Re: [PATCH v4 3/7] s390: zcrypt: driver callback to indicate resource in use

Tony Krowiak
2019-06-17T14:37:27Z

On 6/17/19 5:28 AM, Harald Freudenberger wrote:
> On 13.06.19 21:39, 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 b9fc502c58c2..1b06f47d0d1c 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"
>> @@ -998,9 +999,11 @@ 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 == '-') {
>> @@ -1012,7 +1015,10 @@ 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;
>> }
>> @@ -1199,12 +1205,72 @@ static ssize_t apmask_show(struct bus_type *bus, char *buf)
>> return rc;
>> }
>>
>> +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;
>> +
>> + /* The non-default driver's module must be loaded */
>> + 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;
>> +}
>> +
>> +static int apmask_commit(unsigned long *newapm)
>> +{
>> + int rc;
>> + unsigned long reserved[BITS_TO_LONGS(AP_DEVICES)];
>> +
>> + /*
>> + * Check if any bits in the apmask have been set which will
>> + * result in queues being removed from non-default drivers
>> + */
>> + if (bitmap_andnot(reserved, newapm, ap_perms.apm, AP_DEVICES)) {
>> + rc = (bus_for_each_drv(&ap_bus_type, NULL, reserved,
>> + __verify_card_reservations));
> Why surround the bus_for_each_drv() with additional parenthesis ?

You are right, it is not necessary.

>> + if (rc)
>> + return rc;
>> + }
>> +
>> + memcpy(ap_perms.apm, newapm, APMASKSIZE);
>> +
>> + return 0;
>> +}
>> +
>> static ssize_t apmask_store(struct bus_type *bus, const char *buf,
>> size_t count)
>> {
>> int rc;
>> + unsigned long newapm[BITS_TO_LONGS(AP_DEVICES)];
>> +
>> + memcpy(newapm, ap_perms.apm, APMASKSIZE);
>> +
>> + rc = ap_parse_mask_str(buf, newapm, AP_DEVICES, NULL);
>> + if (rc)
>> + return rc;
>> +
>> + if (mutex_lock_interruptible(&ap_perms_mutex))
>> + return -ERESTARTSYS;
> This lock is too late. Move it before the memcpy(newapm, ap_perms.apm, APMASKSIZE);

I agree, it shall be moved.

>> +
>> + rc = apmask_commit(newapm);
>> + mutex_unlock(&ap_perms_mutex);
>>
>> - rc = ap_parse_mask_str(buf, ap_perms.apm, AP_DEVICES, &ap_perms_mutex);
>> if (rc)
>> return rc;
>>
>> @@ -1230,12 +1296,72 @@ static ssize_t aqmask_show(struct bus_type *bus, char *buf)
>> return rc;
>> }
>>
>> +int __verify_queue_reservations(struct device_driver *drv, void *data)
>> +{
>> + int rc = 0;
>> + struct ap_driver *ap_drv = to_ap_drv(drv);
>> + unsigned long *newaqm = (unsigned long *)data;
>> +
>> + /*
>> + * If the reserved bits do not identify queues 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;
>> +
>> + /* The non-default driver's module must be loaded */
>> + if (!try_module_get(drv->owner))
>> + return 0;
>> +
>> + if (ap_drv->in_use)
>> + if (ap_drv->in_use(ap_perms.apm, newaqm))
>> + rc = -EADDRINUSE;
>> +
>> + module_put(drv->owner);
>> +
>> + return rc;
>> +}
>> +
>> +static int aqmask_commit(unsigned long *newaqm)
>> +{
>> + int rc;
>> + unsigned long reserved[BITS_TO_LONGS(AP_DOMAINS)];
>> +
>> + /*
>> + * Check if any bits in the aqmask have been set which will
>> + * result in queues being removed from non-default drivers
>> + */
>> + if (bitmap_andnot(reserved, newaqm, ap_perms.aqm, AP_DOMAINS)) {
>> + rc = (bus_for_each_drv(&ap_bus_type, NULL, reserved,
>> + __verify_queue_reservations));
> Same here: please remove the surrounding ( ... ).

Will do.

>> + if (rc)
>> + return rc;
>> + }
>> +
>> + memcpy(ap_perms.aqm, newaqm, APMASKSIZE);
> APMASKSIZE -> AQMASKSIZE
>> +
>> + return 0;
>> +}
>> +
>> static ssize_t aqmask_store(struct bus_type *bus, const char *buf,
>> size_t count)
>> {
>> int rc;
>> + unsigned long newaqm[BITS_TO_LONGS(AP_DEVICES)];
>> +
>> + memcpy(newaqm, ap_perms.aqm, AQMASKSIZE);
>> +
>> + rc = ap_parse_mask_str(buf, newaqm, AP_DOMAINS, NULL);
>> + if (rc)
>> + return rc;
>> +
>> + if (mutex_lock_interruptible(&ap_perms_mutex))
>> + return -ERESTARTSYS;
> Please move the lock before the memcpy(newaqm, ...)

Will do.

>> +
>> + rc = aqmask_commit(newaqm);
>> + mutex_unlock(&ap_perms_mutex);
>>
>> - rc = ap_parse_mask_str(buf, ap_perms.aqm, AP_DOMAINS, &ap_perms_mutex);
>> if (rc)
>> return rc;
>>
>> diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h
>> index 6f3cf37776ca..0f865c5545f2 100644
>> --- a/drivers/s390/crypto/ap_bus.h
>> +++ b/drivers/s390/crypto/ap_bus.h
>> @@ -137,6 +137,7 @@ struct ap_driver {
>> void (*remove)(struct ap_device *);
>> void (*suspend)(struct ap_device *);
>> void (*resume)(struct ap_device *);
>> + bool (*in_use)(unsigned long *apm, unsigned long *aqm);
>> };
>>
>> #define to_ap_drv(x) container_of((x), struct ap_driver, driver)
>> @@ -265,6 +266,8 @@ void ap_queue_reinit_state(struct ap_queue *aq);
>> struct ap_card *ap_card_create(int id, int queue_depth, int raw_device_type,
>> int comp_device_type, unsigned int functions);
>>
>> +#define APMASKSIZE (BITS_TO_LONGS(AP_DEVICES) * sizeof(unsigned long))
>> +#define AQMASKSIZE (BITS_TO_LONGS(AP_DOMAINS) * sizeof(unsigned long))
> add one empty line here please
>> struct ap_perms {
>> unsigned long ioctlm[BITS_TO_LONGS(AP_IOCTLS)];
>> unsigned long apm[BITS_TO_LONGS(AP_DEVICES)];
>