linux-kernel - [PATCH 3.13.y-ckt 109/132] KVM: s390: virtio-ccw: don't overwrite config space values

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Message-Id: <1437616850-23266-110-git-send-email-kamal@canonical.com>
Date:	Wed, 22 Jul 2015 19:00:27 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13.y-ckt 109/132] KVM: s390: virtio-ccw: don't overwrite config space values

3.13.11-ckt24 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cornelia Huck <cornelia.huck@...ibm.com>

commit 431dae778aea4eed31bd12e5ee82edc571cd4d70 upstream.

Eric noticed problems with vhost-scsi and virtio-ccw: vhost-scsi
complained about overwriting values in the config space, which
was triggered by a broken implementation of virtio-ccw's config
get/set routines. It was probably sheer luck that we did not hit
this before.

When writing a value to the config space, the WRITE_CONF ccw will
always write from the beginning of the config space up to and
including the value to be set. If the config space up to the value
has not yet been retrieved from the device, however, we'll end up
overwriting values. Keep track of the known config space and update
if needed to avoid this.

Moreover, READ_CONF will only read the number of bytes it has been
instructed to retrieve, so we must not copy more than that to the
buffer, or we might overwrite trailing values.

Reported-by: Eric Farman <farman@...ux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>
Reviewed-by: Eric Farman <farman@...ux.vnet.ibm.com>
Tested-by: Eric Farman <farman@...ux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/s390/kvm/virtio_ccw.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
index d629717..9effcf5 100644
--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -58,6 +58,7 @@ struct virtio_ccw_device {
 	unsigned long indicators;
 	unsigned long indicators2;
 	struct vq_config_block *config_block;
+	unsigned int config_ready;
 };
 
 struct vq_info_block {
@@ -504,8 +505,11 @@ static void virtio_ccw_get_config(struct virtio_device *vdev,
 	if (ret)
 		goto out_free;
 
-	memcpy(vcdev->config, config_area, sizeof(vcdev->config));
-	memcpy(buf, &vcdev->config[offset], len);
+	memcpy(vcdev->config, config_area, offset + len);
+	if (buf)
+		memcpy(buf, &vcdev->config[offset], len);
+	if (vcdev->config_ready < offset + len)
+		vcdev->config_ready = offset + len;
 
 out_free:
 	kfree(config_area);
@@ -528,6 +532,9 @@ static void virtio_ccw_set_config(struct virtio_device *vdev,
 	if (!config_area)
 		goto out_free;
 
+	/* Make sure we don't overwrite fields. */
+	if (vcdev->config_ready < offset)
+		virtio_ccw_get_config(vdev, 0, NULL, offset);
 	memcpy(&vcdev->config[offset], buf, len);
 	/* Write the config area to the host. */
 	memcpy(config_area, vcdev->config, sizeof(vcdev->config));
-- 
1.9.1

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