From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E2AD22172F; Tue, 10 Jun 2025 09:27:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749547659; cv=none; b=Sz0WhbDEeWLop5rKMAgPQ9OoourymyeW4b90plTsg+Q3VFAM+SyoIJdgiglDfgq29AsJXyZmbT7eMGbZw8rcZbCOf7rap/GSQf8Oz4zXhyp+NJUDIslrKz7mfBqUmb1xbUwtFSnie4DqEC4GRWibmGLH5IuGYCxBqVV0qf7FSrk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749547659; c=relaxed/simple; bh=ZqzZXwBienY7zE2X7UrzBwvmMt1YWhqjZH4WMRWX/Zo=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=S646/lJgC+sURd8Lm+6OvVwm4n3MzCf1LvM8FAWLnumnhDZkYCUnt0235Gh9of4Kr73fPkZVo5ZMa2NyyKKdONfOth2tbQ+FoFnQPcTmynr+o+oRCNKYWhu8st7sZwKLFcPjDxeARaLLueGZ85tstsshWEd3D0QrIX7AyTB4o/g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AyRXYHiW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AyRXYHiW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 630E1C4CEED; Tue, 10 Jun 2025 09:27:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749547659; bh=ZqzZXwBienY7zE2X7UrzBwvmMt1YWhqjZH4WMRWX/Zo=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=AyRXYHiWAEcp+X0pY5kz+1POSUUq2ems/XitGiLQs2i7z1GICUOyZzcPKeEYJOFfi XPYiIQXtSWVXOBNHDRewq1DowMlebBIJCeOYo8RJf2yHWhCtS4lxvPVst6jqxQ4X+n qJEyfIDVygKPARuYxlqqOsKOA5Fnu6dn1gGposASs03Yw1yLvXmdwhTCz01qoGVnm5 e+eA26om9KAtz8ez/ultTGmP+z/F+gX0ta8mAqwOQKbU06bfjBc2o1Di/F3bd1rZtc qIUqSuJ3EmEQyJWlk5q/Gen4EDNepQplZZfF+fjlmp+5Q3rFQ011FW2hmtsTNsCY9d 6eUZtWUUzJeUA== From: Andreas Hindborg To: "Benno Lossin" Cc: "Danilo Krummrich" , "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , "Gary Guo" , =?utf-8?Q?Bj?= =?utf-8?Q?=C3=B6rn?= Roy Baron , "Alice Ryhl" , "Trevor Gross" , "Bjorn Helgaas" , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , "Greg Kroah-Hartman" , "Rafael J. Wysocki" , "Tamir Duberstein" , "Viresh Kumar" , , , , =?utf-8?Q?Ma=C3=ADra?= Canal Subject: Re: [PATCH] rust: types: add FOREIGN_ALIGN to ForeignOwnable In-Reply-To: (Benno Lossin's message of "Fri, 06 Jun 2025 10:23:21 +0200") References: <20250605-pointed-to-v1-1-ee1e262912cc@kernel.org> User-Agent: mu4e 1.12.9; emacs 30.1 Date: Tue, 10 Jun 2025 11:27:28 +0200 Message-ID: <87sek82bgf.fsf@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Benno, "Benno Lossin" 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 opa= que >> 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 >> Suggested-by: Ma=C3=ADra Canal >> Link: https://lore.kernel.org/r/20240309235927.168915-3-mcanal@igalia.com >> Signed-off-by: Andreas Hindborg > > A couple nits and documentation review below, with those fixed: > > Reviewed-by: Benno Lossin > >> --- >> 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(init: impl Init, flags: Flags= ) -> Result >> } >> } >> >> -// SAFETY: The `into_foreign` function returns a pointer that is well-a= ligned. >> +// SAFETY: The pointer returned by `into_foreign` comes from a well ali= gned >> +// pointer to `T`. >> unsafe impl ForeignOwnable for Box >> where >> A: Allocator, >> { >> - type PointedTo =3D T; >> + const FOREIGN_ALIGN: usize =3D core::mem::align_of::(); >> type Borrowed<'a> =3D &'a T; >> type BorrowedMut<'a> =3D &'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 { >> _p: PhantomData>, >> } >> >> -#[doc(hidden)] >> #[pin_data] >> #[repr(C)] >> -pub struct ArcInner { >> +struct ArcInner { > > I agree with this change, but let's mention it in the commit message. Right. > >> refcount: Opaque, >> 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 wh= ich meets the alignment >> -/// requirements of [`PointedTo`]. >> -/// >> -/// [`into_foreign`]: Self::into_foreign >> -/// [`PointedTo`]: Self::PointedTo >> +/// Implementers must ensure that [`Self::into_foreign`] return pointer= s 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 o= nly 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 [`fro= m_foreign`], [`try_from_foreign`], [`borrow`], or [`borrow_mut`] can result in undefin= ed behavior. Best regards, Andreas Hindborg