The title should probably also mention that it removes `PointedTo`. On Thu Jun 5, 2025 at 9:55 PM CEST, Andreas Hindborg wrote: > The current implementation of `ForeignOwnable` is leaking the type of the > opaque pointer to consumers of the API. This allows consumers of the opaque > pointer to rely on the information that can be extracted from the pointer > type. > > To prevent this, change the API to the version suggested by Maira > Canal (link below): Remove `ForeignOwnable::PointedTo` in favor of a > constant, which specifies the alignment of the pointers returned by > `into_foreign`. > > Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > Suggested-by: Maíra Canal <mcanal@xxxxxxxxxx> > Link: https://lore.kernel.org/r/20240309235927.168915-3-mcanal@xxxxxxxxxx > Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx> A couple nits and documentation review below, with those fixed: Reviewed-by: Benno Lossin <lossin@xxxxxxxxxx> > --- > rust/kernel/alloc/kbox.rs | 40 ++++++++++++++++++++++------------------ > rust/kernel/miscdevice.rs | 10 +++++----- > rust/kernel/pci.rs | 2 +- > rust/kernel/platform.rs | 2 +- > rust/kernel/sync/arc.rs | 23 ++++++++++++----------- > rust/kernel/types.rs | 46 +++++++++++++++++++++------------------------- > rust/kernel/xarray.rs | 8 ++++---- > 7 files changed, 66 insertions(+), 65 deletions(-) > > diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs > index c386ff771d50..97f45bc4d74f 100644 > --- a/rust/kernel/alloc/kbox.rs > +++ b/rust/kernel/alloc/kbox.rs > @@ -398,70 +398,74 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E> > } > } > > -// SAFETY: The `into_foreign` function returns a pointer that is well-aligned. > +// SAFETY: The pointer returned by `into_foreign` comes from a well aligned > +// pointer to `T`. > unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A> > where > A: Allocator, > { > - type PointedTo = T; > + const FOREIGN_ALIGN: usize = core::mem::align_of::<T>(); > type Borrowed<'a> = &'a T; > type BorrowedMut<'a> = &'a mut T; > > - fn into_foreign(self) -> *mut Self::PointedTo { > - Box::into_raw(self) > + fn into_foreign(self) -> *mut crate::ffi::c_void { How about we import the prelude, then you can just write `*mut c_void` everywhere instead of having to write `crate::ffi` all the time. > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs > index c7af0aa48a0a..6603079b05af 100644 > --- a/rust/kernel/sync/arc.rs > +++ b/rust/kernel/sync/arc.rs > @@ -140,10 +140,9 @@ pub struct Arc<T: ?Sized> { > _p: PhantomData<ArcInner<T>>, > } > > -#[doc(hidden)] > #[pin_data] > #[repr(C)] > -pub struct ArcInner<T: ?Sized> { > +struct ArcInner<T: ?Sized> { I agree with this change, but let's mention it in the commit message. > refcount: Opaque<bindings::refcount_t>, > data: T, > } > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index 22985b6f6982..025c619a2195 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -21,15 +21,11 @@ > /// > /// # Safety > /// > -/// Implementers must ensure that [`into_foreign`] returns a pointer which meets the alignment > -/// requirements of [`PointedTo`]. > -/// > -/// [`into_foreign`]: Self::into_foreign > -/// [`PointedTo`]: Self::PointedTo > +/// Implementers must ensure that [`Self::into_foreign`] return pointers with alignment that is an s/return/returns/ > +/// integer multiple of [`Self::FOREIGN_ALIGN`]. I would just write "returns pointers aligned to [`Self::FOREIGN_ALIGN`]". > pub unsafe trait ForeignOwnable: Sized { > - /// Type used when the value is foreign-owned. In practical terms only defines the alignment of > - /// the pointer. > - type PointedTo; > + /// The alignment of pointers returned by `into_foreign`. > + const FOREIGN_ALIGN: usize; > > /// Type used to immutably borrow a value that is currently foreign-owned. > type Borrowed<'a>; > @@ -39,18 +35,17 @@ pub unsafe trait ForeignOwnable: Sized { > > /// Converts a Rust-owned object to a foreign-owned one. > /// > - /// # Guarantees Why remove this section? I think we should streamline it, (make it use bullet points, shorten the sentences etc). We can keep the paragraph you wrote below as normal docs. > - /// > - /// The return value is guaranteed to be well-aligned, but there are no other guarantees for > - /// this pointer. For example, it might be null, dangling, or point to uninitialized memory. > - /// Using it in any way except for [`ForeignOwnable::from_foreign`], [`ForeignOwnable::borrow`], > - /// [`ForeignOwnable::try_from_foreign`] can result in undefined behavior. > + /// The foreign representation is a pointer to void. The minimum alignment of the returned > + /// pointer is [`Self::FOREIGN_ALIGN`]. There are no other guarantees for this pointer. For > + /// example, it might be invalid, dangling or pointing to uninitialized memory. Using it in any > + /// way except for [`from_foreign`], [`try_from_foreign`], [`borrow`], or [`borrow_mut`] can > + /// result in undefined behavior. > /// > /// [`from_foreign`]: Self::from_foreign > /// [`try_from_foreign`]: Self::try_from_foreign > /// [`borrow`]: Self::borrow > /// [`borrow_mut`]: Self::borrow_mut > - fn into_foreign(self) -> *mut Self::PointedTo; > + fn into_foreign(self) -> *mut crate::ffi::c_void;
