From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752206AbcGSUpO (ORCPT ); Tue, 19 Jul 2016 16:45:14 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:49824 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752162AbcGSUpK (ORCPT ); Tue, 19 Jul 2016 16:45:10 -0400 X-IBM-Helo: d06dlp03.portsmouth.uk.ibm.com X-IBM-MailFrom: borntraeger@de.ibm.com X-IBM-RcptTo: linux-arch@vger.kernel.org;linux-ia64@vger.kernel.org;linux-kernel@vger.kernel.org;sparclinux@vger.kernel.org Subject: Re: [PATCH v3 02/11] mm: Hardened usercopy To: Kees Cook References: <1468619065-3222-1-git-send-email-keescook@chromium.org> <1468619065-3222-3-git-send-email-keescook@chromium.org> <578DF109.5030704@de.ibm.com> <578E8A22.5080807@de.ibm.com> Cc: LKML , Balbir Singh , Daniel Micay , Josh Poimboeuf , Rik van Riel , Casey Schaufler , PaX Team , Brad Spengler , Russell King , Catalin Marinas , Will Deacon , Ard Biesheuvel , Benjamin Herrenschmidt , Michael Ellerman , Tony Luck , Fenghua Yu , "David S. Miller" , "x86@kernel.org" , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Andy Lutomirski , Borislav Petkov , Mathias Krause , Jan Kara , Vitaly Wool , Andrea Arcangeli , Dmitry Vyukov , Laura Abbott , "linux-arm-kernel@lists.infradead.org" , linux-ia64@vger.kernel.org, "linuxppc-dev@lists.ozlabs.org" , sparclinux , linux-arch , Linux-MM , "kernel-hardening@lists.openwall.com" From: Christian Borntraeger Date: Tue, 19 Jul 2016 22:44:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16071920-0040-0000-0000-00000201879F X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16071920-0041-0000-0000-00002109EE55 Message-Id: <578E914A.7070900@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-19_14:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1607190220 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/19/2016 10:34 PM, Kees Cook wrote: [...] >> >> So what about for the CONFIG text: >> >> An architecture should select this if the kernel mapping has a secondary >> linear mapping of the kernel text - in other words more than one virtual >> kernel address that points to the kernel image. This is used to verify >> that kernel text exposures are not visible under CONFIG_HARDENED_USERCOPY. > > Sounds good, I've adjusted it for now. > >>> I wonder if I can avoid the CONFIG entirely if I just did a >>> __va(__pa(_stext)) != _stext test... would that break anyone? >> >> Can this be resolved on all platforms at compile time? > > Well, I think it still needs a runtime check (compile-time may not be > able to tell about kaslr, or who knows what else). I would really like > to avoid the CONFIG if possible, though. Would this do the right thing > on s390? This appears to work where I'm able to test it (32/64 x86, > 32/64 arm): > > unsigned long textlow = (unsigned long)_stext; > unsigned long texthigh = (unsigned long)_etext; > unsigned long textlow_linear = (unsigned long)__va(__pa(textlow); > unsigned long texthigh_linear = (unsigned long)__va(__pa(texthigh); > as we have #define PAGE_OFFSET 0x0UL #define __pa(x) (unsigned long)(x) #define __va(x) (void *)(unsigned long)(x) both should be identical on s390 as of today, so it should work fine and only do the check once > if (overlaps(ptr, n, textlow, texthigh)) > return ""; > > /* Check against possible secondary linear mapping as well. */ > if (textlow != textlow_linear && > overlaps(ptr, n, textlow_linear, texthigh_linear)) > return ""; > > return NULL; > > > -Kees > PS: Not sure how useful and flexible this offers is but you can get some temporary free access to an s390 on https://developer.ibm.com/linuxone/