Security-harden the guest's memory allocator #726
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Extracted from #631
| @@ -4,26 +4,34 @@ | |||
| use core::alloc::{GlobalAlloc, Layout}; | |||
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| struct SimpleAllocator { | |||
| next_alloc: usize, | |||
| next_alloc: *mut u8, | |||
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This type is more truthful, and simplifies our code.
| } | ||
| core::hint::assert_unchecked(align.is_power_of_two()); | ||
| core::hint::assert_unchecked(align != 0); | ||
| heap_pos = heap_pos.add(heap_pos.align_offset(align)); |
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We use the proper Rust functions for working with pointers now. That makes both the type checker happier (when working with pointers instead of usize), and hopefully also clues in the optimiser a bit more.
But the latter would just be a welcome side effect, if it does happen.
| next_alloc: 0xFFFF_FFFF, | ||
| }; | ||
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| pub unsafe fn init_heap() { |
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We no longer need init_heap, because we can directly statically initialise to &raw mut _sheap,.
| // (We could also return a null pointer, but only malicious programs would ever hit this.) | ||
| heap_pos = heap_pos.strict_add(layout.size()); |
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Alas, ptr type doesn't have strict_add, but add does nearly the same.
matthiasgoergens
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matthiasgoergens
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Here we harden the security of the guest's memory allocator: we no longer rely on manual initialisation code for its proper operation.
Because we remove code, it also simplifies the allocator. Hopefully making it easier to understand.
Extracted from #631