linux-kernel - [PATCH v3 3/3] vhost: Don't call log_access

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Date:   Sat, 03 Oct 2020 12:02:13 +0200
From:   Greg Kurz <groug@...d.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, Laurent Vivier <laurent@...ier.eu>,
        David Gibson <david@...son.dropbear.id.au>
Subject: [PATCH v3 3/3] vhost: Don't call log_access_ok() when using IOTLB

When the IOTLB device is enabled, the log_guest_addr that is passed by
userspace to the VHOST_SET_VRING_ADDR ioctl, and which is then written
to vq->log_addr, is a GIOVA. All writes to this address are translated
by log_user() to writes to an HVA, and then ultimately logged through
the corresponding GPAs in log_write_hva(). No logging will ever occur
with vq->log_addr in this case. It is thus wrong to pass vq->log_addr
and log_guest_addr to log_access_vq() which assumes they are actual
GPAs.

Introduce a new vq_log_used_access_ok() helper that only checks accesses
to the log for the used structure when there isn't an IOTLB device around.

Signed-off-by: Greg Kurz <groug@...d.org>
---
 drivers/vhost/vhost.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 9d2c225fb518..9ad45e1d27f0 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1370,6 +1370,20 @@ bool vhost_log_access_ok(struct vhost_dev *dev)
 }
 EXPORT_SYMBOL_GPL(vhost_log_access_ok);
 
+static bool vq_log_used_access_ok(struct vhost_virtqueue *vq,
+				  void __user *log_base,
+				  bool log_used,
+				  u64 log_addr)
+{
+	/* If an IOTLB device is present, log_addr is a GIOVA that
+	 * will never be logged by log_used(). */
+	if (vq->iotlb)
+		return true;
+
+	return !log_used || log_access_ok(log_base, log_addr,
+					  vhost_get_used_size(vq, vq->num));
+}
+
 /* Verify access for write logging. */
 /* Caller should have vq mutex and device mutex */
 static bool vq_log_access_ok(struct vhost_virtqueue *vq,
@@ -1377,8 +1391,7 @@ static bool vq_log_access_ok(struct vhost_virtqueue *vq,
 {
 	return vq_memory_access_ok(log_base, vq->umem,
 				   vhost_has_feature(vq, VHOST_F_LOG_ALL)) &&
-		(!vq->log_used || log_access_ok(log_base, vq->log_addr,
-				  vhost_get_used_size(vq, vq->num)));
+		vq_log_used_access_ok(vq, log_base, vq->log_used, vq->log_addr);
 }
 
 /* Can we start vq? */
@@ -1517,9 +1530,9 @@ static long vhost_vring_set_addr(struct vhost_dev *d,
 			return -EINVAL;
 
 		/* Also validate log access for used ring if enabled. */
-		if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
-			!log_access_ok(vq->log_base, a.log_guest_addr,
-				       vhost_get_used_size(vq, vq->num)))
+		if (!vq_log_used_access_ok(vq, vq->log_base,
+				a.flags & (0x1 << VHOST_VRING_F_LOG),
+				a.log_guest_addr))
 			return -EINVAL;
 	}