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Message-ID: <2025050619-eraser-kissing-006e@gregkh>
Date: Tue, 6 May 2025 19:57:15 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Arnd Bergmann <arnd@...db.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>,
Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uaccess: rust: use newtype for user pointers
On Tue, May 06, 2025 at 01:25:58PM +0000, Alice Ryhl wrote:
> In C code we use sparse with the __user annotation to detect cases where
> a user pointer is mixed up with other things. To replicate that, we
> introduce a new struct UserPtr that serves the same purpose using the
> newtype pattern.
>
> The UserPtr type is not marked with #[derive(Debug)], which means that
> it's not possible to print values of this type. This avoids ASLR
> breakage.
>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> rust/kernel/uaccess.rs | 48 ++++++++++++++++++++++++++++++++++------
> samples/rust/rust_misc_device.rs | 4 +++-
> 2 files changed, 44 insertions(+), 8 deletions(-)
>
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index 978205289d297a4001a51fa40ac29039bff73672..2914a35de3dfbc7860ebf0d6e11cc65d409e9481 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -14,8 +14,38 @@
> };
> use core::mem::{size_of, MaybeUninit};
>
> -/// The type used for userspace addresses.
> -pub type UserPtr = usize;
> +/// A pointer into userspace.
> +///
> +/// This is the Rust equivalent to C pointers tagged with `__user`.
> +#[repr(transparent)]
> +#[derive(Copy, Clone)]
> +pub struct UserPtr(pub usize);
Again, why can't this be:
pub struct UserPtr(pub *const u8);
This is a pointer to a stream of u8 bytes, so let's treat it like that
as that is what we are copying from here.
thanks,
greg k-h
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