Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755444AbeAHSWy (ORCPT + 1 other); Mon, 8 Jan 2018 13:22:54 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:35942 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755000AbeAHSWv (ORCPT ); Mon, 8 Jan 2018 13:22:51 -0500 Date: Mon, 8 Jan 2018 18:22:20 +0000 From: Alan Cox To: Will Deacon Cc: Jayachandran C , Marc Zyngier , linux-arm-kernel@lists.infradead.org, lorenzo.pieralisi@arm.com, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, labbott@redhat.com, christoffer.dall@linaro.org Subject: Re: [v2,03/11] arm64: Take into account ID_AA64PFR0_EL1.CSV3 Message-ID: <20180108182220.34233ebc@alans-desktop> In-Reply-To: <20180108175100.GW25869@arm.com> References: <1515157961-20963-4-git-send-email-will.deacon@arm.com> <20180108072253.GA178830@jc-sabre> <9bc1f137-d78c-e46e-e1bc-f49160d5f289@arm.com> <20180108174016.GB180149@jc-sabre> <20180108175100.GW25869@arm.com> Organization: Intel Corporation X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: > > On systems that are not vulnerable to variant 3, this is an unnecessary > > overhead. > > KASLR can be bypassed on CPUs that are not vulnerable to variant 3 simply > by timing how long accesses to kernel addresses from EL0 take -- please read > the original KAISER paper for details about that attack on x86. kpti > mitigates that. If you don't care about KASLR, don't enable it (arguably > it's useless without kpti). KASLR is primarily of value for remote protection. Alan