Received-SPF: pass (google.com: domain of linux-kernel+bounces-106556-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240311-alice-mm-v3-0-cdf7b3a2049c@google.com>
 <20240311-alice-mm-v3-1-cdf7b3a2049c@google.com> <ZfiPB_iavHr8hNbm@boqun-archlinux>
In-Reply-To: <ZfiPB_iavHr8hNbm@boqun-archlinux>
From: Alice Ryhl <aliceryhl@google.com>
Date: Mon, 18 Mar 2024 20:12:27 +0100
Message-ID: <CAH5fLghs7=V2hHYBnQE-h=xpQYKX5ZxrV1iVdB4ybt7pAXFMWQ@mail.gmail.com>
Subject: Re: [PATCH v3 1/4] rust: uaccess: add userspace pointers
To: Boqun Feng <boqun.feng@gmail.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>, Gary Guo <gary@garyguo.net>, 
	=?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, 
	Benno Lossin <benno.lossin@proton.me>, Andreas Hindborg <a.hindborg@samsung.com>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <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>, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, 
	Christian Brauner <brauner@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Mon, Mar 18, 2024 at 7:59=E2=80=AFPM Boqun Feng <boqun.feng@gmail.com> w=
rote:
>
> On Mon, Mar 11, 2024 at 10:47:13AM +0000, Alice Ryhl wrote:
> > +
> > +    /// Reads raw data from the user slice into a raw kernel buffer.
> > +    ///
> > +    /// Fails with `EFAULT` if the read encounters a page fault.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// The `out` pointer must be valid for writing `len` bytes.
> > +    pub unsafe fn read_raw(&mut self, out: *mut u8, len: usize) -> Res=
ult {
>
> I don't think we want to promote the pub usage of this unsafe function,
> right? We can provide a safe version:
>
>         pub fn read_slice(&mut self, to: &[u8]) -> Result
>
> and all users can just use the safe version (with the help of
> slice::from_raw_parts_mut() if necessary).

Personally, I think having the function be unsafe is plenty discouragement.

Also, this method would need an &mut [u8], which opens the can of
worms related to uninitialized memory. The _raw version of this method
is strictly more powerful.

I don't think I actually use it directly in Binder, so I can make it
private if you think that's important. It needs to be pub(crate),
though, since it is used in `Page`.

Alice