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=-12.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 2691AC64E7A for ; Wed, 2 Dec 2020 01:27:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B00DA2222A for ; Wed, 2 Dec 2020 01:27:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727842AbgLBB1r (ORCPT ); Tue, 1 Dec 2020 20:27:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726063AbgLBB1p (ORCPT ); Tue, 1 Dec 2020 20:27:45 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3EF6EC0613CF; Tue, 1 Dec 2020 17:27:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DB/BEKSJxSLX85fmg+up0uwcX3Hty6pQKKY6dAFOg60=; b=MQcDuZ9RWfZ3RpK/bYNIT6Xj/l Wpwf1ORBQ51ijZ8MR78KGBAnMAyv2LtM3FLn350WIGOjxYmMcnze8T5pQNNODDCdutQzD/AsrOWjj JxC8ah4PO9b+qbz8fJM79ntcdLvMw3nlQbnTH8R7LAY4FhBGeJmFDwadSaO3A+iqWZyhJDCdWHUFP HVMMpGlsGmhHm3nb4AYfkZvFwPQ6jD38Vrq/H58GCHsd1woPq/pZtbp6hNYDv+VW6UPfzbMSYCoKp hGfTTKEjpQ6zDlco72i4MToNeP/RdY4bNzWcGgc1MuWBPxZ0SY4IP/6JTXnr7RRudHLwctR25PbHa mbqezCjA==; Received: from [54.239.6.185] (helo=freeip.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkGv5-0001ja-9s; Wed, 02 Dec 2020 01:26:59 +0000 Message-ID: <3ac692ed7dd77aa2ed23646bb1741a7b40bddcff.camel@infradead.org> Subject: Re: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page From: David Woodhouse To: Ankur Arora , Joao Martins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Paolo Bonzini , Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org Date: Wed, 02 Dec 2020 01:26:56 +0000 In-Reply-To: <2d4df59d-f945-32dc-6999-a6f711e972ea@oracle.com> References: <20190220201609.28290-1-joao.m.martins@oracle.com> <20190220201609.28290-4-joao.m.martins@oracle.com> <2d4df59d-f945-32dc-6999-a6f711e972ea@oracle.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-di6/SH4IhdnFuDYycz1/" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by merlin.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-di6/SH4IhdnFuDYycz1/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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 =3D gfn_to_page(kvm, gfn); > > > + if (is_error_page(page)) > > > + return -EINVAL; > > > + > > > + kvm->arch.xen.shinfo_addr =3D gfn; > > > + > > > + shared_info =3D page_to_virt(page); > > > + memset(shared_info, 0, sizeof(struct shared_info)); > > > + kvm->arch.xen.shinfo =3D shared_info; > > > + return 0; > > > +} > > > + > >=20 > > Hm. > >=20 > > 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? >=20 > 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_pa= ge() > 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. >=20 > 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. > >=20 > > If that was allowed, wouldn't it have been a much simpler fix for > > CVE-2019-3016? What am I missing? >=20 > Agreed. >=20 > Perhaps, Paolo can chime in with why KVM never uses pinned page > and always prefers to do cached mappings instead? >=20 > >=20 > > Should I rework these to use kvm_write_guest_cached()? >=20 > kvm_vcpu_map() would be better. The event channel logic does RMW operatio= ns > 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. What I have so far is at https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/xenpv I'll do the event channel support tomorrow and hook it up to my actual VMM to give it some more serious testing. --=-di6/SH4IhdnFuDYycz1/ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 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