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byte-precise heap block overflow checking with encoded padding

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daan 2020-01-31 23:39:51 -08:00
parent 68112a2751
commit 40f1e1e07b
7 changed files with 138 additions and 50 deletions
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135
src/alloc.c
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@ -21,7 +21,7 @@ terms of the MIT license. A copy of the license can be found in the file
// Fast allocation in a page: just pop from the free list.
// Fall back to generic allocation only if the list is empty.
extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t size) mi_attr_noexcept {
extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t size) mi_attr_noexcept {
mi_assert_internal(page->xblock_size==0||mi_page_block_size(page) >= size);
mi_block_t* block = page->free;
if (mi_unlikely(block == NULL)) {
@ -29,25 +29,29 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
}
mi_assert_internal(block != NULL && _mi_ptr_page(block) == page);
// pop from the free list
page->free = mi_block_next(page,block);
page->free = mi_block_next(page, block);
page->used++;
mi_assert_internal(page->free == NULL || _mi_ptr_page(page->free) == page);
#if (MI_DEBUG!=0)
#if (MI_DEBUG>0)
if (!page->is_zero) { memset(block, MI_DEBUG_UNINIT, size); }
#elif (MI_SECURE!=0)
block->next = 0; // don't leak internal data
#endif
#if (MI_STAT>1)
const size_t bsize = mi_page_usable_block_size(page);
if(bsize <= MI_LARGE_OBJ_SIZE_MAX) {
if (bsize <= MI_LARGE_OBJ_SIZE_MAX) {
const size_t bin = _mi_bin(bsize);
mi_heap_stat_increase(heap,normal[bin], 1);
mi_heap_stat_increase(heap, normal[bin], 1);
}
#endif
#if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
mi_assert_internal((MI_PADDING_SIZE % sizeof(mi_block_t*)) == 0);
mi_block_t* const padding = (mi_block_t*)((uint8_t*)block + mi_page_usable_block_size(page));
mi_block_set_nextx(page, padding, block, page->key[0], page->key[1]);
mi_padding_t* const padding = (mi_padding_t*)((uint8_t*)block + mi_page_usable_block_size(page));
ptrdiff_t delta = ((uint8_t*)padding - (uint8_t*)block - (size - MI_PADDING_SIZE));
mi_assert_internal(delta >= 0 && mi_page_usable_block_size(page) >= (size - MI_PADDING_SIZE + delta));
padding->block = (uint32_t)(((uintptr_t)block >> MI_INTPTR_SHIFT) ^ page->key[0]);
padding->delta = (uint32_t)(delta ^ page->key[1]);
uint8_t* fill = (uint8_t*)padding - delta;
for (ptrdiff_t i = 0; i < delta; i++) { fill[i] = MI_DEBUG_PADDING; }
#endif
return block;
}
@ -101,18 +105,18 @@ extern inline mi_decl_allocator void* mi_malloc(size_t size) mi_attr_noexcept {
void _mi_block_zero_init(const mi_page_t* page, void* p, size_t size) {
// note: we need to initialize the whole usable block size to zero, not just the requested size,
// or the recalloc/rezalloc functions cannot safely expand in place (see issue #63)
UNUSED_RELEASE(size);
UNUSED(size);
mi_assert_internal(p != NULL);
mi_assert_internal(mi_usable_size(p) >= size); // size can be zero
mi_assert_internal(_mi_ptr_page(p)==page);
if (page->is_zero) {
// already zero initialized memory?
