From 49ceae68a0df9a92617a61e9ce8a0efcf6419585 Mon Sep 17 00:00:00 2001 From: Laine Taffin Altman Date: Wed, 3 Apr 2024 14:06:59 -0700 Subject: [PATCH] rust: init: remove impl Zeroable for Infallible 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 `Box::::init(kernel::init::zeroed())`. Thus, remove the implementation of `Zeroable` for `Infallible`, thereby avoiding the unsoundness (potential for future UB). Cc: stable@vger.kernel.org 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 Reviewed-by: Alice Ryhl Reviewed-by: Boqun Feng Reviewed-by: Benno Lossin Link: https://lore.kernel.org/r/CA160A4E-561E-4918-837E-3DCEBA74F808@me.com [ Reformatted the comment slightly. ] Signed-off-by: Miguel Ojeda --- rust/kernel/init.rs | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs index 424257284d16..09004b56fb65 100644 --- a/rust/kernel/init.rs +++ b/rust/kernel/init.rs @@ -1292,8 +1292,15 @@ impl_zeroable! { i8, i16, i32, i64, i128, isize, f32, f64, - // SAFETY: These are ZSTs, there is nothing to zero. - {} PhantomData, core::marker::PhantomPinned, Infallible, (), + // Note: do not add uninhabited types (such as `!` or `core::convert::Infallible`) to this list; + // creating an instance of an uninhabited type is immediate undefined behavior. For more on + // uninhabited/empty types, consult The Rustonomicon: + // . The Rust Reference + // also has information on undefined behavior: + // . + // + // SAFETY: These are inhabited ZSTs; there is nothing to zero and a valid value exists. + {} PhantomData, core::marker::PhantomPinned, (), // SAFETY: Type is allowed to take any value, including all zeros. {} MaybeUninit,