linux-hardening - Re: [PATCH v8 3/5] rust: add bitmap API.

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Message-ID: <CACQBu=VXAPfVGxVFiW4iZWF=kd4ZdwH4xwz0YgXnoqK1UnHRkA@mail.gmail.com>
Date: Mon, 19 May 2025 23:49:29 +0200
From: Burak Emir <bqe@...gle.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Jann Horn <jannh@...gle.com>, Yury Norov <yury.norov@...il.com>, Kees Cook <kees@...nel.org>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Viresh Kumar <viresh.kumar@...aro.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...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@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	"Gustavo A . R . Silva" <gustavoars@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v8 3/5] rust: add bitmap API.

On Mon, May 19, 2025 at 11:42 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Mon, May 19, 2025 at 10:08 PM Burak Emir <bqe@...gle.com> wrote:
> >
> > The "unsafe" here should serve as reminder to argue why it is ok to
> > not have any ordering guarantees.
>
> `unsafe` should be used for unsafe functions, not as a general
> "danger" or "advanced" marker.
>
> (Having such a marker could be useful, but `unsafe fn` is not it)
>

I can see the appeal of having a strict definition "safe = no UB".

> > The last sentence is supposed to say: when you have a &mut bitmap, you
> > can reborrow it as &bitmap, and then happily call this atomic op.
> > Even though it is unnecessary.
>
> I don't think that is related to safety preconditions. A "# Safety"
> section is intended to explain what the preconditions are.
>
> So, for instance, stating "The caller must ensure that this is safe"
> does not add much.

I see what you are saying. Not being sensitive to order is a
precondition to a property.
There are many different kinds of (colloquial) safety e.g. crash
safety or data integrity.

Sticking to a technical definition of safety has the advantage that
one can be consistent.
So I'll remove the unsafe marker then.

Thanks,
- Burak