From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Weimer Subject: Re: MPK: removing a pkey Date: Wed, 22 Nov 2017 17:21:31 +0100 Message-ID: <9ec19ff3-86f6-7cfe-1a07-1ab1c5d9882c@redhat.com> References: <0f006ef4-a7b5-c0cf-5f58-d0fd1f911a54@redhat.com> <8741e4d6-6ac0-9c07-99f3-95d8d04940b4@suse.cz> <813f9736-36dd-b2e5-c850-9f2d5f94514a@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Content-Language: en-US Sender: owner-linux-mm@kvack.org To: Dave Hansen , Vlastimil Babka , linux-x86_64@vger.kernel.org, linux-arch@vger.kernel.org Cc: linux-mm , Linux API List-Id: linux-arch.vger.kernel.org On 11/22/2017 05:10 PM, Dave Hansen wrote: > On 11/22/2017 04:15 AM, Florian Weimer wrote: >> On 11/22/2017 09:18 AM, Vlastimil Babka wrote: >>> And, was the pkey == -1 internal wiring supposed to be exposed to the >>> pkey_mprotect() signal, or should there have been a pre-check returning >>> EINVAL in SYSCALL_DEFINE4(pkey_mprotect), before calling >>> do_mprotect_pkey())? I assume it's too late to change it now anyway (or >>> not?), so should we also document it? >> >> I think the -1 case to the set the default key is useful because it >> allows you to use a key value of -1 to mean “MPK is not supported”, and >> still call pkey_mprotect. > > The behavior to not allow 0 to be set was unintentional and is a bug. > We should fix that. On the other hand, x86-64 has no single default protection key due to the PROT_EXEC emulation. Florian -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:50816 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751303AbdKVQVf (ORCPT ); Wed, 22 Nov 2017 11:21:35 -0500 Subject: Re: MPK: removing a pkey References: <0f006ef4-a7b5-c0cf-5f58-d0fd1f911a54@redhat.com> <8741e4d6-6ac0-9c07-99f3-95d8d04940b4@suse.cz> <813f9736-36dd-b2e5-c850-9f2d5f94514a@redhat.com> From: Florian Weimer Message-ID: <9ec19ff3-86f6-7cfe-1a07-1ab1c5d9882c@redhat.com> Date: Wed, 22 Nov 2017 17:21:31 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Hansen , Vlastimil Babka , linux-x86_64@vger.kernel.org, linux-arch@vger.kernel.org Cc: linux-mm , Linux API Message-ID: <20171122162131.9H1aDr1cAyi4V_uAfjRkTvV76h-P3r6bQFul98JG_cw@z> On 11/22/2017 05:10 PM, Dave Hansen wrote: > On 11/22/2017 04:15 AM, Florian Weimer wrote: >> On 11/22/2017 09:18 AM, Vlastimil Babka wrote: >>> And, was the pkey == -1 internal wiring supposed to be exposed to the >>> pkey_mprotect() signal, or should there have been a pre-check returning >>> EINVAL in SYSCALL_DEFINE4(pkey_mprotect), before calling >>> do_mprotect_pkey())? I assume it's too late to change it now anyway (or >>> not?), so should we also document it? >> >> I think the -1 case to the set the default key is useful because it >> allows you to use a key value of -1 to mean “MPK is not supported”, and >> still call pkey_mprotect. > > The behavior to not allow 0 to be set was unintentional and is a bug. > We should fix that. On the other hand, x86-64 has no single default protection key due to the PROT_EXEC emulation. Florian