From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752532AbeC0C1b (ORCPT ); Mon, 26 Mar 2018 22:27:31 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:33302 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752480AbeC0C1a (ORCPT ); Mon, 26 Mar 2018 22:27:30 -0400 Date: Mon, 26 Mar 2018 19:27:18 -0700 From: Ram Pai To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, tglx@linutronix.de, dave.hansen@intel.com, mpe@ellerman.id.au, mingo@kernel.org, akpm@linux-foundation.org, shuah@kernel.org Subject: Re: [PATCH 1/9] x86, pkeys: do not special case protection key 0 Reply-To: Ram Pai References: <20180323180903.33B17168@viggo.jf.intel.com> <20180323180905.B40984E6@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180323180905.B40984E6@viggo.jf.intel.com> User-Agent: Mutt/1.5.20 (2009-12-10) X-TM-AS-GCONF: 00 x-cbid: 18032702-0012-0000-0000-000005C3936B X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18032702-0013-0000-0000-0000193FCB90 Message-Id: <20180327022718.GD5743@ram.oc3035372033.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-27_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 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-1803270024 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 23, 2018 at 11:09:05AM -0700, Dave Hansen wrote: > > From: Dave Hansen > > mm_pkey_is_allocated() treats pkey 0 as unallocated. That is > inconsistent with the manpages, and also inconsistent with > mm->context.pkey_allocation_map. Stop special casing it and only > disallow values that are actually bad (< 0). > > The end-user visible effect of this is that you can now use > mprotect_pkey() to set pkey=0. > > This is a bit nicer than what Ram proposed because it is simpler > and removes special-casing for pkey 0. On the other hand, it does > allow applciations to pkey_free() pkey-0, but that's just a silly > thing to do, so we are not going to protect against it. The more I think about this, the more I feel we are opening up a can of worms. I am ok with a bad application, shooting itself in its feet. But I am worried about all the bug reports and support requests we will encounter when applications inadvertently shoot themselves and blame it on the kernel. a warning in dmesg logs indicating a free-of-pkey-0 can help deflect the blame from the kernel. RP