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Wysocki" , "Miguel Ojeda" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Bjorn Helgaas" , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , "Abdiel Janulgue" , "Robin Murphy" , "David Airlie" , "Simona Vetter" , "Danilo Krummrich" , , , , , , Subject: Re: [PATCH v4 02/20] rust: io: add missing safety requirement in `IoCapable` methods From: "Alexandre Courbot" Content-Transfer-Encoding: quoted-printable References: <20260611-io_projection-v4-0-1f7224b02dcb@garyguo.net> <20260611-io_projection-v4-2-1f7224b02dcb@garyguo.net> In-Reply-To: <20260611-io_projection-v4-2-1f7224b02dcb@garyguo.net> X-ClientProxiedBy: TY4P286CA0016.JPNP286.PROD.OUTLOOK.COM (2603:1096:405:2b0::14) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|MN0PR12MB6366:EE_ X-MS-Office365-Filtering-Correlation-Id: 9b854fa2-9f14-4579-a3c4-08deca967f43 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|23010399003|10070799003|1800799024|56012099006|4143699003|11063799006|5023799004|6133799003|18002099003|22082099003; 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Add it so it can be relied on by implementor of > `IoCapable`. > > Expand the check `Io` by taking `self.addr()` into consideration when "the check performed by `Io`" maybe? > checking if `offset` is aligned. For the compile-time `io_addr_assert` > check, check using the known minimum alignment of `IO::Target` and the typo: s/IO/Io. > accessed type. > > While at it, fix the alignment check to use `align_of` instead of > `size_of`. The values match for all primitives (including u64, given that > we do not provide u64 accessor on 32-bit platforms), but are not > necessarily true for custom types. > > Signed-off-by: Gary Guo > --- > rust/kernel/io.rs | 25 ++++++++++++++++--------- > 1 file changed, 16 insertions(+), 9 deletions(-) > > diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs > index bef571dad6eb..fa9ae39ad9d2 100644 > --- a/rust/kernel/io.rs > +++ b/rust/kernel/io.rs > @@ -196,13 +196,14 @@ pub fn maxsize(&self) -> usize { > #[repr(transparent)] > pub struct Mmio(MmioRaw); > =20 > -/// Checks whether an access of type `U` at the given `offset` > +/// Checks whether an access of type `U` at the given `base` and the giv= en `offset` > /// is valid within this region. > +/// > +/// The `base` is used for alignment checking only. This can be set to 0= to skip the check. > #[inline] > -const fn offset_valid(offset: usize, size: usize) -> bool { > - let type_size =3D core::mem::size_of::(); > - if let Some(end) =3D offset.checked_add(type_size) { > - end <=3D size && offset % type_size =3D=3D 0 > +const fn offset_valid(base: usize, offset: usize, size: usize) -> boo= l { > + if let Some(end) =3D offset.checked_add(size_of::()) { > + end <=3D size && (base.wrapping_add(offset) % align_of::() = =3D=3D 0) > } else { > false > } > @@ -221,14 +222,16 @@ pub trait IoCapable { > /// > /// # Safety > /// > - /// The range `[address..address + size_of::()]` must be within t= he bounds of `Self`. > + /// - The range `[address..address + size_of::()]` must be within= the bounds of `Self`. > + /// - `address` must be aligned. > unsafe fn io_read(&self, address: usize) -> T; > =20 > /// Performs an I/O write of `value` at `address`. > /// > /// # Safety > /// > - /// The range `[address..address + size_of::()]` must be within t= he bounds of `Self`. > + /// - The range `[address..address + size_of::()]` must be within= the bounds of `Self`. > + /// - `address` must be aligned. > unsafe fn io_write(&self, value: T, address: usize); > } > =20 > @@ -310,7 +313,11 @@ pub trait Io { > // Always inline to optimize out error path of `build_assert`. > #[inline(always)] > fn io_addr_assert(&self, offset: usize) -> usize { > - build_assert!(offset_valid::(offset, Self::Target::MIN_SIZE))= ; > + // We cannot check alignment with `offset_valid` using `self.add= r()`. So set 0 for it and > + // ensure alignment by checking that the alignment of `U` is sma= ller or equal to the > + // alignment of `Self::Target`. > + const_assert!(Alignment::of::().as_usize() <=3D Self::Target:= :MIN_ALIGN.as_usize()); > + build_assert!(offset_valid::(0, offset, Self::Target::MIN_SIZ= E)); IIUC this can allow unaligned accesses if `self.addr()` itself is not properly aligned. Do we need a new `Io` invariant for that or is it already enforced somewhere?