Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752531AbdGDKq6 (ORCPT ); Tue, 4 Jul 2017 06:46:58 -0400 Received: from mx2.suse.de ([195.135.220.15]:44710 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752331AbdGDKq5 (ORCPT ); Tue, 4 Jul 2017 06:46:57 -0400 Date: Tue, 4 Jul 2017 12:46:52 +0200 From: Michal Hocko To: Linus Torvalds Cc: Ben Hutchings , Hugh Dickins , Willy Tarreau , 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 Subject: Re: [PATCH] mm: larger stack guard gap, between vmas Message-ID: <20170704104652.GH14722@dhcp22.suse.cz> References: <20170619142358.GA32654@1wt.eu> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170704093538.GF14722@dhcp22.suse.cz> 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: 1855 Lines: 40 On Tue 04-07-17 11:35:38, Michal Hocko wrote: > On Tue 04-07-17 10:41:22, Michal Hocko wrote: > > On Mon 03-07-17 17:05:27, Linus Torvalds wrote: > > > On Mon, Jul 3, 2017 at 4:55 PM, Ben Hutchings wrote: > > > > > > > > Firstly, some Rust programs are crashing on ppc64el with 64 KiB pages. > > > > Apparently Rust maps its own guard page at the lower limit of the stack > > > > (determined using pthread_getattr_np() and pthread_attr_getstack()). I > > > > don't think this ever actually worked for the main thread stack, but it > > > > now also blocks expansion as the default stack size of 8 MiB is smaller > > > > than the stack gap of 16 MiB. Would it make sense to skip over > > > > PROT_NONE mappings when checking whether it's safe to expand? > > > > This is what my workaround for the older patch was doing, actually. We > > have deployed that as a follow up fix on our older code bases. And this > > has fixed verious issues with Java which was doing the similar thing. > > Here is a forward port (on top of the current Linus tree) of my earlier > patch. I have dropped a note about java stack trace because this would > most likely be not the case with the Hugh's patch. The problem is the > same in principle though. Note I didn't get to test this properly yet > but it should be pretty much obvious. Tested with the attached program. root@test1:~# ./stack_crash Stack top:0x7fffcdb605ec mmap:0x7fffcc760000 address:0x7fffcc760ff8 aligned:0x7fffcc760000 mapped:[7fffcc760000,7fffcc761000] diff:-8 [...] so we faulted on the PROT_NONE while with #define MAPING_PROT PROT_READ root@test1:~# ./stack_crash Stack top:0x7ffe73dde6fc mmap:0x7ffe729de000 address:0x7ffe72adefd8 aligned:0x7ffe72ade000 mapped:[7ffe729de000,7ffe729df000] diff:1048536 [...] we failed 1MB ahead of the mapping. -- Michal Hocko SUSE Labs