From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f199.google.com (mail-qk0-f199.google.com [209.85.220.199]) by kanga.kvack.org (Postfix) with ESMTP id 8F6C86B0005 for ; Wed, 14 Mar 2018 04:00:46 -0400 (EDT) Received: by mail-qk0-f199.google.com with SMTP id g199so1573104qke.18 for ; Wed, 14 Mar 2018 01:00:46 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id g5si1754420qkc.463.2018.03.14.01.00.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Mar 2018 01:00:45 -0700 (PDT) Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0 References: <1520583161-11741-1-git-send-email-linuxram@us.ibm.com> <20180309200017.GR1060@ram.oc3035372033.ibm.com> From: Florian Weimer Message-ID: Date: Wed, 14 Mar 2018 09:00:36 +0100 MIME-Version: 1.0 In-Reply-To: <20180309200017.GR1060@ram.oc3035372033.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ram Pai Cc: mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, 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, msuchanek@suse.com, Ulrich.Weigand@de.ibm.com On 03/09/2018 09:00 PM, Ram Pai wrote: > On Fri, Mar 09, 2018 at 12:04:49PM +0100, Florian Weimer wrote: >> On 03/09/2018 09:12 AM, Ram Pai wrote: >>> Once an address range is associated with an allocated pkey, it cannot be >>> reverted back to key-0. There is no valid reason for the above behavior. >> >> mprotect without a key does not necessarily use key 0, e.g. if >> protection keys are used to emulate page protection flag combination >> which is not directly supported by the hardware. >> >> Therefore, it seems to me that filtering out non-allocated keys is >> the right thing to do. > > I am not sure, what you mean. Do you agree with the patch or otherwise? I think it's inconsistent to make key 0 allocated, but not the key which is used for PROT_EXEC emulation, which is still reserved. Even if you change the key 0 behavior, it is still not possible to emulate mprotect behavior faithfully with an allocated key. Thanks, Florian