8000 WIP: Add Valgrind "max address space" option. · micropython/micropython@e273f6d · GitHub
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WIP: Add Valgrind "max address space" option.
This option prevents the Python heap from reusing freed memory addresses for new allocations (obviously only viable for some workloads!) Advantage is that valgrind will be able to catch any use-after-free, that might have been missed if the freed memory address was reallocated for another use. This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton <angus@redyak.com.au>
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‎py/gc.c

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@@ -649,9 +649,11 @@ void gc_collect_end(void) {
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#if MICROPY_GC_SPLIT_HEAP
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MP_STATE_MEM(gc_last_free_area) = &MP_STATE_MEM(area);
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#endif
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#if !MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE
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for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
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area->gc_last_free_atb_index = 0;
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}
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#endif
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MP_STATE_THREAD(gc_lock_depth)--;
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GC_EXIT();
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}
@@ -838,6 +840,9 @@ void *gc_alloc(size_t n_bytes, unsigned int alloc_flags) {
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#endif
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area->gc_last_free_atb_index = (i + 1) / BLOCKS_PER_ATB;
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}
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#if MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE
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area->gc_last_free_atb_index = (i + 1) / BLOCKS_PER_ATB;
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#endif
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area->gc_last_used_block = MAX(area->gc_last_used_block, end_block);
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@@ -966,10 +971,12 @@ void gc_free(void *ptr) {
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}
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#endif
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#if !MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE
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// set the last_free pointer to this block if it's earlier in the heap
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if (block / BLOCKS_PER_ATB < area->gc_last_free_atb_index) {
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area->gc_last_free_atb_index = block / BLOCKS_PER_ATB;
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}
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#endif
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// free head and all of its tail blocks
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do {
@@ -1133,10 +1140,12 @@ void *gc_realloc(void *ptr_in, size_t n_bytes, bool allow_move) {
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}
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#endif
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#if !MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE
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// set the last_free pointer to end of this block if it's earlier in the heap
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if ((block + new_blocks) / BLOCKS_PER_ATB < area->gc_last_free_atb_index) {
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area->gc_last_free_atb_index = (block + new_blocks) / BLOCKS_PER_ATB;
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}
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#endif
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VALGRIND_MP_RESIZE_BLOCK(ptr, n_blocks, n_bytes);
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‎py/mpconfig.h

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@@ -540,6 +540,12 @@
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#define MICROPY_DEBUG_VALGRIND (0)
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#endif
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// Whether valgrind should always use new memory addresses for allocations,
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// making it easier to find use-after-free bugs.
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#ifndef MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE
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#define MICROPY_DEBUG_VALGRIND_MAX_ADDRSPACE (MICROPY_DEBUG_VALGRIND)
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#endif
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/*****************************************************************************/
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/* Optimisations */
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