linux-hardening - Re: [PATCH v5 3/3] overflow: Introduce wrapping_inc() and wrapping

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Date: Wed, 7 Feb 2024 08:08:14 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Andy Shevchenko <andy@...nel.org>,
	Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
	Marco Elver <elver@...gle.com>, Eric Biggers <ebiggers@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] overflow: Introduce wrapping_inc() and
 wrapping_dec()

On Wed, Feb 07, 2024 at 05:31:54PM +0200, Andy Shevchenko wrote:
> On Wed, Feb 7, 2024 at 5:24 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > This allows replacements of the idioms "var += offset" and "var -= offset"
> > with the wrapping_inc() and wrapping_dec() helpers respectively. They
> > will avoid wrap-around sanitizer instrumentation.
> >
> > Add to the selftests to validate behavior and lack of side-effects.
> 
> I would expect inc/dec to add/subtract 1. So, to me the terminology is
> confusing. The list of the C/C++ operators on Wikipedia describes
> above as
> 
> += Assignment by sum
> -= Assignment by difference
> 
> 
> Hence the proposal is to have
> 
> wrapping_sum()
> wrapping_diff()

I think maybe the missing phrase is "assign", which is what makes
argument 1 "special" -- it's being changed. Perhaps:

wrapping_add_assign()
wrapping_sub_assign()

?

-- 
Kees Cook