addr, size_t size, size_t try_alignment, int pro
#if (MI_INTPTR_SIZE >= 8) && (defined(_WIN32) || (defined(MI_OS_USE_MMAP) && !defined(MAP_ALIGNED)))
static mi_decl_cache_align _Atomic(uintptr_t) aligned_base;
// Return a 4MiB aligned address that is probably available
static void* mi_os_get_aligned_hint(size_t try_alignment, size_t size) {
// Return a 4MiB aligned address that is probably available.
// If this returns NULL, the OS will determine the address but on some OS's that may not be
// properly aligned which can be more costly as it needs to be adjusted afterwards.
// For a size > 4GiB this always returns NULL in order to guarantee good ASLR randomization;
// otherwise an initial large allocation of say 2TiB has a 50% chance to include (known) addresses
// in the middle of the 4TiB - 8TiB address range (see issue #372).
static void* mi_os_get_aligned_hint(size_t try_alignment, size_t size)
{
if (try_alignment == 0 || try_alignment > MI_SEGMENT_SIZE) return NULL;
if ((size%MI_SEGMENT_SIZE) != 0) return NULL;
if (size > 1*GiB) return NULL; // guarantee the chance of fixed valid address is at most 1/(4<<40 / 1<<30) = 1/4096.
uintptr_t hint = mi_atomic_add_acq_rel(&aligned_base, size);
if (hint == 0 || hint > ((intptr_t)30<<40)) { // try to wrap around after 30TiB (area after 32TiB is used for huge OS pages)
uintptr_t init = ((uintptr_t)4 << 40); // start at 4TiB area

10
test/main-override.cpp
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@ -32,6 +32,7 @@ void heap_late_free(); // issue #204
void padding_shrink(); // issue #209
void various_tests();
void test_mt_shutdown();
void fail_aslr(); // issue #372
int main() {
mi_stats_reset(); // ignore earlier allocations
@ -41,6 +42,7 @@ int main() {
padding_shrink();
various_tests();
//test_mt_shutdown();
//test_aslr();
mi_stats_print(NULL);
return 0;
}
@ -207,3 +209,11 @@ void test_mt_shutdown()
std::cout << "done" << std::endl;
}
// issue #372
void fail_aslr() {
size_t sz = (4ULL << 40); // 4TiB
void* p = malloc(sz);
printf("pointer p: %p: area up to %p\n", p, (uint8_t*)p + sz);
*(int*)0x7FFFFFFF000 = 0; // should segfault
}