Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965358AbeAKSFA (ORCPT + 1 other); Thu, 11 Jan 2018 13:05:00 -0500 Received: from mail-vk0-f68.google.com ([209.85.213.68]:46638 "EHLO mail-vk0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965083AbeAKSE6 (ORCPT ); Thu, 11 Jan 2018 13:04:58 -0500 X-Google-Smtp-Source: ACJfBottpIenECKzHUYYiLXfptuNBvof5B/DquJ5CyI7FodX45yZn8O7W5A9hEepfGm70d7PKNzx+vcbgHCm14wDewQ= MIME-Version: 1.0 In-Reply-To: <20180111090006.GA9648@localhost.localdomain> References: <20180104080219.23893-1-fanc.fnst@cn.fujitsu.com> <20180104080219.23893-2-fanc.fnst@cn.fujitsu.com> <20180104103057.GC7235@x1> <20180104112104.67b88e2d@redhat.com> <20180111090006.GA9648@localhost.localdomain> From: Kees Cook Date: Thu, 11 Jan 2018 10:04:56 -0800 X-Google-Sender-Auth: acV4mOI83bMdW4xKZQ9yuD7Tn9c Message-ID: Subject: Re: KASLR may break some kernel features (was Re: [PATCH v5 1/4] kaslr: add immovable_mem=nn[KMG]@ss[KMG] to specify extracting memory) To: Baoquan He Cc: Luiz Capitulino , Chao Fan , LKML , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , yasu.isimatu@gmail.com, indou.takao@jp.fujitsu.com, caoj.fnst@cn.fujitsu.com, Dou Liyang Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Thu, Jan 11, 2018 at 1:00 AM, Baoquan He wrote: > Hi Luiz, > > On 01/04/18 at 11:21am, Luiz Capitulino wrote: >> Having a generic kaslr parameter to control where the kernel is extracted >> is one solution for this problem. >> >> The general problem statement is that KASLR may break some kernel features >> depending on where the kernel is extracted. Two examples are hot-plugged >> memory (this series) and 1GB HugeTLB pages. >> >> The 1GB HugeTLB page issue is not specific to KVM guests. It just happens >> that there's a bunch of people running guests with up to 5GB of memory and >> with that amount of memory you have one or two 1GB pages and is easier for >> KASLR to extract the kernel into a 1GB region and split a 1GB page. So, >> you may not get any 1GB pages at all when this happens. However, I can also >> reproduce this on bare-metal with lots of memory where I can loose a 1GB >> page from time to time. >> >> Having a kaslr_range= parameter solves both issues, but two major drawbacks >> is that it breaks existing setups and I guess users will have a very hard >> time choosing good ranges. >> >> Another idea would be to have a CONFIG_KASLR_RANGES, where each arch >> could have a list of ranges known to contain holes and/or immovable >> memory and only extract the kernel into those ranges. > > If add CONFIG_KASLR_RANGES, then a distro like RHEL will have this range > always, whether people need hugetlb or not. > > So in this case, what range do we need to avoid? Only [1G, 2G]? Any ranges like that that need to be avoided should be known at build time, so they should simply be added to the mem_avoid list that is already present in the KASLR code... -Kees -- Kees Cook Pixel Security