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[156.151.31.86]) by mx.google.com with ESMTPS id t18si46703611plo.113.2019.04.17.09.50.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Apr 2019 09:50:35 -0700 (PDT) Received-SPF: pass (google.com: domain of khalid.aziz@oracle.com designates 156.151.31.86 as permitted sender) client-ip=156.151.31.86; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b=QSc54vhj; spf=pass (google.com: domain of khalid.aziz@oracle.com designates 156.151.31.86 as permitted sender) smtp.mailfrom=khalid.aziz@oracle.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x3HGnG3X054958; Wed, 17 Apr 2019 16:49:35 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=Pt0iK48BFNYGn2PcXPZIgKCS+ChPFURYRr28gHDNt5M=; b=QSc54vhjKse2Gq1rcTB1KDv+n5ZNYuiktD723uSnPsQg7/lU0erFzUS/U+FBFZ5v5LN9 4iDgkm0iqKmiYtxwHEIhhS/dZpybhW0dtoiBsKHfsRiNS/33zdpDmnSeEYaMYsWJC471 dCGjeqzxijoOujPRbY2v3RHQK3LQ0lDNqJDLxAdspRBmSrV8REgdAzENjYqfKctb9EN3 ONxMYYcd+On4oXsuj8M0FhxjRbw/Mu/K0czjCGbHDVfpbP3Gtg6t7AiiaqxMW+yFQXEF 2d2DLE521La9q/IPFvG820wM8B3HmquyOp/lJk9noCrcYUs7OpW7XPbO3bgHsYkbl4gL UQ== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by userp2130.oracle.com with ESMTP id 2rvwk3v9bb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 17 Apr 2019 16:49:35 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x3HGmQda049331; Wed, 17 Apr 2019 16:49:34 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3020.oracle.com with ESMTP id 2rv2tvg02m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 17 Apr 2019 16:49:34 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x3HGnUSU030371; Wed, 17 Apr 2019 16:49:30 GMT Received: from [10.65.150.207] (/10.65.150.207) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 17 Apr 2019 09:49:29 -0700 Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO) To: Ingo Molnar Cc: juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de, keescook@google.com, konrad.wilk@oracle.com, Juerg Haefliger , deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, iommu@lists.linux-foundation.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, Khalid Aziz , Linus Torvalds , Andrew Morton , Thomas Gleixner , Andy Lutomirski , Peter Zijlstra , Dave Hansen , Borislav Petkov , "H. Peter Anvin" , Arjan van de Ven , Greg Kroah-Hartman References: <20190417161042.GA43453@gmail.com> From: Khalid Aziz Organization: Oracle Corp Message-ID: Date: Wed, 17 Apr 2019 10:49:26 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190417161042.GA43453@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9230 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904170113 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9230 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904170113 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/17/19 10:15 AM, Ingo Molnar wrote: >=20 > [ Sorry, had to trim the Cc: list from hell. Tried to keep all the=20 > mailing lists and all x86 developers. ] >=20 > * Khalid Aziz wrote: >=20 >> From: Juerg Haefliger >> >> This patch adds basic support infrastructure for XPFO which protects=20 >> against 'ret2dir' kernel attacks. The basic idea is to enforce=20 >> exclusive ownership of page frames by either the kernel or userspace, = >> unless explicitly requested by the kernel. Whenever a page destined fo= r=20 >> userspace is allocated, it is unmapped from physmap (the kernel's page= =20 >> table). When such a page is reclaimed from userspace, it is mapped bac= k=20 >> to physmap. Individual architectures can enable full XPFO support usin= g=20 >> this infrastructure by supplying architecture specific pieces. >=20 > I have a higher level, meta question: >=20 > Is there any updated analysis outlining why this XPFO overhead would be= =20 > required on x86-64 kernels running on SMAP/SMEP CPUs which should be al= l=20 > recent Intel and AMD CPUs, and with kernel that mark all direct kernel = > mappings as non-executable - which should be all reasonably modern=20 > kernels later than v4.0 or so? >=20 > I.e. the original motivation of the XPFO patches was to prevent executi= on=20 > of direct kernel mappings. Is this motivation still present if those=20 > mappings are non-executable? >=20 > (Sorry if this has been asked and answered in previous discussions.) Hi Ingo, That is a good question. Because of the cost of XPFO, we have to be very sure we need this protection. The paper from Vasileios, Michalis and Angelos - , does go into how ret2dir attacks can bypass SMAP/SMEP in sections 6.1 and 6.2. Thanks, Khalid