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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 E0664C4708F for ; Thu, 3 Jun 2021 00:41:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C0759613EA for ; Thu, 3 Jun 2021 00:41:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229814AbhFCAnb (ORCPT ); Wed, 2 Jun 2021 20:43:31 -0400 Received: from mga11.intel.com ([192.55.52.93]:55025 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229567AbhFCAna (ORCPT ); Wed, 2 Jun 2021 20:43:30 -0400 IronPort-SDR: p4FHmcKknfBhxyjNIDNM8DVNAP72bZcZitBv6dpBSjvEe/6vZwrXG1xK0gkvrSRTgTrj6tADqe XS16pKMQkttQ== X-IronPort-AV: E=McAfee;i="6200,9189,10003"; a="200919097" X-IronPort-AV: E=Sophos;i="5.83,244,1616482800"; d="scan'208";a="200919097" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2021 17:41:46 -0700 IronPort-SDR: RcO/ziDZiA0zs9KDBzMVcDfkcrCyK0CG+VkWlPWMtZabfLPdUI3KlbztMzBnu5W2HGau7uO170 UmLD4vf1CVKw== X-IronPort-AV: E=Sophos;i="5.83,244,1616482800"; d="scan'208";a="549686675" Received: from tassilo.jf.intel.com ([10.54.74.11]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2021 17:41:44 -0700 From: Andi Kleen To: mst@redhat.com Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org, hch@lst.de, m.szyprowski@samsung.com, robin.murphy@arm.com, iommu@lists.linux-foundation.org, x86@kernel.org, sathyanarayanan.kuppuswamy@linux.intel.com, jpoimboe@redhat.com, linux-kernel@vger.kernel.org, Andi Kleen Subject: [PATCH v1 1/8] virtio: Force only split mode with protected guest Date: Wed, 2 Jun 2021 17:41:26 -0700 Message-Id: <20210603004133.4079390-2-ak@linux.intel.com> X-Mailer: git-send-email 2.25.4 In-Reply-To: <20210603004133.4079390-1-ak@linux.intel.com> References: <20210603004133.4079390-1-ak@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When running under TDX the virtio host is untrusted. The bulk of the kernel memory is encrypted and protected, but the virtio ring is in special shared memory that is shared with the untrusted host. This means virtio needs to be hardened against any attacks from the host through the ring. Of course it's impossible to prevent DOS (the host can chose at any time to stop doing IO), but there should be no buffer overruns or similar that might give access to any private memory in the guest. virtio has a lot of modes, most are difficult to harden. The best for hardening seems to be split mode without indirect descriptors. This also simplifies the hardening job because it's only a single code path. Only allow split mode when in a protected guest. Followon patches harden the split mode code paths, and we don't want an malicious host to force anything else. Also disallow indirect mode for similar reasons. Signed-off-by: Andi Kleen --- drivers/virtio/virtio_ring.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 71e16b53e9c1..f35629fa47b1 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #ifdef DEBUG @@ -2221,8 +2222,16 @@ void vring_transport_features(struct virtio_device *vdev) unsigned int i; for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) { + + /* + * In protected guest mode disallow packed or indirect + * because they ain't hardened. + */ + switch (i) { case VIRTIO_RING_F_INDIRECT_DESC: + if (protected_guest_has(VM_MEM_ENCRYPT)) + goto clear; break; case VIRTIO_RING_F_EVENT_IDX: break; @@ -2231,9 +2240,12 @@ void vring_transport_features(struct virtio_device *vdev) case VIRTIO_F_ACCESS_PLATFORM: break; case VIRTIO_F_RING_PACKED: + if (protected_guest_has(VM_MEM_ENCRYPT)) + goto clear; break; case VIRTIO_F_ORDER_PLATFORM: break; + clear: default: /* We don't understand this bit. */ __virtio_clear_bit(vdev, i); -- 2.25.4