Oops! Formatting issue; ignore this one.
Thanks,
Laine
> On Apr 1, 2024, at 6:53 PM, Laine Taffin Altman <alexanderaltman@xxxxxx> wrote:
>
> A type is inhabited if at least one valid value of that type exists; a type is uninhabited if no valid values of that type exist. The terms "inhabited" and "uninhabited" in this sense originate in type theory, a branch of mathematics.
>
> In Rust, producing an invalid value of any type is immediate undefined behavior (UB); this includes via zeroing memory. Therefore, since an uninhabited type has no valid values, producing any values at all for it is UB.
>
> The Rust standard library type `core::convert::Infallible` is uninhabited, by virtue of having been declared as an enum with no cases, which always produces uninhabited types in Rust.
>
> The current kernel code allows this UB to be triggered, for example by code like:
> `pr_info!("{}”, Box::<core::convert::Infallible>::init(kernel::init::zeroed())?);`
>
> Thus, remove the implementation of `Zeroable` for `Infallible`, thereby avoiding the UB.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function")
> Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13
> Signed-off-by: Laine Taffin Altman <alexanderaltman@xxxxxx>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> —
> V1 -> V2: Added more documentation to the comment, with links; also added more details to the commit message.
>
> rust/kernel/init.rs | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index 424257284d16..9353c9919fd4 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -1292,8 +1292,11 @@ macro_rules! impl_zeroable {
> i8, i16, i32, i64, i128, isize,
> f32, f64,
>
> - // SAFETY: These are ZSTs, there is nothing to zero.
> - {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (),
> + // SAFETY: These are inhabited ZSTs; there is nothing to zero and a valid value exists.
> + // Note: do not add uninhabited types (such as ! or Infallible) to this list; creating an instance of an uninhabited type is immediate undefined behavior.
> + // For more on uninhabited/empty types, consult The Rustonomicon: https://doc.rust-lang.org/stable/nomicon/exotic-sizes.html#empty-types
> + // The Rust Reference also has information on undefined behavior: https://doc.rust-lang.org/stable/reference/behavior-considered-undefined.html
> + {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, (),
>
> // SAFETY: Type is allowed to take any value, including all zeros.
> {<T>} MaybeUninit<T>,
> --
> 2.44.0
