Re: [PATCH v2 6/7] s390: vfio-ap: handle bind and unbind of AP queue device

[Tony Krowiak <akrowiak@linux.ibm.com>]

On 5/6/19 6:55 AM, Pierre Morel wrote:
> On 03/05/2019 23:14, Tony Krowiak wrote:
>> There is nothing preventing a root user from inadvertently unbinding an
>> AP queue device that is in use by a guest from the vfio_ap device driver
>> and binding it to a zcrypt driver. This can result in a queue being
>> accessible from both the host and a guest.
>>
>> This patch introduces safeguards that prevent sharing of an AP queue
>> between the host when a queue device is unbound from the vfio_ap device
>> driver. In addition, this patch restores guest access to AP queue devices
>> bound to the vfio_ap driver if the queue's APQN is assigned to an mdev
>> device in use by a guest.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_drv.c     |  12 +++-
>>   drivers/s390/crypto/vfio_ap_ops.c     | 100 
>> +++++++++++++++++++++++++++++++++-
>>   drivers/s390/crypto/vfio_ap_private.h |   2 +
>>   3 files changed, 111 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/vfio_ap_drv.c 
>> b/drivers/s390/crypto/vfio_ap_drv.c
>> index e9824c35c34f..c215978daf39 100644
>> --- a/drivers/s390/crypto/vfio_ap_drv.c
>> +++ b/drivers/s390/crypto/vfio_ap_drv.c
>> @@ -42,12 +42,22 @@ MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
>>   static int vfio_ap_queue_dev_probe(struct ap_device *apdev)
>>   {
>> +    struct ap_queue *queue = to_ap_queue(&apdev->device);
>> +
>> +    mutex_lock(&matrix_dev->lock);
>> +    vfio_ap_mdev_probe_queue(queue);
>> +    mutex_unlock(&matrix_dev->lock);
>> +
>>       return 0;
>>   }
>>   static void vfio_ap_queue_dev_remove(struct ap_device *apdev)
>>   {
>> -    /* Nothing to do yet */
>> +    struct ap_queue *queue = to_ap_queue(&apdev->device);
>> +
>> +    mutex_lock(&matrix_dev->lock);
>> +    vfio_ap_mdev_remove_queue(queue);
>> +    mutex_unlock(&matrix_dev->lock);
>>   }
>>   static void vfio_ap_matrix_dev_release(struct device *dev)
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
>> b/drivers/s390/crypto/vfio_ap_ops.c
>> index ede45184eb67..40324951bd37 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -226,8 +226,6 @@ static struct device 
>> *vfio_ap_get_queue_dev(unsigned long apid,
>>                     &apqn, match_apqn);
>>   }
>> -
>> -
>>   static int vfio_ap_mdev_validate_masks(unsigned long *apm, unsigned 
>> long *aqm)
>>   {
>>       int ret;
>> @@ -259,6 +257,27 @@ static bool vfio_ap_queues_on_drv(unsigned long 
>> *apm, unsigned long *aqm)
>>       return true;
>>   }
>> +static bool vfio_ap_card_on_drv(struct ap_queue *queue, unsigned long 
>> *aqm)
>> +{
>> +    unsigned long apid, apqi;
>> +    struct device *dev;
>> +
>> +    apid = AP_QID_CARD(queue->qid);
>> +
>> +    for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
>> +        if (queue->qid == AP_MKQID(apid, apqi))
>> +            continue;
>> +
>> +        dev = vfio_ap_get_queue_dev(apid, apqi);
>> +        if (!dev)
>> +            return false;
>> +
>> +        put_device(dev);
>> +    }
>> +
>> +    return true;
>> +}
>> +
>>   /**
>>    * assign_adapter_store
>>    *
>> @@ -1017,3 +1036,80 @@ void vfio_ap_mdev_unregister(void)
>>   {
>>       mdev_unregister_device(&matrix_dev->device);
>>   }
>> +
>> +static struct ap_matrix_mdev *vfio_ap_mdev_find_matrix_mdev(unsigned 
>> long apid,
>> +                                unsigned long apqi)
>> +{
>> +    struct ap_matrix_mdev *matrix_mdev;
>> +
>> +    list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) {
>> +        if (test_bit_inv(apid, matrix_mdev->matrix.apm) &&
>> +            test_bit_inv(apqi, matrix_mdev->matrix.aqm))
>> +            return matrix_mdev;
>> +    }
>> +
>> +    return NULL;
