linux-kernel - Re: [PATCH v2 1/3] overflow.h: Add arithmetic shift helper

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Message-ID: <CAGXu5j+=gBk=6Pva36HFj1L=Bz2O1+kzcUwUEu8eme_A4F5ktg@mail.gmail.com>
Date:   Wed, 1 Aug 2018 08:38:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        Bart Van Assche <Bart.VanAssche@....com>,
        Doug Ledford <dledford@...hat.com>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] overflow.h: Add arithmetic shift helper

On Wed, Aug 1, 2018 at 1:07 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> On Wed, Aug 01, 2018 at 10:57:44AM +0300, Dan Carpenter wrote:
>> The idea is nice, but I don't like the API.  The "_overflow" feels too
>> specific because maybe we could check for other things in the future.
>> Normally boolean macros should say they are boolean in the name and I
>> would prefer if it returned zero on failure.
>>
>>       if (!checked_shift(dest, mask, shift)) {
>>       if (!shift_ok(dest, mask, shift)) {
>>       if (!safe_shift(dest, mask, shift)) {
>
> Huh...  It turns out I put the argument order different as well.
>
> If we wanted to keep it returning 1 on failure then some other names
> are:
>
>         if (shift_failed(dest, mask, shift)) {
>         if (shift_error(dest, mask, shift)) {
>         if (shift_overflow(dest, mask, shift)) {

This is following the existing check_{add,mul}_overflow() helpers,
which are based on the gcc helpers. I'd like to keep things
consistent.

-Kees

-- 
Kees Cook
Pixel Security