From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D12DC63777 for ; Tue, 1 Dec 2020 02:56:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D80F22085B for ; Tue, 1 Dec 2020 02:56:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727030AbgLAC4O convert rfc822-to-8bit (ORCPT ); Mon, 30 Nov 2020 21:56:14 -0500 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:54458 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725900AbgLAC4N (ORCPT ); Mon, 30 Nov 2020 21:56:13 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=rongwei.wang@linux.alibaba.com;NM=1;PH=DS;RN=16;SR=0;TI=SMTPD_---0UH5AeAb_1606791329; Received: from 30.225.32.58(mailfrom:rongwei.wang@linux.alibaba.com fp:SMTPD_---0UH5AeAb_1606791329) by smtp.aliyun-inc.com(127.0.0.1); Tue, 01 Dec 2020 10:55:30 +0800 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.4\)) Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver From: wangrongwei In-Reply-To: <20201130175706.GA25457@willie-the-truck> Date: Tue, 1 Dec 2020 10:55:29 +0800 Cc: catalin.marinas@arm.com, bjorn.andersson@linaro.org, shawnguo@kernel.org, vkoul@kernel.org, geert+renesas@glider.be, Anson.Huang@nxp.com, michael@walle.cc, krzk@kernel.org, olof@lixom.net, vincenzo.frascino@arm.com, ardb@kernel.org, masahiroy@kernel.org, gshan@redhat.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: References: <20201130174833.41315-1-rongwei.wang@linux.alibaba.com> <20201130175706.GA25457@willie-the-truck> To: Will Deacon X-Mailer: Apple Mail (2.3608.120.23.2.4) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Will Thanks for your reply! There are absolutely privileged registers, and seriously expose the interface directly! However, these interfaces (/dev/cpu//msr) need permissions to access, so there should be few security issues. In addition, it may be due to my unclear description above. This driver is mainly a debugging tool. It make developers can easily get the values of some system registers without modifying the kernel. In fact, we first considered the /dev/mem solution, but it seems that /dev/mem can map peripheral or IO registers, but not system registers. > 2020年12月1日 上午1:57，Will Deacon 写道： > > On Tue, Dec 01, 2020 at 01:48:30AM +0800, Rongwei Wang wrote: >> MSR ARM driver aims to provide interfacs for user to read or write data to all >> system registers. Its functions is same as MSR driver (x86 platform). It mainly >> depends on kprobe and undef exception to read or write system registers >> dynamicly. > > ... but why? These are privileged registers for a reason, and giving > userspace access to them is bound to cause serious problems. Why can't we > do whatever it is that userspace is trying to do by poking these things in > the kernel instead? This interface is a bit like using /dev/mem instead of > writing a proper device driver. > > Thanks, > > Will