From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753185AbdGFGrl (ORCPT ); Thu, 6 Jul 2017 02:47:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:43883 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750942AbdGFGrk (ORCPT ); Thu, 6 Jul 2017 02:47:40 -0400 Date: Thu, 6 Jul 2017 08:47:34 +0200 From: Michal Hocko To: Andrew Morton Cc: Linus Torvalds , Vlastimil Babka , Ben Hutchings , Willy Tarreau , Oleg Nesterov , Rik van Riel , LKML , linux-mm Subject: Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in the stack Message-ID: <20170706064733.GA29724@dhcp22.suse.cz> References: <20170705165602.15005-1-mhocko@kernel.org> <20170705182849.GA18027@dhcp22.suse.cz> <20170705141849.2e0e4721d975277183eb178f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170705141849.2e0e4721d975277183eb178f@linux-foundation.org> 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 On Wed 05-07-17 14:18:49, Andrew Morton wrote: > On Wed, 5 Jul 2017 20:28:49 +0200 Michal Hocko wrote: > > > "mm: enlarge stack guard gap" has introduced a regression in some rust > > and Java environments which are trying to implement their own stack > > guard page. They are punching a new MAP_FIXED mapping inside the > > existing stack Vma. > > > > This will confuse expand_{downwards,upwards} into thinking that the stack > > expansion would in fact get us too close to an existing non-stack vma > > which is a correct behavior wrt. safety. It is a real regression on > > the other hand. Let's work around the problem by considering PROT_NONE > > mapping as a part of the stack. This is a gros hack but overflowing to > > such a mapping would trap anyway an we only can hope that usespace > > knows what it is doing and handle it propely. > > > > Fixes: d4d2d35e6ef9 ("mm: larger stack guard gap, between vmas") > > That should be 1be7107fbe18, yes? yes. d4d2d35e6ef9 was a cherry-pick into the mmotm git tree. Sorry about that. > > Debugged-by: Vlastimil Babka > > Signed-off-by: Michal Hocko -- Michal Hocko SUSE Labs