uefi: Wrap AtaPassThruProtocol in UnsafeCell #1782
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The existing code had some potential UB; it created a mutable pointer from a const reference and passed it across the FFI boundary. (Whether the pointee is actually mutated depends on the firmware implementation.) An `UnsafeCell` allows the interior data to be mutated through a const reference. `AtaPassThru` now contains an `UnsafeCell<AtaPassThruProtocol>`, which allows a mutable pointer to be created with less risk of UB. (Note that it's still not allowed to create multiple mutable _references_ to the data, but as long as only raw pointers are used, it should be OK.) The `AtaDevice` and `AtaDeviceIterator` types have been adjusted to take a reference to the `UnsafeCell`.
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The existing code had some potential UB; it created a mutable pointer from a const reference and passed it across the FFI boundary. (Whether the pointee is actually mutated depends on the firmware implementation.)
An
UnsafeCellallows the interior data to be mutated through a const reference.AtaPassThrunow contains anUnsafeCell<AtaPassThruProtocol>, which allows a mutable pointer to be created with less risk of UB. (Note that it's still not allowed to create multiple mutable references to the data, but as long as only raw pointers are used, it should be OK.)The
AtaDeviceandAtaDeviceIteratortypes have been adjusted to take a reference to theUnsafeCell.Note: we'll likely want the same change in the nvme and scsi protocols.
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