linux-kernel - Re: [PATCH v2 2/3] binder: do not initialize locals passed to copy_from

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Message-ID: <202003040951.7857DFD936@keescook>
Date:   Wed, 4 Mar 2020 10:13:40 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        Jann Horn <jannh@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH v2 2/3] binder: do not initialize locals passed to
 copy_from_user()

On Tue, Mar 03, 2020 at 12:38:32PM +0300, Dan Carpenter wrote:
> The real fix is to initialize everything manually, the automated
> initialization is a hardenning feature which many people will disable.

I cannot disagree more with this sentiment. Linus has specifically said he
wants this initialization on by default[1], and the major thing holding
that back from happening is that no one working on GCC has had time to
add this feature there. All the kernels I know of that are built with
Clang (Android, Chrome OS, OpenMandriva) either already have this turned
on or have plans to do so shortly.

> So I don't think the hardenning needs to be perfect, it needs to simple
> and fast.

I think it should be able to be intelligently optimized, so I'm all for
finding ways to mark function arguments as "will be initialized" in some
fashion.

-Kees

[1] "Oh, I love that patch." https://lore.kernel.org/lkml/CA+55aFykZL+cSBJjBBts7ebEFfyGPdMzTmLSxKnT_29=j942dA@mail.gmail.com/

-- 
Kees Cook