[PATCH v4 3/6] vfio-ccw: protect the I/O region

Cornelia Huck
2019-03-01T09:38:59Z

Introduce a mutex to disallow concurrent reads or writes to the
I/O region. This makes sure that the data the kernel or user
space see is always consistent.

The same mutex will be used to protect the async region as well.

Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
drivers/s390/cio/vfio_ccw_drv.c | 3 +++
drivers/s390/cio/vfio_ccw_ops.c | 28 +++++++++++++++++++---------
drivers/s390/cio/vfio_ccw_private.h | 2 ++
3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index 0b3b9de45c60..5ea0da1dd954 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -84,7 +84,9 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
if (is_final)
cp_free(&private->cp);
}
+ mutex_lock(&private->io_mutex);
memcpy(private->io_region->irb_area, irb, sizeof(*irb));
+ mutex_unlock(&private->io_mutex);

if (private->io_trigger)
eventfd_signal(private->io_trigger, 1);
@@ -129,6 +131,7 @@ static int vfio_ccw_sch_probe(struct subchannel *sch)

private->sch = sch;
dev_set_drvdata(&sch->dev, private);
+ mutex_init(&private->io_mutex);

spin_lock_irq(sch->lock);
private->state = VFIO_CCW_STATE_NOT_OPER;
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index 3fdcc6dfe0bf..025c8a832bc8 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -169,16 +169,20 @@ static ssize_t vfio_ccw_mdev_read(struct mdev_device *mdev,
{
struct vfio_ccw_private *private;
struct ccw_io_region *region;
+ int ret;

if (*ppos + count > sizeof(*region))
return -EINVAL;

private = dev_get_drvdata(mdev_parent_dev(mdev));
+ mutex_lock(&private->io_mutex);
region = private->io_region;
if (copy_to_user(buf, (void *)region + *ppos, count))
- return -EFAULT;
-
- return count;
+ ret = -EFAULT;
+ else
+ ret = count;
+ mutex_unlock(&private->io_mutex);
+ return ret;
}

static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
@@ -188,23 +192,29 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
{
struct vfio_ccw_private *private;
struct ccw_io_region *region;
+ int ret;

if (*ppos + count > sizeof(*region))
return -EINVAL;

private = dev_get_drvdata(mdev_parent_dev(mdev));
+ if (!mutex_trylock(&private->io_mutex))
+ return -EAGAIN;

region = private->io_region;
- if (copy_from_user((void *)region + *ppos, buf, count))
- return -EFAULT;
+ if (copy_from_user((void *)region + *ppos, buf, count)) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }

vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
- if (region->ret_code != 0) {
+ if (region->ret_code != 0)
private->state = VFIO_CCW_STATE_IDLE;
- return region->ret_code;
- }
+ ret = (region->ret_code != 0) ? region->ret_code : count;

- return count;
+out_unlock:
+ mutex_unlock(&private->io_mutex);
+ return ret;
}

static int vfio_ccw_mdev_get_device_info(struct vfio_device_info *info)
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index 50c52efb4fcb..32173cbd838d 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -28,6 +28,7 @@
* @mdev: pointer to the mediated device
* @nb: notifier for vfio events
* @io_region: MMIO region to input/output I/O arguments/results
+ * @io_mutex: protect against concurrent update of I/O regions
* @cp: channel program for the current I/O operation
* @irb: irb info received from interrupt
* @scsw: scsw info
@@ -42,6 +43,7 @@ struct vfio_ccw_private {
struct mdev_device *mdev;
struct notifier_block nb;
struct ccw_io_region *io_region;
+ struct mutex io_mutex;

struct channel_program cp;
struct irb irb;
--
2.17.2