Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753696AbcCGTtg (ORCPT ); Mon, 7 Mar 2016 14:49:36 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:26399 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753546AbcCGTpk (ORCPT ); Mon, 7 Mar 2016 14:45:40 -0500 Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity (ADI) To: Andy Lutomirski References: <1456951177-23579-1-git-send-email-khalid.aziz@oracle.com> <20160305.230702.1325379875282120281.davem@davemloft.net> <56DD9949.1000106@oracle.com> <20160307.115626.807716799249471744.davem@davemloft.net> <56DDC2B6.6020009@oracle.com> <56DDC6E0.4000907@oracle.com> Cc: David Miller , Jonathan Corbet , Andrew Morton , dingel@linux.vnet.ibm.com, bob.picco@oracle.com, "Kirill A. Shutemov" , "Aneesh Kumar K.V" , Andrea Arcangeli , Arnd Bergmann , sparclinux@vger.kernel.org, Rob Gardner , Michal Hocko , chris.hyser@oracle.com, Richard Weinberger , Vlastimil Babka , Konstantin Khlebnikov , Oleg Nesterov , Greg Thelen , Jan Kara , xiexiuqi@huawei.com, Vineet.Gupta1@synopsys.com, Andrew Lutomirski , "Eric W. Biederman" , Benjamin Segall , Geert Uytterhoeven , Davidlohr Bueso , Alexey Dobriyan , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , linux-arch , Linux API From: Khalid Aziz Organization: Oracle Corp Message-ID: <56DDDA31.9090105@oracle.com> Date: Mon, 7 Mar 2016 12:44:49 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2279 Lines: 64 On 03/07/2016 11:49 AM, Andy Lutomirski wrote: > On Mon, Mar 7, 2016 at 10:22 AM, Khalid Aziz wrote: >> No, it changes the tag associated with the virtual address for the caller. >> Physical page backing this virtual address is unaffected. Tag checking is >> done for virtual addresses. The one restriction where physical address is >> relevant is when two processes map the same physical page, they both have to >> use the same tag for the virtual addresses that map on to the shared >> physical pages. > > Slow down, please. *Why* do the tags for two different VAs that map > to the same PA have to match? What goes wrong if they don't, and why > is requiring them to be the same a good idea? > Consider this scenario: 1. Process A creates a shm and attaches to it. 2. Process A fills shm with data it wants to share with only known processes. It enables ADI and sets tags on the shm. 3. Hacker triggers something like stack overflow on process A, exec's a new rogue binary and manages to attach to this shm. MMU knows tags were set on the virtual address mapping to the physical pages hosting the shm. If MMU does not require the rogue process to set the exact same tags on its mapping of the same shm, rogue process has defeated the ADI protection easily. Does this make sense? >> >>> >>> I sense DoS issues in your future. >>> >> >> Are you concerned about DoS even if the tag is associated with virtual >> address, not physical address? > > Yes, absolutely. > > fd = open("/lib/ld.so"); > mmap(fd) > stxa to write the tag > > *boom*, presumably, because the tags apparently have to match for all mappings. > A process can not just write version tags and make the file inaccessible to others. It takes three steps to enable ADI: 1. Set PSTATE.mcde for the process. 2. Set TTE.mcd on all PTEs for the virtual addresses ADI is being enabled on. 3. Set version tags. Unless all three steps are taken, tag checking will not be done. stxa will fail unless step 2 is completed. In your example, the step of setting TTE.mcd will force sharing to stop for the process through change_protection(), right? Thanks for asking these tough questions. These are very helpful in refining my implementation and avoiding silly bugs. -- Khalid