From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f54.google.com (mail-wr1-f54.google.com [209.85.221.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0B9921E0BD for ; Sat, 10 May 2025 09:33:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.54 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746869590; cv=none; b=i1zSUrBjJxrE2myCGU33C6Aokay+PfaARMLdJjquekoScz+VlKkEhjP+VUD3vNHrV7sdO5eoSGvBEVo12GxTvNItFvhMnm7SzYIRWuku5ZDVZv1lLOt1Idrk+OdZV8B6ekAnz3XUHP01KWUObth9MB9mG5JvZYXAPFtYke6GGec= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746869590; c=relaxed/simple; bh=dWjiyob69G2GucTul/lsXlGpP89mKJGQ4P8+IWoJ7pA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=FGAGGaKjsnpgf/86IdMBITrzgTINruUJoro3rYrVEIo0bepyoJlK1vFY9HV/8Xeqn806nwl59DKxN9xalCu++qSddl/YWKGR2yJY4xVgcFktFFqDY+HhrI/81JXeqBoj+Ou4ENWlgxfQBqh5WWpcdu27KHFaK8+UJLrk50MJvbc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Ta4cDlaB; arc=none smtp.client-ip=209.85.221.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Ta4cDlaB" Received: by mail-wr1-f54.google.com with SMTP id ffacd0b85a97d-3a1b8e8b2b2so1284739f8f.2 for ; Sat, 10 May 2025 02:33:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1746869587; x=1747474387; darn=lists.linux.dev; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=SOE7sdT8D61vDqGwsVaxjwgujETa56pyZ4FYk1rPCD4=; b=Ta4cDlaBtkcRCyM02ASxEzASA5G/ZuDb4pRkLKSasNyiAqw47WR6HhFuBO2pPYx9Jb MeyawttpfWyf3AUtnzycnAunb03365WIX3Lo4ZrC5HuBx68hCI+mvmjF15LPy6kpf2qf +JY7DBUhKNI+o2U4JHVZFAG6WE6Rd4hUm54HzQ5yhjqkJ/bKdjHq+G2FkJViAUCaOdqc h3oRVtn2lveShyXKAzDq1ktF3HcYihQvjKYEgkXgaMLlAq2z5Eb4Bolzu+tbtmVKfrRp Vcfuq2fJnltHgdJdk3Mzzb3X8vUtlLNKgVbuyFwm1LXTGf4N/Odx0gp5OHzIJ16GsYFO kXfQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746869587; x=1747474387; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=SOE7sdT8D61vDqGwsVaxjwgujETa56pyZ4FYk1rPCD4=; b=DuXAvOWs29xv5RIwj79Ghr0+h3H1gNBoWoVmpxq2/3wyyAxZ2oUHw3Sk0lt3q/Nq0y 4bW/vuONiv67GpBKGn2hWsFNmdC+mikzG3KpA4EI2WEmegHaZJxLkpIpbNam/a6gwixX /2fpcbfpTnPOi/JUJnD1+dwiI/+vdOdropPzpd3rLbh0ALhAlpo7dTmVVpMcZJXMq5ZO ChOVb2K9Wpx4iVk4Ibd5Qhz4O4qS4u8HuVYqMO7evNizow9N4vjftSptXQitbgsBn7oF 8GzeHCcPp9dddFIBG6FxwMTpvv9qMs53ft8+7qdDXVFIftFbkpo+eyp04BX7//PpP7Ye Zdcg== X-Forwarded-Encrypted: i=1; AJvYcCWi9MvkOpfm0e+1GkvkNG25AOMZi6ZP4lD0MN3c5bUujOn8foC9FzopjPJghqtVS3KDwI/c@lists.linux.dev X-Gm-Message-State: AOJu0YycsVNGdfTbbgszprXCuXyLRQrRiBk5p8s0oADROxbJ8fgybhhs hJ1eTeA3Q3xchhEjIvAOJ1uxUVBe8tjuaoveXp2Pm8e4bMiY4Yz8 X-Gm-Gg: ASbGncs5FHWjcCCXd+hkyuL2D79Ep5g9+oYHSh0tMMAFdQtmD6HWMQGs8bGUBNZdB/N fQ0Ceb7T9M87KRh8HkqaXryQroJTrL4Ybg46H5y9Sjt2fVXM1+GCIUIyAKEXX2gMLk1fIn6ihQn qrpYCnW8P8wSSSFHeC45veJ2VYMUmsjr6uBbHPXTuTVNTOsLlin90ocvAI1hBe+n2OfWPAlPcY1 n6eSho2LfdCepcZm4ua7GNgt8BL8SKiQTCmlt/00sW/NhW9pFIM9MpwQphwP0or1Xd5i1CZS0aU MMTN4RiCC2CvlRek9t5rW2qe+iLJl0oQAK699Rs= X-Google-Smtp-Source: AGHT+IFVbblIDN2ouLSx9sgtkfmF6TDVCexrpp5Doe3paIz95KUyn+eXRyz6dYaHj9TZC+ejqCcpgg== X-Received: by 2002:a05:6000:401e:b0:3a0:aee0:c647 with SMTP id ffacd0b85a97d-3a1f64374e1mr5493421f8f.17.1746869586609; Sat, 10 May 2025 02:33:06 -0700 (PDT) Received: from [10.0.1.56] ([2001:871:22a:99c5::1ad1]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-3a1f57ddde0sm5981485f8f.14.2025.05.10.02.33.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 May 2025 02:33:06 -0700 (PDT) From: Christian Schrefl Date: Sat, 10 May 2025 11:32:26 +0200 Subject: [PATCH v3 1/3] rust: add UnsafePinned type Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20250510-rust_unsafe_pinned-v3-1-57ce151123f9@gmail.com> References: <20250510-rust_unsafe_pinned-v3-0-57ce151123f9@gmail.com> In-Reply-To: <20250510-rust_unsafe_pinned-v3-0-57ce151123f9@gmail.com> To: Sky , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , =?utf-8?q?Gerald_Wisb=C3=B6ck?= , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev, Christian Schrefl X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1746869583; l=8523; i=chrisi.schrefl@gmail.com; s=20250119; h=from:subject:message-id; bh=dWjiyob69G2GucTul/lsXlGpP89mKJGQ4P8+IWoJ7pA=; b=qz6jwCq5QCTjxafiO7g3wJAMoBTTNDpYvHhtgDrKF8imb7cwNHmpLvQ6G4jXPxK2xqz+C6zf/ cgmCZYY7ltoAhopI0I0sjxOMih2ndKndO8ovfWHIXrlA7XwFUdnc4qu X-Developer-Key: i=chrisi.schrefl@gmail.com; a=ed25519; pk=EIyitYCrzxWlybrqoGqiL2jyvO7Vp9X40n0dQ6HE4oU= `UnsafePinned` is useful for cases where a value might be shared with C code but not directly used by it. In particular this is added for storing additional data in the `MiscDeviceRegistration` which will be shared between `fops->open` and the containing struct. Similar to `Opaque` but guarantees that the value is always initialized and that the inner value is dropped when `UnsafePinned` is dropped. This was originally proposed for the IRQ abstractions [0] and is also useful for other where the inner data may be aliased, but is always valid and automatic `Drop` is desired. Since then the `UnsafePinned` type was added to upstream Rust [1] by Sky as a unstable feature, therefore this patch implements the subset of the upstream API for the `UnsafePinned` type required for additional data in `MiscDeviceRegistration` and in the implementation of the `Opaque` type. Some differences to the upstream type definition are required in the kernel implementation, because upstream type uses some compiler changes to opt out of certain optimizations, this is documented in the documentation and a comment on the `UnsafePinned` type. The documentation on is based on the upstream rust documentation with minor modifications for the kernel implementation. Link: https://lore.kernel.org/rust-for-linux/CAH5fLgiOASgjoYKFz6kWwzLaH07DqP2ph+3YyCDh2+gYqGpABA@mail.gmail.com [0] Link: https://github.com/rust-lang/rust/pull/137043 [1] Suggested-by: Alice Ryhl Reviewed-by: Gerald Wisböck Reviewed-by: Alice Ryhl Co-developed-by: Sky Signed-off-by: Sky Signed-off-by: Christian Schrefl --- rust/kernel/types.rs | 6 ++ rust/kernel/types/unsafe_pinned.rs | 113 +++++++++++++++++++++++++++++++++++++ 2 files changed, 119 insertions(+) diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 9d0471afc9648f2973235488b441eb109069adb1..705f420fdfbc4a576de1c4546578f2f04cdf615e 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -253,6 +253,9 @@ fn drop(&mut self) { /// /// [`Opaque`] is meant to be used with FFI objects that are never interpreted by Rust code. /// +/// In cases where the contained data is only used by Rust, is not allowed to be +/// uninitialized and automatic [`Drop`] is desired [`UnsafePinned`] should be used instead. +/// /// It is used to wrap structs from the C side, like for example `Opaque`. /// It gets rid of all the usual assumptions that Rust has for a value: /// @@ -578,3 +581,6 @@ pub enum Either { /// [`NotThreadSafe`]: type@NotThreadSafe #[allow(non_upper_case_globals)] pub const NotThreadSafe: NotThreadSafe = PhantomData; + +mod unsafe_pinned; +pub use unsafe_pinned::UnsafePinned; diff --git a/rust/kernel/types/unsafe_pinned.rs b/rust/kernel/types/unsafe_pinned.rs new file mode 100644 index 0000000000000000000000000000000000000000..612b67b400ff361335803c29799b6aeb375ed52c --- /dev/null +++ b/rust/kernel/types/unsafe_pinned.rs @@ -0,0 +1,113 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +//! The contents of this file partially come from the Rust standard library, hosted in +//! the repository, licensed under +//! "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details, +//! see . +//! +//! This file provides a implementation / polyfill of a subset of the upstream +//! rust `UnsafePinned` type. For details on the difference to the upstream +//! implementation see the comment on the [`UnsafePinned`] struct definition. + +use core::{cell::UnsafeCell, marker::PhantomPinned}; +use pin_init::{cast_pin_init, PinInit, Wrapper}; + +/// This type provides a way to opt-out of typical aliasing rules; +/// specifically, `&mut UnsafePinned` is not guaranteed to be a unique pointer. +/// +/// However, even if you define your type like `pub struct Wrapper(UnsafePinned<...