Hi Benno, "Benno Lossin" <lossin@xxxxxxxxxx> writes: > 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. OK. > >> 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. Right. > >> 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/ Thanks. > >> +/// integer multiple of [`Self::FOREIGN_ALIGN`]. > > I would just write "returns pointers aligned to [`Self::FOREIGN_ALIGN`]". OK. > >> 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. Not sure exactly what you are going for here. How is this: Converts a Rust-owned object to a foreign-owned one. The foreign representation is a pointer to void. # Guarantees - Minimum alignment of 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. Best regards, Andreas Hindborg
