From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754027AbdFWIqZ (ORCPT ); Fri, 23 Jun 2017 04:46:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:38538 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753713AbdFWIqX (ORCPT ); Fri, 23 Jun 2017 04:46:23 -0400 Date: Fri, 23 Jun 2017 10:46:19 +0200 From: Michal Hocko To: Thomas Gleixner , Ingo Molnar Cc: Jiri Kosina , Andi Kleen , "H. Peter Anvin" , LKML , linux-mm@kvack.org, x86@kernel.org Subject: Re: [RFC PATCH] mmap, aslr: do not enforce legacy mmap on unlimited stacks Message-ID: <20170623084619.GI5308@dhcp22.suse.cz> References: <20170614082218.12450-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170614082218.12450-1-mhocko@kernel.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 ping? On Wed 14-06-17 10:22:18, Michal Hocko wrote: > From: Michal Hocko > > Since cc503c1b43e0 ("x86: PIE executable randomization") we treat > applications with RLIMIT_STACK configured to unlimited as legacy > and so we a) set the mmap_base to 1/3 of address space + randomization > and b) mmap from bottom to top. This makes some sense as it allows the > stack to grow really large. On the other hand it reduces the address > space usable for default mmaps (wihout address hint) quite a lot. We > have received a bug report that SAP HANA workload has hit into this > limitation. > > We could argue that the user just got what he asked for when setting > up the unlimited stack but to be realistic growing stack up to 1/6 > TASK_SIZE (allowed by mmap_base) is pretty much unimited in the real > life. This would give mmap 20TB of additional address space which is > quite nice. Especially when it is much more likely to use that address > space than the reserved stack. > > Digging into the history the original implementation of the > randomization 8817210d4d96 ("[PATCH] x86_64: Flexmap for 32bit and > randomized mappings for 64bit") didn't have this restriction. > > Signed-off-by: Michal Hocko > --- > > Hi, > I am sending this as a RFC because I am not really sure how to deal with > this. We might as well ignore the reported issue and claim "do not use > unlimited stacks" and be done with it. I just stroke me as an unexpected > behavior. > > arch/x86/mm/mmap.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c > index 19ad095b41df..797295e792b2 100644 > --- a/arch/x86/mm/mmap.c > +++ b/arch/x86/mm/mmap.c > @@ -74,9 +74,6 @@ static int mmap_is_legacy(void) > if (current->personality & ADDR_COMPAT_LAYOUT) > return 1; > > - if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) > - return 1; > - > return sysctl_legacy_va_layout; > } > > -- > 2.11.0 > -- Michal Hocko SUSE Labs