((mi_block_t*)p)->next = 0; // clear the free list pointer
mi_assert_expensive(mi_mem_is_zero(p, mi_page_usable_block_size(page)));
mi_assert_expensive(mi_mem_is_zero(p, mi_usable_size(p)));
}
else {
// otherwise memset
memset(p, 0, mi_page_usable_block_size(page));
memset(p, 0, mi_usable_size(p));
}
}
@ -189,20 +193,82 @@ static inline bool mi_check_is_double_free(const mi_page_t* page, const mi_block
}
#endif
// ---------------------------------------------------------------------------
// Check for heap block overflow by setting up padding at the end of the block
// ---------------------------------------------------------------------------
#if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
mi_block_t* const padding = (mi_block_t*)((uint8_t*)block + mi_page_usable_block_size(page));
mi_block_t* const decoded = mi_block_nextx(page, padding, page->key[0], page->key[1]);
if (decoded != block) {
const ptrdiff_t size = (uint8_t*)padding - (uint8_t*)block;
_mi_error_message(EFAULT, "buffer overflow in heap block %p: write after %zd bytes\n", block, size );
static mi_padding_t mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* bsize) {
*bsize = mi_page_usable_block_size(page);
const mi_padding_t* const padding = (mi_padding_t*)((uint8_t*)block + *bsize);
mi_padding_t pad;
pad.block = padding->block ^ (uint32_t)page->key[0];
pad.delta = padding->delta ^ (uint32_t)page->key[1];
return pad;
}
// Return the exact usable size of a block.
static size_t mi_page_usable_size_of(const mi_page_t* page, const mi_block_t* block) {
size_t bsize;
mi_padding_t pad = mi_page_decode_padding(page, block, &bsize);
return bsize - pad.delta;
}
static bool mi_verify_padding(const mi_page_t* page, const mi_block_t* block, size_t* size, size_t* wrong) {
size_t bsize;
const mi_padding_t pad = mi_page_decode_padding(page, block, &bsize);
*size = *wrong = bsize;
if ((uint32_t)((uintptr_t)block >> MI_INTPTR_SHIFT) != pad.block) return false;
if (pad.delta > bsize) return false; // can be equal for zero-sized allocation!
*size = bsize - pad.delta;
uint8_t* fill = (uint8_t*)block + bsize - pad.delta;
for (uint32_t i = 0; i < pad.delta; i++) {
if (fill[i] != MI_DEBUG_PADDING) {
*wrong = bsize - pad.delta + i;
return false;
}
}
return true;
}
static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
size_t size;
size_t wrong;
if (!mi_verify_padding(page,block,&size,&wrong)) {
_mi_error_message(EFAULT, "buffer overflow in heap block %p of size %zu: write after %zu bytes\n", block, size, wrong );
}
}
// When a non-thread-local block is freed, it becomes part of the thread delayed free
// list that is freed later by the owning heap. If the exact usable size is too small to
// contain the pointer for the delayed list, then shrink the padding (by decreasing delta)
// so it will later not trigger an overflow error in `mi_free_block`.
static void mi_padding_shrink(const mi_page_t* page, const mi_block_t* block, const size_t min_size) {
size_t bsize;
mi_padding_t pad = mi_page_decode_padding(page, block, &bsize);
if ((bsize - pad.delta) >= min_size) return;
mi_assert_internal(bsize >= min_size);
ptrdiff_t delta = (bsize - min_size);
mi_assert_internal(delta >= 0 && delta < (ptrdiff_t)bsize);
mi_padding_t* padding = (mi_padding_t*)((uint8_t*)block + bsize);
padding->delta = (uint32_t)(delta ^ page->key[1]);
}
#else
static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
UNUSED(page);
UNUSED(block);
}
static size_t mi_page_usable_size_of(const mi_page_t* page, const mi_block_t* block) {
UNUSED(block);
return mi_page_usable_block_size(page);
}
static void mi_padding_shrink(const mi_page_t* page, const mi_block_t* block, const size_t min_size) {
UNUSED(page);
UNUSED(block);
UNUSED(min_size);
}
#endif
// ------------------------------------------------------
@ -240,6 +306,14 @@ static mi_decl_noinline void mi_free_huge_block_mt(mi_segment_t* segment, mi_pag
// multi-threaded free
static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* block)
{
// The padding check may access the non-thread-owned page for the key values.
// that is safe as these are constant and the page won't be freed (as the block is not freed yet).
mi_check_padding(page, block);
mi_padding_shrink(page, block, sizeof(mi_block_t)); // for small size, ensure we can fit the delayed thread pointers without triggering overflow detection
#if (MI_DEBUG!=0)
memset(block, MI_DEBUG_FREED, mi_usable_size(block));
#endif
// huge page segments are always abandoned and can be freed immediately
mi_segment_t* const segment = _mi_page_segment(page);
if (segment->page_kind==MI_PAGE_HUGE) {
@ -247,10 +321,6 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
return;
}
// The padding check accesses the non-thread-owned page for the key values.
