From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 4F8AB6B02B4 for ; Wed, 22 Nov 2017 11:32:15 -0500 (EST) Received: by mail-pf0-f199.google.com with SMTP id c83so14959897pfj.11 for ; Wed, 22 Nov 2017 08:32:15 -0800 (PST) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTPS id j3si9356265pff.89.2017.11.22.08.32.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Nov 2017 08:32:14 -0800 (PST) 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> <9ec19ff3-86f6-7cfe-1a07-1ab1c5d9882c@redhat.com> From: Dave Hansen Message-ID: Date: Wed, 22 Nov 2017 08:32:11 -0800 MIME-Version: 1.0 In-Reply-To: <9ec19ff3-86f6-7cfe-1a07-1ab1c5d9882c@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Florian Weimer , Vlastimil Babka , linux-x86_64@vger.kernel.org, linux-arch@vger.kernel.org Cc: linux-mm , Linux API On 11/22/2017 08:21 AM, Florian Weimer wrote: > 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 a??MPK is not supporteda??, 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. No, the default is clearly 0 and documented to be so. The PROT_EXEC emulation one should be inaccessible in all the APIs so does not even show up as *being* a key in the API. The fact that it's implemented with pkeys should be pretty immaterial other than the fact that you can't touch the high bits in PKRU. -- 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