Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752531AbbKVP6h (ORCPT ); Sun, 22 Nov 2015 10:58:37 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:59045 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752229AbbKVP6g (ORCPT ); Sun, 22 Nov 2015 10:58:36 -0500 Message-ID: <1448207908.89124.54.camel@infradead.org> Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff From: David Woodhouse To: "Michael S. Tsirkin" Cc: Andy Lutomirski , Benjamin Herrenschmidt , Christian Borntraeger , Paolo Bonzini , "linux-kernel@vger.kernel.org" , Martin Schwidefsky , Sebastian Ott , linux-s390 , Cornelia Huck , Joerg Roedel , Linux Virtualization , Christoph Hellwig , KVM , Marcel Apfelbaum Date: Sun, 22 Nov 2015 15:58:28 +0000 In-Reply-To: <20151120085658-mutt-send-email-mst@redhat.com> References: <20151119153821-mutt-send-email-mst@redhat.com> <1447976286.145626.122.camel@infradead.org> <20151120085658-mutt-send-email-mst@redhat.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-baOU5WzwIFiou6EmhhFW" X-Mailer: Evolution 3.18.1 (3.18.1-1.fc23) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9374 Lines: 148 --=-baOU5WzwIFiou6EmhhFW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2015-11-20 at 10:21 +0200, Michael S. Tsirkin wrote: >=20 > David, there are two things a hypervisor needs to tell the guest. > 1. The actual device is behind an IOMMU. This is what you > =C2=A0=C2=A0 are suggesting we use DMAR for. > 2. Using IOMMU from kernel (as opposed to from userspace with VFIO) > =C2=A0=C2=A0 actually adds security. For exising virtio devices on KVM, > =C2=A0=C2=A0 the answer is no. And DMAR has no way to reflect that. Using the IOMMU from the kernel *always* adds security. It protects against device driver (and device) bugs which can be made exploitable by allowing DMA to anywhere in the system. Sure, there are classes of that which are far more interesting, for example where you give the whole device to a guest and let it load the firmware. But "we trust the hypervisor" and "we trust the hardware" are not *so* far apart conceptually. Hell, with ATS you *still* have to trust the hardware to a large extent. I really think that something like the proposed DMA_ATTR_IOMMU_BYPASS should suffice for the "who cares about security; we want performance" case. --=C2=A0 dwmw2 --=-baOU5WzwIFiou6EmhhFW Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB MB4XDTE1MDUwNTA5NDM0MVoXDTE2MDUwNTA5NTMzNlowQjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFk ZWFkLm9yZzEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMkbm9kPbx1j/X4RVyf/pPKSYwelcco69TvnQQbKM8m8xkWjXJI1 jpJ1jMaGUZGFToINMSZi7lZawUozudWbXSKy1SikENSTJHffsdRAIlsp+hR8vWvjsKUry6sEdqPG 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