// that is safe as these are constant and the page won't be freed (as the block is not freed yet).
mi_check_padding(page, block);
// Try to put the block on either the page-local thread free list, or the heap delayed free list.
mi_thread_free_t tfree;
mi_thread_free_t tfreex;
@ -295,15 +365,14 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
// regular free
static inline void _mi_free_block(mi_page_t* page, bool local, mi_block_t* block)
{
#if (MI_DEBUG)
memset(block, MI_DEBUG_FREED, mi_page_block_size(page) - MI_PADDING_SIZE);
#endif
// and push it on the free list
if (mi_likely(local)) {
// owning thread can free a block directly
if (mi_unlikely(mi_check_is_double_free(page, block))) return;
mi_check_padding(page, block);
#if (MI_DEBUG!=0)
memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
#endif
mi_block_set_next(page, block, page->local_free);
page->local_free = block;
page->used--;
@ -312,7 +381,7 @@ static inline void _mi_free_block(mi_page_t* page, bool local, mi_block_t* block
}
else if (mi_unlikely(mi_page_is_in_full(page))) {
_mi_page_unfull(page);
}
}
}
else {
_mi_free_block_mt(page,block);
@ -366,6 +435,7 @@ void mi_free(void* p) mi_attr_noexcept
const uintptr_t tid = _mi_thread_id();
mi_page_t* const page = _mi_segment_page_of(segment, p);
mi_block_t* const block = (mi_block_t*)p;
#if (MI_STAT>1)
mi_heap_t* const heap = mi_heap_get_default();
@ -377,16 +447,18 @@ void mi_free(void* p) mi_attr_noexcept
#endif
if (mi_likely(tid == segment->thread_id && page->flags.full_aligned == 0)) { // the thread id matches and it is not a full page, nor has aligned blocks
// local, and not full or aligned
mi_block_t* const block = (mi_block_t*)p;
// local, and not full or aligned
if (mi_unlikely(mi_check_is_double_free(page,block))) return;
mi_check_padding(page, block);
#if (MI_DEBUG!=0)
memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
#endif
mi_block_set_next(page, block, page->local_free);
page->local_free = block;
page->used--;
if (mi_unlikely(mi_page_all_free(page))) {
_mi_page_retire(page);
}
}
}
else {
// non-local, aligned blocks, or a full page; use the more generic path
@ -422,9 +494,10 @@ size_t mi_usable_size(const void* p) mi_attr_noexcept {
if (p==NULL) return 0;
const mi_segment_t* const segment = _mi_ptr_segment(p);
const mi_page_t* const page = _mi_segment_page_of(segment, p);
const size_t size = mi_page_usable_block_size(page);
const mi_block_t* const block = (const mi_block_t*)p;
const size_t size = mi_page_usable_size_of(page, block);
if (mi_unlikely(mi_page_has_aligned(page))) {
ptrdiff_t adjust = (uint8_t*)p - (uint8_t*)_mi_page_ptr_unalign(segment,page,p);
ptrdiff_t const adjust = (uint8_t*)p - (uint8_t*)_mi_page_ptr_unalign(segment,page,p);
mi_assert_internal(adjust >= 0 && (size_t)adjust <= size);
return (size - adjust);
}

10
src/init.c
View file

@ -31,8 +31,14 @@ const mi_page_t _mi_page_empty = {
};
#define MI_PAGE_EMPTY() ((mi_page_t*)&_mi_page_empty)
#define MI_SMALL_PAGES_EMPTY \
{ MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY(), MI_PAGE_EMPTY() }
#if defined(MI_PADDING) && (MI_INTPTR_SIZE >= 8)
#define MI_SMALL_PAGES_EMPTY { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY(), MI_PAGE_EMPTY() }
#elif defined(MI_PADDING)
#define MI_SMALL_PAGES_EMPTY { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY(), MI_PAGE_EMPTY(), MI_PAGE_EMPTY() }
#else
#define MI_SMALL_PAGES_EMPTY { MI_INIT128(MI_PAGE_EMPTY), MI_PAGE_EMPTY() }
#endif
// Empty page queues for every bin