From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752947AbaJKKfU (ORCPT ); Sat, 11 Oct 2014 06:35:20 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48954 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752851AbaJKKfQ (ORCPT ); Sat, 11 Oct 2014 06:35:16 -0400 Message-ID: <543907B5.7060001@zytor.com> Date: Sat, 11 Oct 2014 03:34:29 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.1 MIME-Version: 1.0 To: Baoquan He , Vivek Goyal , Kees Cook CC: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, keescook@chromium.org, ak@linux.intel.com, ebiederm@xmission.com, kexec@lists.infradead.org, whissi@whissi.de, kumagai-atsushi@mxc.nes.nec.co.jp, stable@vger.kernel.org Subject: Re: [resend Patch v3 1/2] kaslr: check if kernel location is changed References: <1412060896-1902-1-git-send-email-bhe@redhat.com> <542B1EC1.8090502@zytor.com> <20141001135237.GA13689@redhat.com> <543553C7.9010906@zytor.com> <20141008192728.GA26517@redhat.com> <20141011031452.GB11560@dhcp-16-116.nay.redhat.com> In-Reply-To: <20141011031452.GB11560@dhcp-16-116.nay.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/10/2014 08:14 PM, Baoquan He wrote: > On 10/08/14 at 03:27pm, Vivek Goyal wrote: >> On Wed, Oct 08, 2014 at 08:09:59AM -0700, H. Peter Anvin wrote: > >>> Sorry... this makes no sense. >>> >>> For x86-64, there is no direct connection between the physical and >>> virtual address spaces that the kernel runs in... >> >> I am sorry I did not understand this one. I thought that initial >> relocatable kernel implementaion did not have any direct connection >> between virtual and physical address. One could load kernel anywhere >> and kernel virtual address will not change and we will just adjust >> page tables to map virtual address to right physical address. >> >> Now handle_relocation() stuff seems to introduce a close coupling >> between physical and virtual address. So if kernel shifts by 16MB >> in physical address space, then it will shift by equal amount >> in virtual address space. So there seems to be a direct connection >> between virtual and physical address space in this case. > > Yeah, it's exactly as Vivek said. > > Before kaslr was introduced, x86_64 kernel can be put anywhere, and > always _text is 0xffffffff81000000. Meanwhile phys_base contains the > offset between the compiled addr (namely 0x1000000) and kernel loaded > addr. After kaslr implementation was added, as long as kernel loaded > addr is different 0x1000000, it will call handle_relocations(). The > offset now is added onto each symbols including _text and phys_base > becomes 0. > > It's clearly showing that by checking /proc/kallsyms and value of > phys_base. > This really shouldn't have happened this way on x86-64. It has to happen this way on i386, but I worry that this may be a serious misdesign in kaslr on x86-64. I'm also wondering if there is any other fallout of this? -hpa