linux-kernel - Re: [RFC v4 PATCH 00/13] HARDENED

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Message-ID: <20161110203749.GV3117@twins.programming.kicks-ass.net>
Date:   Thu, 10 Nov 2016 21:37:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     kernel-hardening@...ts.openwall.com, keescook@...omium.org,
        arnd@...db.de, tglx@...utronix.de, mingo@...hat.com,
        h.peter.anvin@...el.com, will.deacon@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v4 PATCH 00/13] HARDENED_ATOMIC

On Thu, Nov 10, 2016 at 10:24:35PM +0200, Elena Reshetova wrote:
> This series brings the PaX/Grsecurity PAX_REFCOUNT
> feature support to the upstream kernel. All credit for the
> feature goes to the feature authors.
> 
> The name of the upstream feature is HARDENED_ATOMIC
> and it is configured using CONFIG_HARDENED_ATOMIC and
> HAVE_ARCH_HARDENED_ATOMIC.
> 
> This series only adds x86 support; other architectures are expected
> to add similar support gradually.
> 
> More information about the feature can be found in the following
> commit messages.

No, this should be here. As it stands this is completely without
content.

In any case, NAK on this approach. Its the wrong way around.

_IF_ you want to do a non-wrapping variant, it must not be the default.

Since you need to audit every single atomic_t user in the kernel anyway,
it doesn't matter. But changing atomic_t to non-wrap by default is not
robust, if you forgot one, you can then trivially dos the kernel.

That said, I still don't much like this.

I would much rather you make kref useful and use that. It still means
you get to audit all refcounts in the kernel, but hey, you had to do
that anyway.