kernel-hardening - Re: [PATCH v9] x86/asm: Implement fast refcount overflow protection

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Message-ID: <CAGXu5j+BRkTM3X6NuHoyU4FTs154wQtunOKF2cQDaHKyKNzpFQ@mail.gmail.com>
Date: Wed, 2 Aug 2017 11:54:24 -0700
From: Kees Cook <keescook@...omium.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...hat.com>, 
	Christoph Hellwig <hch@...radead.org>, "Eric W. Biederman" <ebiederm@...ssion.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Jann Horn <jannh@...gle.com>, 
	Eric Biggers <ebiggers3@...il.com>, Elena Reshetova <elena.reshetova@...el.com>, 
	Hans Liljestrand <ishkamiel@...il.com>, Greg KH <gregkh@...uxfoundation.org>, 
	Alexey Dobriyan <adobriyan@...il.com>, "Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com, 
	Davidlohr Bueso <dave@...olabs.net>, Manfred Spraul <manfred@...orfullife.com>, 
	"axboe@...nel.dk" <axboe@...nel.dk>, James Bottomley <James.Bottomley@...senpartnership.com>, 
	"x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>, "David S. Miller" <davem@...emloft.net>, 
	Rik van Riel <riel@...hat.com>, LKML <linux-kernel@...r.kernel.org>, 
	linux-arch <linux-arch@...r.kernel.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v9] x86/asm: Implement fast refcount overflow protection

On Tue, Jul 25, 2017 at 1:55 PM, Kees Cook <keescook@...omium.org> wrote:
> This implements refcount_t overflow protection on x86 without a noticeable
> performance impact, though without the fuller checking of REFCOUNT_FULL.
> This is done by duplicating the existing atomic_t refcount implementation
> but with normally a single instruction added to detect if the refcount
> has gone negative (e.g. wrapped past INT_MAX or below zero). When detected,
> the handler saturates the refcount_t to INT_MIN / 2. With this overflow
> protection, the erroneous reference release that would follow a wrap back
> to zero is blocked from happening, avoiding the class of refcount-overflow
> use-after-free vulnerabilities entirely.

Hi Ingo,

Friendly ping. Is there anything remaining for this patch to go into -tip?

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

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