Re: [PATCH v3 7/9] rust: file: add `Kuid` wrapper

[Benno Lossin]

On 18.01.24 15:36, 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]
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
>   rust/bindings/bindings_helper.h |  1 +
>   rust/helpers.c                  | 45 ++++++++++++++++++++
>   rust/kernel/cred.rs             |  5 ++-
>   rust/kernel/task.rs             | 74 ++++++++++++++++++++++++++++++++-
>   4 files changed, 122 insertions(+), 3 deletions(-)

Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>

-- 
Cheers,
Benno