From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947007Ab3BHUSz (ORCPT ); Fri, 8 Feb 2013 15:18:55 -0500 Received: from terminus.zytor.com ([198.137.202.10]:36312 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964780Ab3BHUSv (ORCPT ); Fri, 8 Feb 2013 15:18:51 -0500 User-Agent: K-9 Mail for Android In-Reply-To: References: <20130208191213.GA25081@www.outflux.net> <00780235-deac-4f80-b936-867834e05661@email.android.com> <5115553A.5000708@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [PATCH] x86: Lock down MSR writing in secure boot From: "H. Peter Anvin" Date: Fri, 08 Feb 2013 12:18:27 -0800 To: Kees Cook CC: LKML , Matthew Garrett , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , "linux-efi@vger.kernel.org" , linux-security-module Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Analogy fail. The /dev/mem lockout applies to system RAM, not MMIO. I fear COMPROMISE_KERNEL is becoming the new SYS_ADMIN, which in turn is the new root. Why? Because it is inhebtly about a usage model, not about a specific resource. Kees Cook wrote: >On Fri, Feb 8, 2013 at 11:42 AM, H. Peter Anvin wrote: >> On 02/08/2013 11:18 AM, Kees Cook wrote: >>> >>> No. CAP_RAWIO is for reading. Writing needs a much stronger check. >> >> If so, I suspect we need to do this for *all* raw I/O... but I keep >> wondering how much more sensitive writing really is than reading. > >Well, I think there's a reasonable distinction between systems that >expect to strictly enforce user-space/kernel-space separation >(CAP_COMPROMISE_KERNEL) and things that are fiddling with hardware >(CAP_SYS_RAWIO). > >For example, even things like /dev/mem already have this separation >(although it is stronger). You can't open /dev/mem without >CAP_SYS_RAWIO, but if you do, you still can't write to RAM in >/dev/mem. This might be one of the earliest examples of this >distinction, actually. > >I think it's likely that after a while, we can convert some of these >proposed CAP_COMPROMISE_KERNEL checks in always-deny once we figure >out how to deal with those areas more safely. > >-Kees > >-- >Kees Cook >Chrome OS Security -- Sent from my mobile phone. Please excuse brevity and lack of formatting.