Received-SPF: pass (google.com: domain of linux-kernel+bounces-60337-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
References: <20240209-alice-file-v5-0-a37886783025@google.com> <20240209-alice-file-v5-7-a37886783025@google.com>
In-Reply-To: <20240209-alice-file-v5-7-a37886783025@google.com>
From: Trevor Gross <tmgross@umich.edu>
Date: Sat, 10 Feb 2024 01:43:14 -0600
Message-ID: <CALNs47tTTbWL3T9rk_ismPT0Bwi8Kcm5aT9k8jfPsh=1wKvrPA@mail.gmail.com>
Subject: Re: [PATCH v5 7/9] rust: file: add `Kuid` wrapper
To: Alice Ryhl <aliceryhl@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, 
	Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@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>, 
	Peter Zijlstra <peterz@infradead.org>, Alexander Viro <viro@zeniv.linux.org.uk>, 
	Christian Brauner <brauner@kernel.org>, 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>, Dan Williams <dan.j.williams@intel.com>, 
	Kees Cook <keescook@chromium.org>, Matthew Wilcox <willy@infradead.org>, 
	Thomas Gleixner <tglx@linutronix.de>, Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org, 
	rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, 
	Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Fri, Feb 9, 2024 at 5:22=E2=80=AFAM Alice Ryhl <aliceryhl@google.com> wr=
ote:
>
> Adds a wrapper around `kuid_t` called `Kuid`. This allows us to define
> various operations on kuids such as equality and current_euid. It also
> lets us provide conversions from kuid into userspace values.
>
> Rust Binder needs these operations because it needs to compare kuids for
> equality, and it needs to tell userspace about the pid and uid of
> incoming transactions.
>
> To read kuids from a `struct task_struct`, you must currently use
> various #defines that perform the appropriate field access under an RCU
> read lock. Currently, we do not have a Rust wrapper for rcu_read_lock,
> which means that for this patch, there are two ways forward:
>
>  1. Inline the methods into Rust code, and use __rcu_read_lock directly
>     rather than the rcu_read_lock wrapper. This gives up lockdep for
>     these usages of RCU.
>
>  2. Wrap the various #defines in helpers and call the helpers from Rust.
>
> This patch uses the second option. One possible disadvantage of the
> second option is the possible introduction of speculation gadgets, but
> as discussed in [1], the risk appears to be acceptable.
>
> Of course, once a wrapper for rcu_read_lock is available, it is
> preferable to use that over either of the two above approaches.

Is this worth a FIXME?

> Link: https://lore.kernel.org/all/202312080947.674CD2DC7@keescook/ [1]
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Reviewed-by: Trevor Gross <tmgross@umich.edu>