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=-13.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 9EDC5C64E90 for ; Wed, 2 Dec 2020 05:21:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A87D22203 for ; Wed, 2 Dec 2020 05:21:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728502AbgLBFUr (ORCPT ); Wed, 2 Dec 2020 00:20:47 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:45616 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726228AbgLBFUq (ORCPT ); Wed, 2 Dec 2020 00:20:46 -0500 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0B253ilM174598; Wed, 2 Dec 2020 05:19:54 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=cMYiHoDqWu1caH/axLlQ3XDo3E331ceUnyp/wEwpk/k=; b=X9nHrXrYHhHHLTyrNQ1Wey+8HxaacctT8UYzqypg6QB+IInFPSutvkDx4N3qJfeD2t2j Umi/02K1vFG411Tfp+Zu2E/mYWk6tsDApUq9WcieUE6KlnmqZtDS+6V0D+SiKUJdfa0R SDdvlQaDPuMOd4BhN3S1zkL/7yHr9rKLG9zICxEus9ugASrU9xxTcvR4S7egiMtS69OP T80OzyoEIru1at9ZnAesUgqmP7LsN+vMfQlbRj95Q1SqC+CEqQMWbxqXYhos2U081c16 6hMO+zW5m9sHR5W7+U2l5ae0MMUZOPZjj9vEx4G2d2acdoIYVvPwfL7GC8E9asnTdADl IA== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 353dyqp8an-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 02 Dec 2020 05:19:54 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0B251LhA076776; Wed, 2 Dec 2020 05:17:54 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 3540fy287n-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 02 Dec 2020 05:17:54 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0B25Ho2l006448; Wed, 2 Dec 2020 05:17:50 GMT Received: from [192.168.0.108] (/70.36.60.91) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 01 Dec 2020 21:17:49 -0800 Subject: Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page To: David Woodhouse , Joao Martins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@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> <3ac692ed7dd77aa2ed23646bb1741a7b40bddcff.camel@infradead.org> From: Ankur Arora Message-ID: Date: Tue, 1 Dec 2020 21:17:47 -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: <3ac692ed7dd77aa2ed23646bb1741a7b40bddcff.camel@infradead.org> 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=9822 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 suspectscore=0 phishscore=0 mlxlogscore=999 adultscore=0 mlxscore=0 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012020031 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9822 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 bulkscore=0 clxscore=1015 mlxscore=0 spamscore=0 priorityscore=1501 mlxlogscore=999 suspectscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012020031 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-12-01 5:26 p.m., David Woodhouse wrote > On Tue, 2020-12-01 at 16:40 -0800, 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(). > > OK, thanks. > >> 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. > > It needs to allow updates as well as disabling the shared_info pages. > We're going to need that to implement SHUTDOWN_soft_reset for kexec. True. > >>> >>> 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? >> >>> >>> 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. > > I've ported the shared_info/vcpu_info parts and made a test case, and > was going back through to make it use kvm_write_guest_cached(). But I > should probably plug on through the evtchn bits before I do that. > > I also don't see much locking on the cache, and can't convince myself > that accessing the shared_info page from multiple CPUs with > kvm_write_guest_cached() or kvm_map_gfn() is sane unless they each have > their own cache. I think you could get a VCPU specific cache with kvm_vcpu_map(). > > What I have so far is at > > https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/xenpv Thanks. Will take a look there. Ankur > > I'll do the event channel support tomorrow and hook it up to my actual > VMM to give it some more serious testing. >