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

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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
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2
Userland/Libraries/LibJS/Heap/HeapBlock.cpp
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@ -26,7 +26,7 @@ NonnullOwnPtr<HeapBlock> HeapBlock::create_with_cell_size(Heap& heap, CellAlloca
#else
char const* name = nullptr;
#endif
auto* block = static_cast<HeapBlock*>(heap.block_allocator().allocate_block(name));
auto* block = static_cast<HeapBlock*>(cell_allocator.block_allocator().allocate_block(name));
new (block) HeapBlock(heap, cell_allocator, cell_size);
return NonnullOwnPtr<HeapBlock>(NonnullOwnPtr<HeapBlock>::Adopt, *block);
}