>> +}
>> +
>> +void vfio_ap_mdev_probe_queue(struct ap_queue *queue)
>> +{
>> +    struct ap_matrix_mdev *matrix_mdev;
>> +    unsigned long *shadow_apm, *shadow_aqm;
>> +    unsigned long apid = AP_QID_CARD(queue->qid);
>> +    unsigned long apqi = AP_QID_QUEUE(queue->qid);
>> +
>> +    /*
>> +     * Find the mdev device to which the APQN of the queue device being
>> +     * probed is assigned
>> +     */
>> +    matrix_mdev = vfio_ap_mdev_find_matrix_mdev(apid, apqi);
>> +
>> +    /* Check whether we found an mdev device and it is in use by a 
>> guest */
>> +    if (matrix_mdev && matrix_mdev->kvm) {
>> +        shadow_apm = matrix_mdev->shadow_crycb->apm;
>> +        shadow_aqm = matrix_mdev->shadow_crycb->aqm;
>> +        /*
>> +         * If the guest already has access to the adapter card
>> +         * referenced by APID or does not have access to the queues
>> +         * referenced by APQI, there is nothing to do here.
>> +         */
>> +        if (test_bit_inv(apid, shadow_apm) ||
>> +            !test_bit_inv(apqi, shadow_aqm))
>> +            return;
>> +
>> +        /*
>> +         * If each APQN with the APID of the queue being probed and an
>> +         * APQI in the shadow CRYCB references a queue device that is
>> +         * bound to the vfio_ap driver, then plug the adapter into the
>> +         * guest.
>> +         */
>> +        if (vfio_ap_card_on_drv(queue, shadow_aqm)) {
>> +            set_bit_inv(apid, shadow_apm);
>> +            vfio_ap_mdev_update_crycb(matrix_mdev);
>> +        }
>> +    }
>> +}
>> +
>> +void vfio_ap_mdev_remove_queue(struct ap_queue *queue)
>> +{
>> +    struct ap_matrix_mdev *matrix_mdev;
>> +    unsigned long apid = AP_QID_CARD(queue->qid);
>> +    unsigned long apqi = AP_QID_QUEUE(queue->qid);
>> +
>> +    matrix_mdev = vfio_ap_mdev_find_matrix_mdev(apid, apqi);
>> +
>> +    /*
>> +     * If the queue is assigned to the mdev device and the mdev device
>> +     * is in use by a guest, unplug the adapter referred to by the APID
>> +     * of the APQN of the queue being removed.
>> +     */
>> +    if (matrix_mdev && matrix_mdev->kvm) {
>> +        if (!test_bit_inv(apid, matrix_mdev->shadow_crycb->apm))
>> +            return;
>> +
>> +        clear_bit_inv(apid, matrix_mdev->shadow_crycb->apm);
>> +        vfio_ap_mdev_update_crycb(matrix_mdev);
>> +    }
>> +
>> +    vfio_ap_mdev_reset_queue(apid, apqi);
>> +}
>> diff --git a/drivers/s390/crypto/vfio_ap_private.h 
>> b/drivers/s390/crypto/vfio_ap_private.h
>> index e8457aa61976..6b1f7df5b979 100644
>> --- a/drivers/s390/crypto/vfio_ap_private.h
>> +++ b/drivers/s390/crypto/vfio_ap_private.h
>> @@ -87,5 +87,7 @@ struct ap_matrix_mdev {
>>   extern int vfio_ap_mdev_register(void);
>>   extern void vfio_ap_mdev_unregister(void);
>> +void vfio_ap_mdev_remove_queue(struct ap_queue *queue);
>> +void vfio_ap_mdev_probe_queue(struct ap_queue *queue);
>>   #endif /* _VFIO_AP_PRIVATE_H_ */
>>
> 
> 
> AFAIU the apmask/aqmask of the AP_BUS are replacing bind/unbind for the 
> admin. Don't they?

Yes, these interfaces are used to bind/unbind.

> Then why not suppress bind/unbind for ap_queues?

I did suppress them in a previous version, but I believe Harald
objected. I don't recall the reason. If any other maintainers
agree with this, I can reinstate that change. I personally would
prefer that. I think leaving the bind/unbind interfaces confuses
the issue.

> 
> Otherwise, it seems to me to handle correctly the disappearance of a 
> card, which is the only thing that can happen from out of the firmware 
> queue change requires configuration change and re-IPL.

You are correct.

> 
> Even still need testing, LGTM

I would welcome and appreciate additional testing, thanks in advance.

> 
>