From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752043AbeCNSzZ (ORCPT ); Wed, 14 Mar 2018 14:55:25 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56342 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751700AbeCNSzV (ORCPT ); Wed, 14 Mar 2018 14:55:21 -0400 Date: Wed, 14 Mar 2018 11:54:52 -0700 From: Ram Pai To: Dave Hansen Cc: mingo@redhat.com, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, benh@kernel.crashing.org, paulus@samba.org, khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, ebiederm@xmission.com, corbet@lwn.net, arnd@arndb.de, fweimer@redhat.com, msuchanek@suse.com Subject: Re: [PATCH 1/1 v2] x86: pkey-mprotect must allow pkey-0 Reply-To: Ram Pai References: <1521013574-27041-1-git-send-email-linuxram@us.ibm.com> <18b155e3-07e9-5a4b-1f95-e1667078438c@intel.com> <20180314171448.GA1060@ram.oc3035372033.ibm.com> <5027ca9e-63c8-47ab-960d-a9c4466d7075@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5027ca9e-63c8-47ab-960d-a9c4466d7075@intel.com> User-Agent: Mutt/1.5.20 (2009-12-10) X-TM-AS-GCONF: 00 x-cbid: 18031418-0040-0000-0000-000004208106 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18031418-0041-0000-0000-00002623869A Message-Id: <20180314185452.GB1060@ram.oc3035372033.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-14_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803140206 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 14, 2018 at 10:51:26AM -0700, Dave Hansen wrote: > On 03/14/2018 10:14 AM, Ram Pai wrote: > > I look at key-0 as 'the key'. It has special status. > > (a) It always exist. > > Do you mean "is always allocated"? always allocated and cannot be freed. Hence always exists. If we let it freed, than yes 'it is always allocated', but may not 'always exist'. > > > (b) it cannot be freed. > > This is the one I'm questioning. this is a philosophical question. Should we allow the application shoot-its-own-feet or help it from doing so. I tend to gravitate towards the later. > > > (c) it is assigned by default. > > I agree on this totally. :) good. we have some common ground :) > > > (d) its permissions cannot be modified. > > Why not? You could pretty easily get a thread going that had its stack > covered with another pkey and that was being very careful what it > accesses. It could pretty easily set pkey-0's access or write-disable bits. ok. I see your point. Will not argue against it. > > > (e) it bypasses key-permission checks when assigned. > > I don't think this is necessary. I think the only rule we *need* is: > > pkey-0 is allocated implicitly at execve() time. You do not > need to call pkey_alloc() to allocate it. And can be explicitly associated with any address range ? > > > An arch need not necessarily map 'the key-0' to its key-0. It could > > internally map it to any of its internal key of its choice, transparent > > to the application. > > I don't understand what you are saying here. I was trying to disassociate the notion that "application's key-0 means hardware's key-0". Nevermind. its not important for this discussion. -- Ram Pai