Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752468AbdGDMAM (ORCPT ); Tue, 4 Jul 2017 08:00:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:52795 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752431AbdGDMAK (ORCPT ); Tue, 4 Jul 2017 08:00:10 -0400 Date: Tue, 4 Jul 2017 14:00:00 +0200 From: Michal Hocko To: Ben Hutchings Cc: Willy Tarreau , Linus Torvalds , Hugh Dickins , Oleg Nesterov , "Jason A. Donenfeld" , Rik van Riel , Larry Woodman , "Kirill A. Shutemov" , Tony Luck , "James E.J. Bottomley" , Helge Diller , James Hogan , Laura Abbott , Greg KH , "security@kernel.org" , linux-distros@vs.openwall.org, Qualys Security Advisory , LKML , Ximin Luo Subject: Re: [PATCH] mm: larger stack guard gap, between vmas Message-ID: <20170704115959.GM14722@dhcp22.suse.cz> References: <1498009101.2655.6.camel@decadent.org.uk> <20170621092419.GA22051@dhcp22.suse.cz> <1498042057.2655.8.camel@decadent.org.uk> <1499126133.2707.20.camel@decadent.org.uk> <20170704084122.GC14722@dhcp22.suse.cz> <20170704093538.GF14722@dhcp22.suse.cz> <20170704094728.GB22013@1wt.eu> <20170704104211.GG14722@dhcp22.suse.cz> <20170704113611.GA4732@decadent.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170704113611.GA4732@decadent.org.uk> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1483 Lines: 35 On Tue 04-07-17 12:36:11, Ben Hutchings wrote: > On Tue, 2017-07-04 at 12:42 +0200, Michal Hocko wrote: > > On Tue 04-07-17 11:47:28, Willy Tarreau wrote: > > > On Tue, Jul 04, 2017 at 11:35:38AM +0200, Michal Hocko wrote: > [...] > > > But wouldn't this completely disable the check in case such a guard page > > > is installed, and possibly continue to allow the collision when the stack > > > allocation is large enough to skip this guard page ? > > > > Yes and but a PROT_NONE would fault and as the changelog says, we _hope_ > > that userspace does the right thing. > > It may well not be large enough, because of the same wrong assumptions > that resulted in the kernel's guard page not being large enough. We > should count it as part of the guard gap but not a substitute. yes, you are right of course. But isn't this a bug on their side considering they are managing their _own_ stack gap? Our stack gap management is a best effort thing and two such approaches competing will always lead to weird cornercases. That was my assumption when saying that I am not sure this is really _worth_ it. We should definitely try to workaround clashes but that's about it. If others think that we should do everything to prevent even those issues I will not oppose of course. It just adds more cycles to something that is a weird case already. [...] > This *doesn't* fix the LibreOffice regression on i386. Are there any details about this regression? -- Michal Hocko SUSE Labs