linux-kernel - Re: [GIT PULL] usercopy fixes for v4.8-rc6-part2

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Message-ID: <CAGXu5j+iKpW90FMRYRD9Gru489jiKdvAr9wth1ygE9vxOg2PXA@mail.gmail.com>
Date:   Wed, 7 Sep 2016 14:32:07 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vinson Lee <vlee@...edesktop.org>
Subject: Re: [GIT PULL] usercopy fixes for v4.8-rc6-part2

On Wed, Sep 7, 2016 at 12:15 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Sep 7, 2016 at 11:36 AM, Kees Cook <keescook@...omium.org> wrote:
>>
>> - move page-spanning check behind a CONFIG since it's triggering false positives
>
> Hmm. I pulled this, but looking at it I realized that
>
> +       depends on !COMPILE_TEST
>
> doesn't make any real sense to me.
>
> All it does is make sure that "make allmodconfig" doesn't actually
> test that the PAGESPAN code compiles.
>
> It's not like that is a big cost for allmodconfig builds, but it does
> mean that it gets less coverage.
>
> And it really makes no sense to me. We *don't* want to run with that
> option enabled normally.
>
> I think what you actually meant was something like
>
> +       depends on EXPERT
>
> which means that it does *not* get enabled in normal user builds.
>
> Hmm?

I guess that's true -- I was trying to think of a way to make sure it
didn't get tested by 0-day syscall fuzzer on a randconfig, since I
didn't want the noise. But now that I double-check this, yeah, it
looks like randconfig doesn't set COMPILE_TEST. Hmpf.

I will send another patch to flip this to EXPERT, and if 0-day finds
issues, I can add them to the __GPF_COMP hit-list. :P

-Kees

-- 
Kees Cook
Nexus Security