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Message-ID: <12b5bbc8-3661-4d67-a402-cecae692e75a@gmail.com>
Date: Wed, 7 Feb 2024 16:05:19 -0300
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Subject: Re: [PATCH v4 7/9] rust: file: add `Kuid` wrapper
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To: Alice Ryhl <aliceryhl@google.com>, 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?Q?Arve_Hj=C3=B8nnev=C3=A5g?= <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>
Cc: Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org,
 rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org
References: <20240202-alice-file-v4-0-fc9c2080663b@google.com>
 <20240202-alice-file-v4-7-fc9c2080663b@google.com>
From: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
In-Reply-To: <20240202-alice-file-v4-7-fc9c2080663b@google.com>
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On 2/2/24 07:55, Alice Ryhl wrote:
> 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.
> 
> Link: https://lore.kernel.org/all/202312080947.674CD2DC7@keescook/ [1]
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> [...]

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>