From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8AA2FC6369E for ; Wed, 2 Dec 2020 20:37:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1FF6F21527 for ; Wed, 2 Dec 2020 20:37:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727622AbgLBUgu (ORCPT ); Wed, 2 Dec 2020 15:36:50 -0500 Received: from aserp2120.oracle.com ([141.146.126.78]:35474 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726932AbgLBUgt (ORCPT ); Wed, 2 Dec 2020 15:36:49 -0500 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0B2KZA1o004516; Wed, 2 Dec 2020 20:35:47 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-2020-01-29; bh=NoO5ZnzUZTiGXgB6FbPwx93nxD9U/2l3gbD+Xy+Gcqs=; b=HWMEOjQDpoIfWipEOdbYLD+WpaUc7r5sg09FV3aRcf2bN8FAzgQAJ4KvhnMFKkCxLZNC O5rvkyAJxVLeo3xX+IVbDJCFU8mZ/i4oZCusbUA1P+vdizThroWj2vPUxp7YaGPHK8X2 iC9CluRvHPDEdKoYbOJtmyOhuSZeNdtgsaCH5obYsyXxRFsCWTS61w+XCAIboedAIIuy OS2bwsNlE/OSqubgY73nuQmKYQ9myaPYm/DBMTU/zctTMXNTuUXdHX7acfYSX9LblY8r dsO5wwjFd4OvDiatnHJQVmcy4A6QUTjB+aoeVLh1tdUHxMcTIj6nO7tOsEhp48PAQoqv OA== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by aserp2120.oracle.com with ESMTP id 353egktjuy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 02 Dec 2020 20:35:47 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0B2KUMAn125704; Wed, 2 Dec 2020 20:33:46 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3020.oracle.com with ESMTP id 3540auuvsm-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 02 Dec 2020 20:33:46 +0000 Received: from abhmp0019.oracle.com (abhmp0019.oracle.com [141.146.116.25]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 0B2KXjkF015423; Wed, 2 Dec 2020 20:33:45 GMT Received: from [10.159.240.123] (/10.159.240.123) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 02 Dec 2020 12:33:45 -0800 Subject: Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page To: Joao Martins , David Woodhouse Cc: Boris Ostrovsky , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20190220201609.28290-1-joao.m.martins@oracle.com> <20190220201609.28290-4-joao.m.martins@oracle.com> <2d4df59d-f945-32dc-6999-a6f711e972ea@oracle.com> <896dc984-fa71-8f2f-d12b-458294f5f706@oracle.com> From: Ankur Arora Message-ID: Date: Wed, 2 Dec 2020 12:33:43 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <896dc984-fa71-8f2f-d12b-458294f5f706@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9823 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 bulkscore=0 phishscore=0 mlxscore=0 adultscore=0 malwarescore=0 suspectscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012020122 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9823 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 bulkscore=0 suspectscore=0 phishscore=0 mlxlogscore=999 lowpriorityscore=0 malwarescore=0 priorityscore=1501 spamscore=0 impostorscore=0 clxscore=1015 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012020123 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-12-02 2:44 a.m., Joao Martins wrote: > [late response - was on holiday yesterday] > > On 12/2/20 12:40 AM, Ankur Arora wrote: >> On 2020-12-01 5:07 a.m., David Woodhouse wrote: >>> On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote: >>>> +static int kvm_xen_shared_info_init(struct kvm *kvm, gfn_t gfn) >>>> +{ >>>> + struct shared_info *shared_info; >>>> + struct page *page; >>>> + >>>> + page = gfn_to_page(kvm, gfn); >>>> + if (is_error_page(page)) >>>> + return -EINVAL; >>>> + >>>> + kvm->arch.xen.shinfo_addr = gfn; >>>> + >>>> + shared_info = page_to_virt(page); >>>> + memset(shared_info, 0, sizeof(struct shared_info)); >>>> + kvm->arch.xen.shinfo = shared_info; >>>> + return 0; >>>> +} >>>> + >>> >>> Hm. >>> >>> How come we get to pin the page and directly dereference it every time, >>> while kvm_setup_pvclock_page() has to use kvm_write_guest_cached() >>> instead? >> >> So looking at my WIP trees from the time, this is something that >> we went back and forth on as well with using just a pinned page or a >> persistent kvm_vcpu_map(). >> >> I remember distinguishing shared_info/vcpu_info from kvm_setup_pvclock_page() >> as shared_info is created early and is not expected to change during the >> lifetime of the guest which didn't seem true for MSR_KVM_SYSTEM_TIME (or >> MSR_KVM_STEAL_TIME) so that would either need to do a kvm_vcpu_map() >> kvm_vcpu_unmap() dance or do some kind of synchronization. >> >> That said, I don't think this code explicitly disallows any updates >> to shared_info. >> >>> >>> If that was allowed, wouldn't it have been a much simpler fix for >>> CVE-2019-3016? What am I missing? >> >> Agreed. >> >> Perhaps, Paolo can chime in with why KVM never uses pinned page >> and always prefers to do cached mappings instead? >> > Part of the CVE fix to not use cached versions. > > It's not a longterm pin of the page unlike we try to do here (partly due to the nature > of the pages we are mapping) but we still we map the gpa, RMW the steal time struct, and > then unmap the page. > > See record_steal_time() -- but more specifically commit b043138246 ("x86/KVM: Make sure > KVM_VCPU_FLUSH_TLB flag is not missed"). > > But I am not sure it's a good idea to follow the same as record_steal_time() given that > this is a fairly sensitive code path for event channels. > >>> >>> Should I rework these to use kvm_write_guest_cached()? >> >> kvm_vcpu_map() would be better. The event channel logic does RMW operations >> on shared_info->vcpu_info. >> > Indeed, yes. > > Ankur IIRC, we saw missed event channels notifications when we were using the > {write,read}_cached() version of the patch. > > But I can't remember the reason it was due to, either the evtchn_pending or the mask > word -- which would make it not inject an upcall. If memory serves, it was the mask. Though I don't think that we had kvm_{write,read}_cached in use at that point -- given that they were definitely not RMW safe. Ankur > > Joao >