Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752021AbdHGWXS (ORCPT ); Mon, 7 Aug 2017 18:23:18 -0400 Received: from mail-io0-f177.google.com ([209.85.223.177]:35196 "EHLO mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751743AbdHGWXQ (ORCPT ); Mon, 7 Aug 2017 18:23:16 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170804231002.20362-1-labbott@redhat.com> <559096f0-bf1b-eff1-f0ce-33f53a4df255@redhat.com> From: Kees Cook Date: Mon, 7 Aug 2017 15:23:15 -0700 X-Google-Sender-Auth: PaExbwJmjHlioNoVdY02raO_7qE Message-ID: Subject: Re: [RFC][PATCH] mm/slub.c: Allow poisoning to use the fast path To: Laura Abbott Cc: Christopher Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux-MM , LKML , Rik van Riel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1433 Lines: 33 On Mon, Aug 7, 2017 at 3:00 PM, Laura Abbott wrote: > On 08/07/2017 11:03 AM, Christopher Lameter wrote: >> On Mon, 7 Aug 2017, Laura Abbott wrote: >> >>>> Ok I see that the objects are initialized with poisoning and redzoning but >>>> I do not see that there is fastpath code to actually check the values >>>> before the object is reinitialized. Is that intentional or am >>>> I missing something? >>> >>> Yes, that's intentional here. I see the validation as a separate more >>> expensive feature. I had a crude patch to do some checks for testing >>> and I know Daniel Micay had an out of tree patch to do some checks >>> as well. >> >> Ok then this patch does nothing? How does this help? > > The purpose of this patch is to ensure the poisoning can happen without > too much penalty. Even if there aren't checks to abort/warn when there > is a problem, there's still value in ensuring objects are always poisoned. To clarify, this is desirable to kill exploitation of exposure-after-free flaws and some classes of use-after-free flaws, since the contents will have be wiped out after a free. (Verification of poison is nice, but is expensive compared to the benefit against these exploits -- and notably doesn't protect against the other use-after-free attacks where the contents are changed after the next allocation, which would have passed the poison verification.) -Kees -- Kees Cook Pixel Security