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From: Benno Lossin <benno.lossin@proton.me>
To: Alice Ryhl <aliceryhl@google.com>
Cc: "Miguel Ojeda" <ojeda@kernel.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Wedson Almeida Filho" <wedsonaf@gmail.com>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Andreas Hindborg" <a.hindborg@samsung.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Carlos Llamas" <cmllamas@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Trevor Gross" <tmgross@umich.edu>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	rust-for-linux@vger.kernel.org,
	"Christian Brauner" <brauner@kernel.org>
Subject: Re: [PATCH v6 3/4] rust: uaccess: add typed accessors for userspace pointers
Date: Thu, 18 Apr 2024 16:23:06 +0000	[thread overview]
Message-ID: <c6239407-8410-49e2-a8a1-16be8468ab88@proton.me> (raw)
In-Reply-To: <CAH5fLgiMLxmmm0AVX_5HQF61FzzN69GCKabrr-uM_oV-rRMuHw@mail.gmail.com>

On 18.04.24 15:17, Alice Ryhl wrote:
> On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <benno.lossin@proton.me> wrote:
>>
>> On 18.04.24 10:59, Alice Ryhl wrote:
>>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
>>> index 8fad61268465..9c57c6c75553 100644
>>> --- a/rust/kernel/types.rs
>>> +++ b/rust/kernel/types.rs
>>> @@ -409,3 +409,67 @@ pub enum Either<L, R> {
>>>       /// Constructs an instance of [`Either`] containing a value of type `R`.
>>>       Right(R),
>>>   }
>>> +
>>> +/// Types for which any bit pattern is valid.
>>> +///
>>> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
>>> +/// reading arbitrary bytes into something that contains a `bool` is not okay.
>>> +///
>>> +/// It's okay for the type to have padding, as initializing those bytes has no effect.
>>> +///
>>> +/// # Safety
>>> +///
>>> +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
>>
>> What is the reason for disallowing interior mutability here? I agree
>> that it is necessary for `AsBytes`, but I don't think we need it here.
>> For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also
>> should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>`
>> already fails the "All bit-patterns must be valid for this type".
> 
> If T: FromBytes allows transmuting &[u8; size_of::<T>] into &T, then
> it would be a problem as you could then use it to modify the original
> &[u8].

Ahh that makes a lot of sense.

-- 
Cheers,
Benno



  reply	other threads:[~2024-04-18 16:23 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-18  8:59 [PATCH v6 0/4] Memory management patches needed by Rust Binder Alice Ryhl
2024-04-18  8:59 ` [PATCH v6 1/4] rust: uaccess: add userspace pointers Alice Ryhl
2024-04-19 17:11   ` Boqun Feng
2024-04-19 18:12     ` Alice Ryhl
2024-04-18  8:59 ` [PATCH v6 2/4] uaccess: always export _copy_[from|to]_user with CONFIG_RUST Alice Ryhl
2024-05-14 17:27   ` Andrew Morton
2024-05-15  7:34     ` Arnd Bergmann
2024-04-18  8:59 ` [PATCH v6 3/4] rust: uaccess: add typed accessors for userspace pointers Alice Ryhl
2024-04-18 13:01   ` Benno Lossin
2024-04-18 13:17     ` Alice Ryhl
2024-04-18 16:23       ` Benno Lossin [this message]
2024-04-18 17:19         ` Boqun Feng
2024-04-18 19:35           ` Alice Ryhl
2024-04-18 20:01             ` Boqun Feng
2024-04-18 17:52     ` Trevor Gross
2024-04-25 16:13   ` Gary Guo
2024-04-26  7:13     ` Alice Ryhl
2024-04-18  8:59 ` [PATCH v6 4/4] rust: add abstraction for `struct page` Alice Ryhl
2024-04-18 18:52   ` Boqun Feng
2024-04-18 22:08     ` Benno Lossin
2024-04-18 22:56       ` Boqun Feng
2024-04-18 23:04         ` Boqun Feng
2024-04-19  8:36           ` Benno Lossin
2024-04-19 17:23             ` Boqun Feng
2024-04-19 19:24               ` Benno Lossin
2024-04-19 19:35                 ` Boqun Feng
2024-04-25 16:20         ` Gary Guo

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