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improve encoding of padding canary and buffer overflow detection

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This commit is contained in:
daan 2020-02-01 12:15:12 -08:00
parent 40f1e1e07b
commit aa68b8cbc7
6 changed files with 78 additions and 66 deletions
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33
include/mimalloc-internal.h
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@ -519,30 +519,37 @@ static inline uintptr_t mi_rotr(uintptr_t x, uintptr_t shift) {
return ((x >> shift) | (x << (MI_INTPTR_BITS - shift)));
}
static inline mi_block_t* mi_block_nextx( const void* null, const mi_block_t* block, uintptr_t key1, uintptr_t key2 ) {
static inline void* mi_ptr_decode(const void* null, const mi_encoded_t x, const uintptr_t* keys) {
void* p = (void*)(mi_rotr(x - keys[0], keys[0]) ^ keys[1]);
return (mi_unlikely(p==null) ? NULL : p);
}
static inline mi_encoded_t mi_ptr_encode(const void* null, const void* p, const uintptr_t* keys) {
uintptr_t x = (uintptr_t)(mi_unlikely(p==NULL) ? null : p);
return mi_rotl(x ^ keys[1], keys[0]) + keys[0];
}
static inline mi_block_t* mi_block_nextx( const void* null, const mi_block_t* block, const uintptr_t* keys ) {
#ifdef MI_ENCODE_FREELIST
mi_block_t* b = (mi_block_t*)(mi_rotr(block->next - key1, key1) ^ key2);
if (mi_unlikely((void*)b==null)) { b = NULL; }
return b;
return (mi_block_t*)mi_ptr_decode(null, block->next, keys);
#else
UNUSED(key1); UNUSED(key2); UNUSED(null);
UNUSED(keys); UNUSED(null);
return (mi_block_t*)block->next;
#endif
}
static inline void mi_block_set_nextx(const void* null, mi_block_t* block, const mi_block_t* next, uintptr_t key1, uintptr_t key2) {
static inline void mi_block_set_nextx(const void* null, mi_block_t* block, const mi_block_t* next, const uintptr_t* keys) {
#ifdef MI_ENCODE_FREELIST
if (mi_unlikely(next==NULL)) { next = (mi_block_t*)null; }
block->next = mi_rotl((uintptr_t)next ^ key2, key1) + key1;
block->next = mi_ptr_encode(null, next, keys);
#else
UNUSED(key1); UNUSED(key2); UNUSED(null);
UNUSED(keys); UNUSED(null);
block->next = (mi_encoded_t)next;
#endif
}
static inline mi_block_t* mi_block_next(const mi_page_t* page, const mi_block_t* block) {
#ifdef MI_ENCODE_FREELIST
mi_block_t* next = mi_block_nextx(page,block,page->key[0],page->key[1]);
mi_block_t* next = mi_block_nextx(page,block,page->keys);
// check for free list corruption: is `next` at least in the same page?
// TODO: check if `next` is `page->block_size` aligned?
if (mi_unlikely(next!=NULL && !mi_is_in_same_page(block, next))) {
@ -552,16 +559,16 @@ static inline mi_block_t* mi_block_next(const mi_page_t* page, const mi_block_t*
return next;
#else
UNUSED(page);
return mi_block_nextx(page,block,0,0);
return mi_block_nextx(page,block,NULL);
#endif
}
static inline void mi_block_set_next(const mi_page_t* page, mi_block_t* block, const mi_block_t* next) {
#ifdef MI_ENCODE_FREELIST
mi_block_set_nextx(page,block,next, page->key[0], page->key[1]);
mi_block_set_nextx(page,block,next, page->keys);
#else
UNUSED(page);
mi_block_set_nextx(page,block, next,0,0);
mi_block_set_nextx(page,block,next,NULL);
#endif
}

25
include/mimalloc-types.h
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@ -48,25 +48,24 @@ terms of the MIT license. A copy of the license can be found in the file
#endif
#endif
// Reserve extra padding at the end of each block to be more resilient against heap block overflows.
// The padding can detect byte-precise buffer overflow on free.
#if !defined(MI_PADDING) && (MI_DEBUG>=1)
#define MI_PADDING 1
#endif
// Encoded free lists allow detection of corrupted free lists
// and can detect buffer overflows, modify after free, and double `free`s.
#if (MI_SECURE>=3 || MI_DEBUG>=1)
#if (MI_SECURE>=3 || MI_DEBUG>=1 || defined(MI_PADDING))
#define MI_ENCODE_FREELIST 1
#endif
// Reserve extra padding at the end of each block to be more resilient against heap block overflows.
// If free lists are encoded, the padding can detect byte-precise buffer overflow on free.
#if (!defined(MI_PADDING) && (MI_SECURE>=3 || MI_DEBUG>=1))
#define MI_PADDING
#endif
// ------------------------------------------------------
// Platform specific values
// ------------------------------------------------------
// ------------------------------------------------------
// Size of a pointer.
// We assume that `sizeof(void*)==sizeof(intptr_t)`
@ -218,7 +217,7 @@ typedef struct mi_page_s {
mi_block_t* free; // list of available free blocks (`malloc` allocates from this list)
#ifdef MI_ENCODE_FREELIST
uintptr_t key[2]; // two random keys to encode the free lists (see `_mi_block_next`)
uintptr_t keys[2]; // two random keys to encode the free lists (see `_mi_block_next`)
#endif
uint32_t used; // number of blocks in use (including blocks in `local_free` and `thread_free`)
uint32_t xblock_size; // size available in each block (always `>0`)
@ -306,8 +305,8 @@ typedef struct mi_random_cxt_s {
// In debug mode there is a padding stucture at the end of the blocks to check for buffer overflows
#if defined(MI_PADDING)
typedef struct mi_padding_s {
uint32_t block; // (encoded) lower 32 bits of the block address. (to check validity of the block)
uint32_t delta; // (encoded) padding bytes before the block. (mi_usable_size(p) - decode(delta) == exact allocated bytes)
uint32_t canary; // encoded block value to check validity of the padding (in case of overflow)
uint32_t delta; // padding bytes before the block. (mi_usable_size(p) - delta == exact allocated bytes)
} mi_padding_t;
#define MI_PADDING_SIZE (sizeof(mi_padding_t))
#define MI_PADDING_WSIZE ((MI_PADDING_SIZE + MI_INTPTR_SIZE - 1) / MI_INTPTR_SIZE)
@ -327,7 +326,7 @@ struct mi_heap_s {
volatile _Atomic(mi_block_t*) thread_delayed_free;
uintptr_t thread_id; // thread this heap belongs too
uintptr_t cookie; // random cookie to verify pointers (see `_mi_ptr_cookie`)
uintptr_t key[2]; // two random keys used to encode the `thread_delayed_free` list
uintptr_t keys[2]; // two random keys used to encode the `thread_delayed_free` list
mi_random_ctx_t random; // random number context used for secure allocation
size_t page_count; // total number of pages in the `pages` queues.
bool no_reclaim; // `true` if this heap should not reclaim abandoned pages

54
src/alloc.c
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@ -48,10 +48,11 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
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]);
padding->canary = (uint32_t)(mi_ptr_encode(page,block,page->keys));
padding->delta = (uint32_t)(delta);
uint8_t* fill = (uint8_t*)padding - delta;
for (ptrdiff_t i = 0; i < delta; i++) { fill[i] = MI_DEBUG_PADDING; }
const size_t maxpad = (delta > MI_MAX_ALIGN_SIZE ? MI_MAX_ALIGN_SIZE : delta); // set at most N initial padding bytes
for (size_t i = 0; i < maxpad; i++) { fill[i] = MI_DEBUG_PADDING; }
#endif
return block;
}
@ -175,7 +176,7 @@ static mi_decl_noinline bool mi_check_is_double_freex(const mi_page_t* page, con
}
static inline bool mi_check_is_double_free(const mi_page_t* page, const mi_block_t* block) {
mi_block_t* n = mi_block_nextx(page, block, page->key[0], page->key[1]); // pretend it is freed, and get the decoded first field
mi_block_t* n = mi_block_nextx(page, block, page->keys); // pretend it is freed, and get the decoded first field
if (((uintptr_t)n & (MI_INTPTR_SIZE-1))==0 && // quick check: aligned pointer?
