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Subject[PATCH 3.16 271/305] virtio/s390: avoid race on vcdev->config
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Halil Pasic <pasic@linux.ibm.com>

commit 2448a299ec416a80f699940a86f4a6d9a4f643b1 upstream.

Currently we have a race on vcdev->config in virtio_ccw_get_config() and
in virtio_ccw_set_config().

This normally does not cause problems, as these are usually infrequent
operations. However, for some devices writing to/reading from the config
space can be triggered through sysfs attributes. For these, userspace can
force the race by increasing the frequency.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <20180925121309.58524-2-pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/s390/kvm/virtio_ccw.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -741,6 +741,7 @@ static void virtio_ccw_get_config(struct
int ret;
struct ccw1 *ccw;
void *config_area;
+ unsigned long flags;

ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
if (!ccw)
@@ -759,11 +760,13 @@ static void virtio_ccw_get_config(struct
if (ret)
goto out_free;

+ spin_lock_irqsave(&vcdev->lock, flags);
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;
+ spin_unlock_irqrestore(&vcdev->lock, flags);
+ if (buf)
+ memcpy(buf, config_area + offset, len);

out_free:
kfree(config_area);
@@ -777,6 +780,7 @@ static void virtio_ccw_set_config(struct
struct virtio_ccw_device *vcdev = to_vc_device(vdev);
struct ccw1 *ccw;
void *config_area;
+ unsigned long flags;

ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
if (!ccw)
@@ -789,9 +793,11 @@ static void virtio_ccw_set_config(struct
/* Make sure we don't overwrite fields. */
if (vcdev->config_ready < offset)
virtio_ccw_get_config(vdev, 0, NULL, offset);
+ spin_lock_irqsave(&vcdev->lock, flags);
memcpy(&vcdev->config[offset], buf, len);
/* Write the config area to the host. */
memcpy(config_area, vcdev->config, sizeof(vcdev->config));
+ spin_unlock_irqrestore(&vcdev->lock, flags);
ccw->cmd_code = CCW_CMD_WRITE_CONF;
ccw->flags = 0;
ccw->count = offset + len;
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