Fix unsoundness in our representation of the MADT#223
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IsaacWoods merged 2 commits intorust-osdev:mainfrom Jan 30, 2025
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Fix unsoundness in our representation of the MADT#223IsaacWoods merged 2 commits intorust-osdev:mainfrom
IsaacWoods merged 2 commits intorust-osdev:mainfrom
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This prevents an `Madt` being moved away from its following, but not represented, dynamic entries. This would previously have caused unsoundness as arbitrary memory would be read from after wherever the `Madt` had ended up. By prevening the user from getting anything other than a `Pin<&Madt>`, this is prevented.
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- Adapted to the changes introduced in the acpi crate PR #223, specifically for the MADT structure. - Updated handling of MADT entries to align with the new API. - Used Pin<&Madt> to ensure immovable references when accessing MADT entries, in response to changes in the MADT structure. - Adjusted usage of MADT pointers to accommodate the new access pattern introduced by the acpi crate update. See: rust-osdev/acpi#223
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As reported in #218, we had a glaring soundness hole in the way we represented the MADT, which allowed an
Madtto be moved away from its following entries. WhenMadt::entrieswas called, this would lead to arbitrary memory being read from after wherever theMadtended up.Moving the structures representing the tables is unlikely if the library is used as intended (and structures were
Copyonly because this was required byrepr(packed), but this is not actually required in the case ofMadt), but this should obviously still be closed.We make this sound by making
Madt: !Unpin, which prevents the structure from being moved if in aPin. To minimise difficulty usingPhysicalMapping, we continue to allow mappings to deref to normal references if the underlyingT: Unpin, but only allow access throughPin<&T>ifT: !Unpin(ideally we'd just produce aPinthrough deref but I don't think is possible?).This feels like it should address the soundness issue from my end, but my knowledge surrounding
Pinis still dubious at times, so anyone more knowledgeable who feels this is not correct please do let me know.This would unfortunately be a breaking change.
cc @pyelias