Re: [PATCH 1/7] s390: zcrypt: driver callback to indicate resource in use

[Pierre Morel <pmorel@linux.ibm.com>]

On 11/04/2019 23:03, Tony Krowiak wrote:
> Introduces a new driver callback to prevent a root user from unbinding
> an AP queue from its device driver if the queue is in use. This prevents
> a root user from inadvertently taking a queue away from a guest and
> giving it to the host, or vice versa. The callback will be invoked
> whenever a change to the AP bus's apmask or aqmask sysfs interfaces may
> result in one or more AP queues being removed from its driver. If the
> callback responds in the affirmative for any driver queried, the change
> to the apmask or aqmask will be rejected with a device in use error.
> 
> For this patch, only non-default drivers will be queried. Currently,
> there is only one non-default driver, the vfio_ap device driver. The
> vfio_ap device driver manages AP queues passed through to one or more
> guests and we don't want to unexpectedly take AP resources away from
> guests which are most likely independently administered.
> 
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
>   drivers/s390/crypto/ap_bus.c | 138 +++++++++++++++++++++++++++++++++++++++++--
>   drivers/s390/crypto/ap_bus.h |   3 +
>   2 files changed, 135 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
> index 1546389d71db..66a5a9d9fae6 100644
> --- a/drivers/s390/crypto/ap_bus.c
> +++ b/drivers/s390/crypto/ap_bus.c
> @@ -35,6 +35,7 @@
>   #include <linux/mod_devicetable.h>
>   #include <linux/debugfs.h>
>   #include <linux/ctype.h>
> +#include <linux/module.h>
>   
>   #include "ap_bus.h"
>   #include "ap_debug.h"
> @@ -980,9 +981,11 @@ int ap_parse_mask_str(const char *str,
>   	newmap = kmalloc(size, GFP_KERNEL);
>   	if (!newmap)
>   		return -ENOMEM;
> -	if (mutex_lock_interruptible(lock)) {
> -		kfree(newmap);
> -		return -ERESTARTSYS;
> +	if (lock) {
> +		if (mutex_lock_interruptible(lock)) {
> +			kfree(newmap);
> +			return -ERESTARTSYS;
> +		}
>   	}
>   
>   	if (*str == '+' || *str == '-') {
> @@ -994,7 +997,10 @@ int ap_parse_mask_str(const char *str,
>   	}
>   	if (rc == 0)
>   		memcpy(bitmap, newmap, size);
> -	mutex_unlock(lock);
> +
> +	if (lock)
> +		mutex_unlock(lock);
> +
>   	kfree(newmap);
>   	return rc;
>   }
> @@ -1181,12 +1187,72 @@ static ssize_t apmask_show(struct bus_type *bus, char *buf)
>   	return rc;
>   }
>   
> +static int __verify_card_reservations(struct device_driver *drv, void *data)
> +{
> +	int rc = 0;
> +	struct ap_driver *ap_drv = to_ap_drv(drv);
> +	unsigned long *newapm = (unsigned long *)data;
> +
> +	/*
> +	 * If the reserved bits do not identify cards reserved for use by the
> +	 * non-default driver, there is no need to verify the driver is using
> +	 * the queues.
> +	 */
> +	if (ap_drv->flags & AP_DRIVER_FLAG_DEFAULT)
> +		return 0;

I prefer you suppress this asymmetry with the assumption that the 
"default driver" will not register a "in_use" callback.


> +
> +	/* Pin the driver's module code */
> +	if (!try_module_get(drv->owner))
> +		return 0;
> +
> +	if (ap_drv->in_use)
> +		if (ap_drv->in_use(newapm, ap_perms.aqm))
> +			rc = -EADDRINUSE;
> +
> +	module_put(drv->owner);
> +
> +	return rc;
> +}
> +

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany