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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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3
include/mimalloc-internal.h
View file

@ -377,7 +377,8 @@ static inline size_t mi_page_block_size(const mi_page_t* page) {
}
}
// Get the client usable block size of a page (without padding etc)
// Get the usable block size of a page without fixed padding.
// This may still include internal padding due to alignment and rounding up size classes.
static inline size_t mi_page_usable_block_size(const mi_page_t* page) {
return mi_page_block_size(page) - MI_PADDING_SIZE;
}

30
include/mimalloc-types.h
View file

@ -49,23 +49,17 @@ terms of the MIT license. A copy of the license can be found in the file
#endif
// Encoded free lists allow detection of corrupted free lists
// and can detect buffer overflows and double `free`s.
// and can detect buffer overflows, modify after free, and double `free`s.
#if (MI_SECURE>=3 || MI_DEBUG>=1)
#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 is checked if it was modified on free.
// 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
// The padding size must be at least `sizeof(intptr_t)`!
#if defined(MI_PADDING)
#define MI_PADDING_WSIZE 1
#else
#define MI_PADDING_WSIZE 0
#endif
// ------------------------------------------------------
@ -95,7 +89,6 @@ terms of the MIT license. A copy of the license can be found in the file
#define MI_INTPTR_SIZE (1<<MI_INTPTR_SHIFT)
#define MI_INTPTR_BITS (MI_INTPTR_SIZE*8)
#define MI_PADDING_SIZE (MI_PADDING_WSIZE * MI_INTPTR_SIZE)
#define KiB ((size_t)1024)
#define MiB (KiB*KiB)
@ -309,7 +302,22 @@ typedef struct mi_random_cxt_s {
int output_available;
} mi_random_ctx_t;
#define MI_PAGES_DIRECT (MI_SMALL_WSIZE_MAX + MI_PADDING_WSIZE + 1)
// 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)
} 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)
#else
#define MI_PADDING_SIZE 0
#define MI_PADDING_WSIZE 0
#endif
#define MI_PAGES_DIRECT (MI_SMALL_WSIZE_MAX + MI_PADDING_WSIZE + 1)
// A heap owns a set of pages.
struct mi_heap_s {
@ -333,7 +341,7 @@ struct mi_heap_s {
#define MI_DEBUG_UNINIT (0xD0)
#define MI_DEBUG_FREED (0xDF)
#define MI_DEBUG_PADDING (0xDE)
#if (MI_DEBUG)
// use our own assertion to print without memory allocation