From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 401PKr4CBbzDqsV for ; Wed, 14 Mar 2018 19:00:47 +1100 (AEDT) Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0 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 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 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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