From 486647551223cc01f4dba87197030bbf4e674f0f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
Date: Thu, 21 Jul 2022 15:24:48 +0200
Subject: [PATCH 01/32] vhost: Track descriptor chain in private at SVQ
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RH-Author: Eugenio Pérez <eperezma@redhat.com>
RH-MergeRequest: 108: Net Control Virtqueue shadow Support
RH-Commit: [1/27] 26d16dc383e3064ac6e4288d5c52b39fee0ad204 (eperezmartin/qemu-kvm)
RH-Bugzilla: 1939363
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>

Bugzilla: https://bugzilla.redhat.com/1939363

Upstream Status: git://git.qemu.org/qemu.git

commit 495fe3a78749c39c0e772c4e1a55d6cb8a7e5292
Author: Eugenio Pérez <eperezma@redhat.com>
Date:   Thu May 12 19:57:42 2022 +0200

    vhost: Track descriptor chain in private at SVQ

    The device could have access to modify them, and it definitely have
    access when we implement packed vq. Harden SVQ maintaining a private
    copy of the descriptor chain. Other fields like buffer addresses are
    already maintained sepparatedly.

    Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
    Message-Id: <20220512175747.142058-2-eperezma@redhat.com>
    Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 12 +++++++-----
 hw/virtio/vhost-shadow-virtqueue.h |  6 ++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index b232803d1b..3155801f50 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -138,6 +138,7 @@ static void vhost_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr *sg,
     for (n = 0; n < num; n++) {
         if (more_descs || (n + 1 < num)) {
             descs[i].flags = flags | cpu_to_le16(VRING_DESC_F_NEXT);
+            descs[i].next = cpu_to_le16(svq->desc_next[i]);
         } else {
             descs[i].flags = flags;
         }
@@ -145,10 +146,10 @@ static void vhost_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr *sg,
         descs[i].len = cpu_to_le32(iovec[n].iov_len);
 
         last = i;
-        i = cpu_to_le16(descs[i].next);
+        i = cpu_to_le16(svq->desc_next[i]);
     }
 
-    svq->free_head = le16_to_cpu(descs[last].next);
+    svq->free_head = le16_to_cpu(svq->desc_next[last]);
 }
 
 static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
@@ -336,7 +337,6 @@ static void vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
 static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
                                            uint32_t *len)
 {
-    vring_desc_t *descs = svq->vring.desc;
     const vring_used_t *used = svq->vring.used;
     vring_used_elem_t used_elem;
     uint16_t last_used;
@@ -365,7 +365,7 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
         return NULL;
     }
 
-    descs[used_elem.id].next = svq->free_head;
+    svq->desc_next[used_elem.id] = svq->free_head;
     svq->free_head = used_elem.id;
 
     *len = used_elem.len;
@@ -540,8 +540,9 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
     svq->vring.used = qemu_memalign(qemu_real_host_page_size, device_size);
     memset(svq->vring.used, 0, device_size);
     svq->ring_id_maps = g_new0(VirtQueueElement *, svq->vring.num);
+    svq->desc_next = g_new0(uint16_t, svq->vring.num);
     for (unsigned i = 0; i < svq->vring.num - 1; i++) {
-        svq->vring.desc[i].next = cpu_to_le16(i + 1);
+        svq->desc_next[i] = cpu_to_le16(i + 1);
     }
 }
 
@@ -574,6 +575,7 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
         virtqueue_detach_element(svq->vq, next_avail_elem, 0);
     }
     svq->vq = NULL;
+    g_free(svq->desc_next);
     g_free(svq->ring_id_maps);
     qemu_vfree(svq->vring.desc);
     qemu_vfree(svq->vring.used);
diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index e5e24c536d..c132c994e9 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -53,6 +53,12 @@ typedef struct VhostShadowVirtqueue {
     /* Next VirtQueue element that guest made available */
     VirtQueueElement *next_guest_avail_elem;
 
+    /*
+     * Backup next field for each descriptor so we can recover securely, not
+     * needing to trust the device access.
+     */
+    uint16_t *desc_next;
+
     /* Next head to expose to the device */
     uint16_t shadow_avail_idx;
 
-- 
2.31.1