linux-kernel - Re: [PATCH 2/2] rust: time: Use wrapping

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Message-ID: <202404151005.EB7F67A@keescook>
Date: Mon, 15 Apr 2024 10:08:30 -0700
From: Kees Cook <keescook@...omium.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Philipp Stanner <pstanner@...hat.com>, Kees Cook <kees@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Miguel Ojeda <ojeda@...nel.org>, John Stultz <jstultz@...gle.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Gary Guo <gary@...yguo.net>, bjorn3_gh@...tonmail.com,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: time: Use wrapping_sub() for Ktime::sub()

On Fri, Apr 12, 2024 at 09:58:57AM +0200, Miguel Ojeda wrote:
> On Fri, Apr 12, 2024 at 9:43 AM Philipp Stanner <pstanner@...hat.com> wrote:
> >
> > Is that going to remain enabled by default or what was the plan here?
> 
> The plan is to ideally keep it enabled by default, but I defer to Kees
> with whom we discussed this back then (Cc'd).

Yeah, we want to keep "trap on overflow" the default for Rust. We're
slowly making our way there[1] for C in Linux, so I don't want to
regress the Rust code.

> The goal is that Rust code, since the beginning, has all wrapping
> operations marked explicitly as such.

Exactly. We have to not perpetuate the ambiguity of arithmetic
operations. It should be clear from the operator or the type what the
expected bounds are for a calculation.

-Kees

[1] https://lore.kernel.org/lkml/20240205093725.make.582-kees@kernel.org/

-- 
Kees Cook