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LibJS: Instrument HeapBlock cell allocation for ASAN

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Mark the entirety of a heap block's storage poisoned at construction.
Unpoison all of a Cell's memory before allocating it, and re-poison as
much as possible on deallocation. Unfortunately, the entirety of the
FreelistEntry must be kept unpoisoned in order for reallocation to work
correctly.

Decreasing the size of FreelistEntry or adding a larger redzone to Cells
would make the instrumentation even better.
This commit is contained in:
Andrew Kaster 2021-05-29 06:36:18 -06:00 • committed by Linus Groh
parent 81a5dcde84
commit 6aba64b60f
2 changed files with 31 additions and 4 deletions
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17
Userland/Libraries/LibJS/Heap/HeapBlock.cpp
View file

@ -6,11 +6,16 @@
#include <AK/Assertions.h>
#include <AK/NonnullOwnPtr.h>
#include <AK/Platform.h>
#include <LibJS/Heap/Heap.h>
#include <LibJS/Heap/HeapBlock.h>
#include <stdio.h>
#include <sys/mman.h>
#ifdef HAS_ADDRESS_SANITIZER
# include <sanitizer/asan_interface.h>
#endif
namespace JS {
NonnullOwnPtr<HeapBlock> HeapBlock::create_with_cell_size(Heap& heap, size_t cell_size)
@ -27,6 +32,7 @@ HeapBlock::HeapBlock(Heap& heap, size_t cell_size)
, m_cell_size(cell_size)
{
VERIFY(cell_size >= sizeof(FreelistEntry));
ASAN_POISON_MEMORY_REGION(m_storage, block_size);
}
void HeapBlock::deallocate(Cell* cell)
@ -35,11 +41,22 @@ void HeapBlock::deallocate(Cell* cell)
VERIFY(!m_freelist || is_valid_cell_pointer(m_freelist));
VERIFY(cell->state() == Cell::State::Live);
VERIFY(!cell->is_marked());
cell->~Cell();
auto* freelist_entry = new (cell) FreelistEntry();
freelist_entry->set_state(Cell::State::Dead);
freelist_entry->next = m_freelist;
m_freelist = freelist_entry;
#ifdef HAS_ADDRESS_SANITIZER
auto dword_after_freelist = round_up_to_power_of_two(reinterpret_cast<uintptr_t>(freelist_entry) + sizeof(FreelistEntry), 8);
VERIFY((dword_after_freelist - reinterpret_cast<uintptr_t>(freelist_entry)) <= m_cell_size);
VERIFY(m_cell_size >= sizeof(FreelistEntry));
// We can't poision the cell tracking data, nor the FreeListEntry's vtable or next pointer
// This means there's sizeof(FreelistEntry) data at the front of each cell that is always read/write
// On x86_64, this ends up being 24 bytes due to the size of the FreeListEntry's vtable, while on x86, it's only 12 bytes.
ASAN_POISON_MEMORY_REGION(reinterpret_cast<void*>(dword_after_freelist), m_cell_size - sizeof(FreelistEntry));
#endif
}
}