(n==NULL || mi_is_in_same_page(block, n))) // quick check: in same page or NULL?
{
@ -198,33 +199,35 @@ static inline bool mi_check_is_double_free(const mi_page_t* page, const mi_block
// ---------------------------------------------------------------------------
#if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
static mi_padding_t mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* bsize) {
static bool mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* delta, 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;
*delta = padding->delta;
return ((uint32_t)mi_ptr_encode(page,block,page->keys) == padding->canary && *delta <= *bsize);
}
// 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;
size_t delta;
bool ok = mi_page_decode_padding(page, block, &delta, &bsize);
mi_assert_internal(ok); mi_assert_internal(delta <= bsize);
return (ok ? bsize - delta : 0);
}
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_t delta;
bool ok = mi_page_decode_padding(page, block, &delta, &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 (!ok) return false;
mi_assert_internal(bsize >= delta);
*size = bsize - delta;
uint8_t* fill = (uint8_t*)block + bsize - delta;
const size_t maxpad = (delta > MI_MAX_ALIGN_SIZE ? MI_MAX_ALIGN_SIZE : delta); // check at most the first N padding bytes
for (size_t i = 0; i < maxpad; i++) {
if (fill[i] != MI_DEBUG_PADDING) {
*wrong = bsize - pad.delta + i;
*wrong = bsize - delta + i;
return false;
}
}
@ -245,13 +248,16 @@ static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
// 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;
size_t delta;
bool ok = mi_page_decode_padding(page, block, &delta, &bsize);
mi_assert_internal(ok);
if (!ok || (bsize - delta) >= min_size) return; // usually already enough space
mi_assert_internal(bsize >= min_size);
ptrdiff_t delta = (bsize - min_size);
mi_assert_internal(delta >= 0 && delta < (ptrdiff_t)bsize);
if (bsize < min_size) return; // should never happen
size_t new_delta = (bsize - min_size);
mi_assert_internal(new_delta < bsize);
mi_padding_t* padding = (mi_padding_t*)((uint8_t*)block + bsize);
padding->delta = (uint32_t)(delta ^ page->key[1]);
padding->delta = (uint32_t)new_delta;
}
#else
static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
@ -348,7 +354,7 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
mi_block_t* dfree;
do {
dfree = mi_atomic_read_ptr_relaxed(mi_block_t,&heap->thread_delayed_free);
mi_block_set_nextx(heap,block,dfree, heap->key[0], heap->key[1]);
mi_block_set_nextx(heap,block,dfree, heap->keys);
} while (!mi_atomic_cas_ptr_weak(mi_block_t,&heap->thread_delayed_free, block, dfree));
}

4
src/heap.c
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@ -195,8 +195,8 @@ mi_heap_t* mi_heap_new(void) {
heap->thread_id = _mi_thread_id();
_mi_random_split(&bheap->random, &heap->random);
heap->cookie = _mi_heap_random_next(heap) | 1;
heap->key[0] = _mi_heap_random_next(heap);
heap->key[1] = _mi_heap_random_next(heap);
heap->keys[0] = _mi_heap_random_next(heap);
heap->keys[1] = _mi_heap_random_next(heap);
heap->no_reclaim = true; // don't reclaim abandoned pages or otherwise destroy is unsafe
return heap;
}

8
src/init.c
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@ -174,8 +174,8 @@ static bool _mi_heap_init(void) {
heap->thread_id = _mi_thread_id();
_mi_random_init(&heap->random);
heap->cookie = _mi_heap_random_next(heap) | 1;
heap->key[0] = _mi_heap_random_next(heap);
heap->key[1] = _mi_heap_random_next(heap);
heap->keys[0] = _mi_heap_random_next(heap);
heap->keys[1] = _mi_heap_random_next(heap);
heap->tld = tld;
tld->heap_backing = heap;
tld->segments.stats = &tld->stats;
@ -419,8 +419,8 @@ void mi_process_init(void) mi_attr_noexcept {
_mi_random_init(&_mi_heap_main.random);
#ifndef __APPLE__ // TODO: fix this? cannot update cookie if allocation already happened..
