linux-kernel - Re: [PATCH v2] minmax: clamp more efficiently by avoiding extra comparison

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Message-ID: <202209261130.2C96929E38@keescook>
Date:   Mon, 26 Sep 2022 11:30:58 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v2] minmax: clamp more efficiently by avoiding extra
 comparison

On Mon, Sep 26, 2022 at 02:23:48PM +0200, Jason A. Donenfeld wrote:
> On Mon, Sep 26, 2022 at 12:00 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > On Sat, Sep 24, 2022 at 12:37:26PM +0200, Jason A. Donenfeld wrote:
> > > On Fri, Sep 23, 2022 at 03:54:12PM -0700, Andrew Morton wrote:
> > > > On Fri, 23 Sep 2022 17:40:01 +0200 "Jason A. Donenfeld" <Jason@...c4.com> wrote:
> >
> > ...
> >
> > > Worth noting, by the way, is that the input validation check already
> > > caught a bug when 0day test bot choked:
> > >
> > > https://lore.kernel.org/linux-hwmon/20220924101151.4168414-1-Jason@zx2c4.com/
> >
> > Hooray, it was a good idea! :-)
> >
> > > So, options:
> > > 1) Keep this patch as-is, because it is useful on modern compilers.
> > > 2) Add an ifdef on compiler version, so we generate the best code in
> > >    each case.
> > > 3) Go back to testing twice, but keep the checker macro because it's
> > >    apparently useful.
> > > 4) Do nothing and discard this series.
> > >
> > > Any of those are okay with me. Opinions?
> >
> > I tend to case 3) (I believe you typo'ed double 2) cases) and apply the rest
> > as a separate change with all downsides explained (kinda 1) approach).
> 
> Alright, I'll do that. v3 on its way, then.

Cool. I've dropped v2 from my -next tree.

-- 
Kees Cook