linux-kernel - Re: [PATCH 5/7] rust: file: add `Kuid` wrapper

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Message-ID: <20231207074631.7xjqkkn4oaw32xm6@moria.home.lan>
Date:   Thu, 7 Dec 2023 02:46:31 -0500
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        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@...sung.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 5/7] rust: file: add `Kuid` wrapper

On Thu, Dec 07, 2023 at 08:18:37AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Dec 06, 2023 at 03:02:24PM -0500, Kent Overstreet wrote:
> > On Thu, Nov 30, 2023 at 11:36:35AM +0100, Peter Zijlstra wrote:
> > > On Wed, Nov 29, 2023 at 01:12:17PM +0000, Alice Ryhl wrote:
> > > 
> > > > diff --git a/rust/helpers.c b/rust/helpers.c
> > > > index fd633d9db79a..58e3a9dff349 100644
> > > > --- a/rust/helpers.c
> > > > +++ b/rust/helpers.c
> > > > @@ -142,6 +142,51 @@ void rust_helper_put_task_struct(struct task_struct *t)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
> > > >  
> > > > +kuid_t rust_helper_task_uid(struct task_struct *task)
> > > > +{
> > > > +	return task_uid(task);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(rust_helper_task_uid);
> > > > +
> > > > +kuid_t rust_helper_task_euid(struct task_struct *task)
> > > > +{
> > > > +	return task_euid(task);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(rust_helper_task_euid);
> > > 
> > > Aren't these like ideal speculation gadgets? And shouldn't we avoid
> > > functions like this for exactly that reason?
> > 
> > I think asking the Rust people to care about that is probably putting
> > too many constraints on them, unless you actually have an idea for
> > something better to do...
> 
> It's not a constraint, it is a "we can not do this as it is buggy
> because cpus are broken and we need to protect users from those bugs."
> 
> If we were to accept this type of code, then the people who are going
> "it's safer to write kernel code in Rust" would be "pleasantly
> surprised" when it turns out that their systems are actually more
> insecure.
> 
> Hint, when "known broken" code is found in code review, it can not just
> be ignored.

We're talking about a CPU bug, not a Rust bug, and maybe try a nm
--size-sort and see what you find before throwing stones at them...