linux-kernel - Re: [PATCH] rust: types: add FOREIGN

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Message-ID: <87ecvqzhcr.fsf@kernel.org>
Date: Wed, 11 Jun 2025 12:45:56 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Danilo Krummrich" <dakr@...nel.org>,  "Miguel Ojeda"
 <ojeda@...nel.org>,  "Alex Gaynor" <alex.gaynor@...il.com>,  "Boqun Feng"
 <boqun.feng@...il.com>,  "Gary Guo" <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno Lossin" <lossin@...nel.org>,  "Trevor
 Gross" <tmgross@...ch.edu>,  "Bjorn Helgaas" <bhelgaas@...gle.com>,
  Krzysztof Wilczyński <kwilczynski@...nel.org>,  "Greg
 Kroah-Hartman"
 <gregkh@...uxfoundation.org>,  "Rafael J. Wysocki" <rafael@...nel.org>,
  "Tamir Duberstein" <tamird@...il.com>,  "Viresh Kumar"
 <viresh.kumar@...aro.org>,  <rust-for-linux@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>,  <linux-pci@...r.kernel.org>,
  Maíra
 Canal <mcanal@...lia.com>
Subject: Re: [PATCH] rust: types: add FOREIGN_ALIGN to ForeignOwnable

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> On Thu, Jun 5, 2025 at 10:00 PM Andreas Hindborg <a.hindborg@...nel.org> 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@...gle.com>
>> Suggested-by: Maíra Canal <mcanal@...lia.com>
>> Link: https://lore.kernel.org/r/20240309235927.168915-3-mcanal@igalia.com
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>
> One nit below. With that and things other folks mentioned fixed, you may add:
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>
>> 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
>> +/// integer multiple of [`Self::FOREIGN_ALIGN`].
>
> We should require non-null:

What is your rationale for this?

Best regards,
Andreas Hindborg