From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f176.google.com (mail-io0-f176.google.com [209.85.223.176]) by kanga.kvack.org (Postfix) with ESMTP id 56F0C82F7F for ; Thu, 24 Sep 2015 15:10:06 -0400 (EDT) Received: by ioiz6 with SMTP id z6so87315038ioi.2 for ; Thu, 24 Sep 2015 12:10:06 -0700 (PDT) Received: from blackbird.sr71.net (www.sr71.net. [198.145.64.142]) by mx.google.com with ESMTP id f6si5491711igg.72.2015.09.24.12.10.04 for ; Thu, 24 Sep 2015 12:10:04 -0700 (PDT) Subject: Re: [PATCH 26/26] x86, pkeys: Documentation References: <20150916174903.E112E464@viggo.jf.intel.com> <20150916174913.AF5FEA6D@viggo.jf.intel.com> <20150920085554.GA21906@gmail.com> <55FF88BA.6080006@sr71.net> <20150924094956.GA30349@gmail.com> From: Dave Hansen Message-ID: <56044A88.7030203@sr71.net> Date: Thu, 24 Sep 2015 12:10:00 -0700 MIME-Version: 1.0 In-Reply-To: <20150924094956.GA30349@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andrew Morton , Peter Zijlstra , Andy Lutomirski , Borislav Petkov , Kees Cook On 09/24/2015 02:49 AM, Ingo Molnar wrote: > * Dave Hansen wrote: >>> Another question, related to enumeration as well: I'm wondering whether >>> there's any way for the kernel to allocate a bit or two for its own purposes - >>> such as protecting crypto keys? Or is the facility fundamentally intended for >>> user-space use only? >> >> No, that's not possible with the current setup. > > Ok, then another question, have you considered the following usecase: > > AFAICS pkeys only affect data loads and stores. Instruction fetches are notably > absent from the documentation. Can you clarify that instructions can be fetched > and executed from PTE_READ but pkeys-all-access-disabled pags? That is my understanding. I don't have a test for it, but I'll go make one. > If yes then this could be a significant security feature / usecase for pkeys: > executable sections of shared libraries and binaries could be mapped with pkey > access disabled. If I read the Intel documentation correctly then that should be > possible. Agreed. I've even heard from some researchers who are interested in this: https://www.infsec.cs.uni-saarland.de/wp-content/uploads/sites/2/2014/10/nuernberger2014ccs_disclosure.pdf > I.e. AFAICS pkeys could be used to create true '--x' permissions for executable > (user-space) pages. Just remember that all of the protections are dependent on the contents of PKRU. If an attacker controls the Access-Disable bit in PKRU for the executable-only region, you're sunk. But, that either requires being able to construct and execute arbitrary code *or* call existing code that sets PKRU to the desired values. Which, I guess, gets harder to do if all of the the wrpkru's are *in* the execute-only area. -- 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