linux-hardening - Re: [PATCH v3 2/3] overflow: Introduce add_wrap(), sub_wrap(), and mul

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Date: Mon, 05 Feb 2024 23:21:41 +0000
From: Kees Cook <kees@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>, Kees Cook <keescook@...omium.org>
CC: linux-hardening@...r.kernel.org,
 Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
 Mark Rutland <mark.rutland@....com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] overflow: Introduce add_wrap(), sub_wrap(), and mul_wrap()

On February 5, 2024 11:17:12 PM GMT, Eric Biggers <ebiggers@...nel.org> wrote:
>On Mon, Feb 05, 2024 at 02:44:14PM -0800, Kees Cook wrote:
>> On Mon, Feb 05, 2024 at 12:21:45PM -0800, Eric Biggers wrote:
>> > On Mon, Feb 05, 2024 at 01:12:30AM -0800, Kees Cook wrote:
>> > > Subject: Re: [PATCH v3 2/3] overflow: Introduce add_wrap(), sub_wrap(), and mul_wrap()
>> > 
>> > Maybe these should be called wrapping_add, wrapping_sub, and wrapping_mul?
>> > Those names are more grammatically correct, and Rust chose those names too.
>> 
>> Sure, that works for me. What bout the inc_wrap() and dec_wrap() names?
>> I assume wrapping_inc() and wrapping_dec() ?
>> 
>
>Yes, though I'm not sure those should exist at all.  Maybe a += b should just
>become a = wrapping_add(a, b), instead of wrapping_inc(a, b)?
>wrapping_inc(a, b) isn't as self-explanatory.  Likewise for wrapping_dec.

It was to avoid repeating type information, as it would go from:

var_a += var_b;

to:

var_a = wrapping_add(typeof(var_a), var_a, var_b);

Which repeats "var_a" 3 times. :|

-- 
Kees Cook