Messages in this thread | | | Date | Thu, 18 Apr 2024 16:23:06 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v6 3/4] rust: uaccess: add typed accessors for userspace pointers |
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On 18.04.24 15:17, Alice Ryhl wrote: > On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <benno.lossin@protonme> wrote: >> >> On 18.04.24 10:59, Alice Ryhl wrote: >>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs >>> index 8fad61268465..9c57c6c75553 100644 >>> --- a/rust/kernel/types.rs >>> +++ b/rust/kernel/types.rs >>> @@ -409,3 +409,67 @@ pub enum Either<L, R> { >>> /// Constructs an instance of [`Either`] containing a value of type `R`. >>> Right(R), >>> } >>> + >>> +/// Types for which any bit pattern is valid. >>> +/// >>> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so >>> +/// reading arbitrary bytes into something that contains a `bool` is not okay. >>> +/// >>> +/// It's okay for the type to have padding, as initializing those bytes has no effect. >>> +/// >>> +/// # Safety >>> +/// >>> +/// All bit-patterns must be valid for this type. This type must not have interior mutability. >> >> What is the reason for disallowing interior mutability here? I agree >> that it is necessary for `AsBytes`, but I don't think we need it here. >> For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also >> should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>` >> already fails the "All bit-patterns must be valid for this type". > > If T: FromBytes allows transmuting &[u8; size_of::<T>] into &T, then > it would be a problem as you could then use it to modify the original > &[u8].
Ahh that makes a lot of sense.
-- Cheers, Benno
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