From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754489AbaJMPny (ORCPT ); Mon, 13 Oct 2014 11:43:54 -0400 Received: from terminus.zytor.com ([198.137.202.10]:42024 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754432AbaJMPnx (ORCPT ); Mon, 13 Oct 2014 11:43:53 -0400 Message-ID: <543BF304.9090708@zytor.com> Date: Mon, 13 Oct 2014 08:43:00 -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: Vivek Goyal CC: Baoquan He , Kees Cook , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, x86@kernel.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> <543907B5.7060001@zytor.com> <20141013125257.GB6466@redhat.com> <20141013151955.GA9777@redhat.com> In-Reply-To: <20141013151955.GA9777@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/13/2014 08:19 AM, Vivek Goyal wrote: >>> >>> 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? >> >> I agree. On x86_64, we should stick to previous design and this new >> logic of performing relocations does not sound very clean and makes >> things very confusing. >> >> I am wondering that why couldn't we simply adjust page tables in case of >> kaslr on x86_64, instead of performing relocations. > > Well, IIUC, if virtual addresses are shifted w.r.t what virtual address > kernel was compiled for, then relocation will have to be done. > > So question will be if physical address shift is enough for kaslr or > virtual address shift is necessary. > I would assume that without a virtual address shift kaslr is pretty darn pointless. Without the physical address shift the 1:1 map can be used, and again, kaslr becomes pointless. However, there is absolutely no reason why they should be coupled. They can, in fact, be independently randomized. -hpa