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LibJS: Never give back virtual memory once it belongs to a cell type

Instead of returning HeapBlock memory to the kernel (or a non-type
specific shared cache), we now keep a BlockAllocator per CellAllocator
and implement "deallocation" by basically informing the kernel that we
don't need the physical memory right now.

This is done with MADV_FREE or MADV_DONTNEED if available, but for other
platforms (including SerenityOS) we munmap and then re-mmap the memory
to achieve the same effect. It's definitely clunky, so I've added a
FIXME about implementing the madvise options on SerenityOS too.

The important outcome of this change is that GC types that use a
type-specific allocator become immune to use-after-free type confusion
attacks, since their virtual addresses will only ever be re-used for
the same exact type again and again.

Fixes #22274
This commit is contained in:
Andreas Kling 2023-12-31 11:36:18 +01:00
parent bcb1e548f1
commit b6d4eea7ac
10 changed files with 47 additions and 36 deletions

View file

@ -15,7 +15,6 @@
#include <AK/Vector.h>
#include <LibCore/Forward.h>
#include <LibJS/Forward.h>
#include <LibJS/Heap/BlockAllocator.h>
#include <LibJS/Heap/Cell.h>
#include <LibJS/Heap/CellAllocator.h>
#include <LibJS/Heap/Handle.h>
@ -83,8 +82,6 @@ public:
void register_cell_allocator(Badge<CellAllocator>, CellAllocator&);
BlockAllocator& block_allocator() { return m_block_allocator; }
void uproot_cell(Cell* cell);
private:
@ -154,8 +151,6 @@ private:
Vector<GCPtr<Cell>> m_uprooted_cells;
BlockAllocator m_block_allocator;
size_t m_gc_deferrals { 0 };
bool m_should_gc_when_deferral_ends { false };