_mi_heap_main.cookie = _mi_heap_random_next(&_mi_heap_main);
_mi_heap_main.key[0] = _mi_heap_random_next(&_mi_heap_main);
_mi_heap_main.key[1] = _mi_heap_random_next(&_mi_heap_main);
_mi_heap_main.keys[0] = _mi_heap_random_next(&_mi_heap_main);
_mi_heap_main.keys[1] = _mi_heap_random_next(&_mi_heap_main);
#endif
mi_process_setup_auto_thread_done();
_mi_os_init();

14
src/page.c
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@ -281,7 +281,7 @@ void _mi_heap_delayed_free(mi_heap_t* heap) {
// and free them all
while(block != NULL) {
mi_block_t* next = mi_block_nextx(heap,block, heap->key[0], heap->key[1]);
mi_block_t* next = mi_block_nextx(heap,block, heap->keys);
// use internal free instead of regular one to keep stats etc correct
if (!_mi_free_delayed_block(block)) {
// we might already start delayed freeing while another thread has not yet
@ -289,7 +289,7 @@ void _mi_heap_delayed_free(mi_heap_t* heap) {
mi_block_t* dfree;
do {
dfree = mi_atomic_read_ptr_relaxed(mi_block_t,&heap->thread_delayed_free);
mi_block_set_nextx(heap, block, dfree, heap->key[0], heap->key[1]);
mi_block_set_nextx(heap, block, dfree, heap->keys);
} while (!mi_atomic_cas_ptr_weak(mi_block_t,&heap->thread_delayed_free, block, dfree));
}
block = next;
@ -348,7 +348,7 @@ void _mi_page_abandon(mi_page_t* page, mi_page_queue_t* pq) {
#if MI_DEBUG>1
// check there are no references left..
for (mi_block_t* block = (mi_block_t*)pheap->thread_delayed_free; block != NULL; block = mi_block_nextx(pheap, block, pheap->key[0], pheap->key[1])) {
for (mi_block_t* block = (mi_block_t*)pheap->thread_delayed_free; block != NULL; block = mi_block_nextx(pheap, block, pheap->keys)) {
mi_assert_internal(_mi_ptr_page(block) != page);
}
#endif
@ -609,8 +609,8 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi
mi_assert_internal(page_size / block_size < (1L<<16));
page->reserved = (uint16_t)(page_size / block_size);
#ifdef MI_ENCODE_FREELIST
page->key[0] = _mi_heap_random_next(heap);
page->key[1] = _mi_heap_random_next(heap);
page->keys[0] = _mi_heap_random_next(heap);
page->keys[1] = _mi_heap_random_next(heap);
#endif
page->is_zero = page->is_zero_init;
@ -623,8 +623,8 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi
mi_assert_internal(page->retire_expire == 0);
mi_assert_internal(!mi_page_has_aligned(page));
#if (MI_ENCODE_FREELIST)
mi_assert_internal(page->key[0] != 0);
mi_assert_internal(page->key[1] != 0);
mi_assert_internal(page->keys[0] != 0);
mi_assert_internal(page->keys[1] != 0);
#endif
mi_assert_expensive(mi_page_is_valid_init(page));