>)`, it is still +/// very risky to have an `&mut Wrapper` that aliases anything else. Many functions that work +/// generically on `&mut T` assume that the memory that stores `T` is uniquely owned (such as +/// `mem::swap`). In other words, while having aliasing with `&mut Wrapper` is not immediate +/// Undefined Behavior, it is still unsound to expose such a mutable reference to code you do not +/// control! Techniques such as pinning via [`Pin`](core::pin::Pin) are needed to ensure soundness. +/// +/// Similar to [`UnsafeCell`], [`UnsafePinned`] will not usually show up in +/// the public API of a library. It is an internal implementation detail of libraries that need to +/// support aliasing mutable references. +/// +/// Further note that this does *not* lift the requirement that shared references must be read-only! +/// Use [`UnsafeCell`] for that. +/// +/// This type blocks niches the same way [`UnsafeCell`] does. +/// +/// # Kernel implementation notes +/// +/// This implementation works because of the "`!Unpin` hack" in rustc, which allows (some kinds of) +/// mutual aliasing of `!Unpin` types. This hack might be removed at some point, after which only +/// the `core::pin::UnsafePinned` type will allow this behavior. In order to simplify the migration +/// to future rust versions only this polyfill of this type should be used when this behavior is +/// required. +// +// As opposed to the upstream Rust type this contains a `PhantomPinned` and `UnsafeCell` +// - `PhantomPinned` to ensure the struct always is `!Unpin` and thus enables the `!Unpin` hack. +// This causes the LLVM `noalias` and `dereferenceable` attributes to be removed from +// `&mut !Unpin` types. +// - In order to disable niche optimizations this implementation uses `UnsafeCell` internally, +// the upstream version however currently does not. This will most likely change in the future +// but for now we don't expose this in the documentation, since adding the guarantee is simpler +// than removing it. Meaning that for now the fact that `UnsafePinned` contains an `UnsafeCell` +// must not be relied on (Other than the niche blocking). +// See this Rust tracking issue: https://github.com/rust-lang/rust/issues/137750 +#[repr(transparent)] +pub struct UnsafePinned { + _ph: PhantomPinned, + value: UnsafeCell, +} + +impl UnsafePinned { + /// Constructs a new instance of [`UnsafePinned`] which will wrap the specified value. + /// + /// All access to the inner value through `&UnsafePinned` or `&mut UnsafePinned` or + /// `Pin<&mut UnsafePinned>` requires `unsafe` code. + #[inline(always)] + #[must_use] + pub const fn new(value: T) -> Self { + UnsafePinned { + value: UnsafeCell::new(value), + _ph: PhantomPinned, + } + } +} +impl UnsafePinned { + /// Get read-only access to the contents of a shared `UnsafePinned`. + /// + /// Note that `&UnsafePinned` is read-only if `&T` is read-only. This means that if there is + /// mutation of the `T`, future reads from the `*const T` returned here are UB! Use + /// [`UnsafeCell`] if you also need interior mutability. + /// + /// [`UnsafeCell`]: core::cell::UnsafeCell + /// + /// ```rust,no_build + /// use kernel::types::UnsafePinned; + /// + /// unsafe { + /// let mut x = UnsafePinned::new(0); + /// let ptr = x.get(); // read-only pointer, assumes immutability + /// x.get_mut_unchecked().write(1); + /// ptr.read(); // UB! + /// } + /// ``` + /// + /// Note that the `get_mut_unchecked` function used by this example is + /// currently not implemented in the kernel implementation. + #[inline(always)] + #[must_use] + pub const fn get(&self) -> *const T { + self.value.get() + } + + /// Gets a mutable pointer to the wrapped value. + #[inline(always)] + #[must_use] + pub const fn raw_get_mut(this: *mut Self) -> *mut T { + this as *mut T + } +} + +impl Wrapper for UnsafePinned { + fn pin_init(init: impl PinInit) -> impl PinInit { + // SAFETY: `UnsafePinned` has a compatible layout to `T`. + unsafe { cast_pin_init(init) } + } +} -- 2.49.0