Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752695AbbLNPcF (ORCPT ); Mon, 14 Dec 2015 10:32:05 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:43489 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbbLNPcE (ORCPT ); Mon, 14 Dec 2015 10:32:04 -0500 Date: Mon, 14 Dec 2015 16:32:34 +0100 From: Quentin Casasnovas To: Cyrill Gorcunov Cc: Quentin Casasnovas , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vegard Nossum , Linus Torvalds , Willy Tarreau , Andy Lutomirski , Kees Cook , Vladimir Davydov , Konstantin Khlebnikov , Pavel Emelyanov , Peter Zijlstra Subject: Re: [RFC 1/2] [RFC] mm: Account anon mappings as RLIMIT_DATA Message-ID: <20151214153234.GE3604@chrystal.uk.oracle.com> References: <20151213201646.839778758@gmail.com> <20151214145126.GC3604@chrystal.uk.oracle.com> <20151214151116.GE14045@uranus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151214151116.GE14045@uranus> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1980 Lines: 44 On Mon, Dec 14, 2015 at 06:11:16PM +0300, Cyrill Gorcunov wrote: > On Mon, Dec 14, 2015 at 03:51:26PM +0100, Quentin Casasnovas wrote: > ... > > > > Do we want to fold may_expand_anon_vm() into may_expand_vm() (potentially > > passing it the flags/struct file if needed) so there is just one such > > helper function? Rationale being that it then gets hard to see what > > restricts what, and it's easy to miss one place. > > I tried to make the patch small as possible (because otherwise indeed > I would have to pass @vm_file|@file as additional argument). This won't > be a problem but may_expand_vm is called way more times than > may_expand_anon_vm. That's the only rationale I followed. > > > For example, I couldn't find anything preventing a user to > > mmap(MAP_GROWSDOWN) and uses that as a base to get pages that would not be > > accounted for in your patch (making it a poor-man mremap()). > > growsup/down stand for stack usage iirc, so it was intentionally > not accounted here. > Right, but in the same vein of Linus saying RLIMIT_DATA is/was useless because everyone could use mmap() instead of brk() to get anonymous memory, what's the point of restricting "almost-all" anonymous memory if one can just use MAP_GROWSDOWN/UP and cause repeated page faults to extend that mapping, circumventing your checks? That makes the new restriction as useless as what RLIMIT_DATA used to be, doesn't it? > > > > I only had a quick look so apologies if this is handled and I missed it :) > > thanks for feedback! also take a look on Kostya's patch, I think it's > even better approach (and I like it more than mine). Ha I'm not subscribed to LKML so I missed those, I suppose you can ignore my comments then! :) Quentin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/