On Sun, Feb 16, 2025 at 8:39 PM Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
>
> On 07.02.25 14:58, Tamir Duberstein wrote:
> > Allow implementors to specify the foreign pointer type; this exposes
> > information about the pointed-to type such as its alignment.
> >
> > This requires the trait to be `unsafe` since it is now possible for
> > implementors to break soundness by returning a misaligned pointer.
> >
> > Encoding the pointer type in the trait (and avoiding pointer casts)
> > allows the compiler to check that implementors return the correct
> > pointer type. This is preferable to directly encoding the alignment in
> > the trait using a constant as the compiler would be unable to check it.
> >
> > Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > Reviewed-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> > Reviewed-by: Fiona Behrens <me@xxxxxxxxxx>
> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
> > ---
> > rust/kernel/alloc/kbox.rs | 38 ++++++++++++++++++++------------------
> > rust/kernel/miscdevice.rs | 7 ++++++-
> > rust/kernel/pci.rs | 2 ++
> > rust/kernel/platform.rs | 2 ++
> > rust/kernel/sync/arc.rs | 21 ++++++++++++---------
> > rust/kernel/types.rs | 46 +++++++++++++++++++++++++++++++---------------
> > 6 files changed, 73 insertions(+), 43 deletions(-)
>
> When compiling this (on top of rust-next), I get the following error:
>
> error[E0308]: mismatched types
> --> rust/kernel/miscdevice.rs:300:62
> |
> 300 | let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
> | ---------------------------------- ^^^^^^^ expected `*mut <<T as MiscDevice>::Ptr as ForeignOwnable>::PointedTo`, found `*mut c_void`
> | |
> | arguments to this function are incorrect
> |
> = note: expected raw pointer `*mut <<T as MiscDevice>::Ptr as ForeignOwnable>::PointedTo`
> found raw pointer `*mut c_void`
> = help: consider constraining the associated type `<<T as MiscDevice>::Ptr as ForeignOwnable>::PointedTo` to `c_void` or calling a method that returns `<<T as MiscDevice>::Ptr as ForeignOwnable>::PointedTo`
> = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
> note: associated function defined here
> --> rust/kernel/types.rs:98:15
> |
> 98 | unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> Self::Borrowed<'a>;
> | ^^^^^^
>
> error: aborting due to 1 previous error
>
> Can anyone reproduce?
>
> ---
> Cheers,
> Benno
>
Looks like this code is behind #[cfg(CONFIG_COMPAT)] and I missed
updating it. It is fixed by
diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index f1a081dd64c7..004dc87f441f 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -296,6 +296,7 @@ impl<T: MiscDevice> VtableHelper<T> {
) -> c_long {
// SAFETY: The compat ioctl call of a file can access the private data.
let private = unsafe { (*file).private_data };
+ let private = private.cast();
// SAFETY: Ioctl calls can borrow the private data of the file.
let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
I'll include that in the next version.
