From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: [PATCH 5/8] x86, pkeys: allocation/free syscalls Date: Thu, 2 Jun 2016 19:26:03 -0500 Message-ID: <5499ff55-ae0f-e54c-05fd-b1e76dc05a89@gmail.com> References: <20160531152814.36E0B9EE@viggo.jf.intel.com> <20160531152822.FE8D405E@viggo.jf.intel.com> <20160601123705.72a606e7@lwn.net> <574F386A.8070106@sr71.net> <574F7B16.4080906@sr71.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <574F7B16.4080906-gkUM19QKKo4@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dave Hansen Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Jonathan Corbet , lkml , "x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , Linux API , linux-arch , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , Linus Torvalds , Andrew Morton , Dave Hansen List-Id: linux-arch.vger.kernel.org On 06/01/2016 07:17 PM, Dave Hansen wrote: > On 06/01/2016 05:11 PM, Michael Kerrisk (man-pages) wrote: >>>>>> >>>>>> If I read this right, it doesn't actually remove any pkey restrictions >>>>>> that may have been applied while the key was allocated. So there could be >>>>>> pages with that key assigned that might do surprising things if the key is >>>>>> reallocated for another use later, right? Is that how the API is intended >>>>>> to work? >>>> >>>> Yeah, that's how it works. >>>> >>>> It's not ideal. It would be _best_ if we during mm_pkey_free(), we >>>> ensured that no VMAs under that mm have that vma_pkey() set. But, that >>>> search would be potentially expensive (a walk over all VMAs), or would >>>> force us to keep a data structure with a count of all the VMAs with a >>>> given key. >>>> >>>> I should probably discuss this behavior in the manpages and address it >> s/probably// >> >> And, did I miss it. Was there an updated man-pages patch in the latest >> series? I did not notice it. > > There have been to changes to the patches that warranted updating the > manpages until now. I'll send the update immediately. Do those updated pages include discussion of the point noted above? I could not see it mentioned there. Just by the way, the above behavior seems to offer possibilities for users to shoot themselves in the foot, in a way that has security implications. (Or do I misunderstand?) Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f65.google.com ([209.85.213.65]:35586 "EHLO mail-vk0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932143AbcFCA0X (ORCPT ); Thu, 2 Jun 2016 20:26:23 -0400 Subject: Re: [PATCH 5/8] x86, pkeys: allocation/free syscalls References: <20160531152814.36E0B9EE@viggo.jf.intel.com> <20160531152822.FE8D405E@viggo.jf.intel.com> <20160601123705.72a606e7@lwn.net> <574F386A.8070106@sr71.net> <574F7B16.4080906@sr71.net> From: "Michael Kerrisk (man-pages)" Message-ID: <5499ff55-ae0f-e54c-05fd-b1e76dc05a89@gmail.com> Date: Thu, 2 Jun 2016 19:26:03 -0500 MIME-Version: 1.0 In-Reply-To: <574F7B16.4080906@sr71.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Hansen Cc: mtk.manpages@gmail.com, Jonathan Corbet , lkml , "x86@kernel.org" , Linux API , linux-arch , "linux-mm@kvack.org" , Linus Torvalds , Andrew Morton , Dave Hansen Message-ID: <20160603002603.xsCWgEnF2u_01Ktqon1k8Kk1DsnoZ5bckm50SlOZ-x8@z> On 06/01/2016 07:17 PM, Dave Hansen wrote: > On 06/01/2016 05:11 PM, Michael Kerrisk (man-pages) wrote: >>>>>> >>>>>> If I read this right, it doesn't actually remove any pkey restrictions >>>>>> that may have been applied while the key was allocated. So there could be >>>>>> pages with that key assigned that might do surprising things if the key is >>>>>> reallocated for another use later, right? Is that how the API is intended >>>>>> to work? >>>> >>>> Yeah, that's how it works. >>>> >>>> It's not ideal. It would be _best_ if we during mm_pkey_free(), we >>>> ensured that no VMAs under that mm have that vma_pkey() set. But, that >>>> search would be potentially expensive (a walk over all VMAs), or would >>>> force us to keep a data structure with a count of all the VMAs with a >>>> given key. >>>> >>>> I should probably discuss this behavior in the manpages and address it >> s/probably// >> >> And, did I miss it. Was there an updated man-pages patch in the latest >> series? I did not notice it. > > There have been to changes to the patches that warranted updating the > manpages until now. I'll send the update immediately. Do those updated pages include discussion of the point noted above? I could not see it mentioned there. Just by the way, the above behavior seems to offer possibilities for users to shoot themselves in the foot, in a way that has security implications. (Or do I misunderstand?) Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/