From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751365AbdKTWvE (ORCPT ); Mon, 20 Nov 2017 17:51:04 -0500 Received: from mail-ot0-f193.google.com ([74.125.82.193]:38359 "EHLO mail-ot0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751159AbdKTWvC (ORCPT ); Mon, 20 Nov 2017 17:51:02 -0500 X-Google-Smtp-Source: AGs4zMb5kmpjZ1B1hKW1DJxmUSB7p63VBejQrvvUZ7B5Pi5ZKDbieWTI+4DGKjR3Xl6nDxtfd6gJpw== Subject: Re: [PATCH 00/18] arm64: Unmap the kernel whilst running in userspace (KAISER) To: Will Deacon , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, ard.biesheuvel@linaro.org, sboyd@codeaurora.org, dave.hansen@linux.intel.com, keescook@chromium.org References: <1510942921-12564-1-git-send-email-will.deacon@arm.com> From: Laura Abbott Message-ID: Date: Mon, 20 Nov 2017 14:50:58 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <1510942921-12564-1-git-send-email-will.deacon@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/17/2017 10:21 AM, Will Deacon wrote: > Hi all, > > This patch series implements something along the lines of KAISER for arm64: > > https://gruss.cc/files/kaiser.pdf > > although I wrote this from scratch because the paper has some funny > assumptions about how the architecture works. There is a patch series > in review for x86, which follows a similar approach: > > http://lkml.kernel.org/r/<20171110193058.BECA7D88@viggo.jf.intel.com> > > and the topic was recently covered by LWN (currently subscriber-only): > > https://lwn.net/Articles/738975/ > > The basic idea is that transitions to and from userspace are proxied > through a trampoline page which is mapped into a separate page table and > can switch the full kernel mapping in and out on exception entry and > exit respectively. This is a valuable defence against various KASLR and > timing attacks, particularly as the trampoline page is at a fixed virtual > address and therefore the kernel text can be randomized independently. > > The major consequences of the trampoline are: > > * We can no longer make use of global mappings for kernel space, so > each task is assigned two ASIDs: one for user mappings and one for > kernel mappings > > * Our ASID moves into TTBR1 so that we can quickly switch between the > trampoline and kernel page tables > > * Switching TTBR0 always requires use of the zero page, so we can > dispense with some of our errata workaround code. > > * entry.S gets more complicated to read > > The performance hit from this series isn't as bad as I feared: things > like cyclictest and kernbench seem to be largely unaffected, although > syscall micro-benchmarks appear to show that syscall overhead is roughly > doubled, and this has an impact on things like hackbench which exhibits > a ~10% hit due to its heavy context-switching. > > Patches based on 4.14 and also pushed here: > > git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git kaiser > > Feedback welcome, > > Will > Passed some basic tests on Hikey Android and my Mustang box. I'll leave the Mustang building kernels for a few days. You're welcome to add Tested-by or I can re-test on v2. Thanks, Laura