Re: [PATCH v10 04/16] s390/zcrypt: driver callback to indicate resource in use

Halil Pasic
2020-09-25T09:24:20Z

On Fri, 21 Aug 2020 15:56:04 -0400
Tony Krowiak <akrowiak@linux.ibm.com> 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. The intent of
> this callback is to provide a driver with the means to prevent a root user
> from inadvertently taking a queue away from a matrix mdev and giving it to
> the host while it is assigned to the matrix mdev. The callback will
> be invoked whenever a change to the AP bus's sysfs apmask or aqmask
> attributes would 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 facilitates pass-through of an AP queue to a
> guest. The idea here is that a guest may be administered by a different
> sysadmin than the host and we don't want AP resources to unexpectedly
> disappear from a guest's AP configuration (i.e., adapters, domains and
> control domains assigned to the matrix mdev). This will enforce the proper
> procedure for removing AP resources intended for guest usage which is to
> first unassign them from the matrix mdev, then unbind them from the
> vfio_ap device driver.
>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> drivers/s390/crypto/ap_bus.c | 148 ++++++++++++++++++++++++++++++++---
> drivers/s390/crypto/ap_bus.h | 4 +
> 2 files changed, 142 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
> index 24a1940b829e..db27bd931308 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"
> @@ -889,6 +890,23 @@ static int modify_bitmap(const char *str, unsigned long *bitmap, int bits)
> return 0;
> }
>
> +static int ap_parse_bitmap_str(const char *str, unsigned long *bitmap, int bits,
> + unsigned long *newmap)
> +{
> + unsigned long size;
> + int rc;
> +
> + size = BITS_TO_LONGS(bits)*sizeof(unsigned long);
> + if (*str == '+' || *str == '-') {
> + memcpy(newmap, bitmap, size);
> + rc = modify_bitmap(str, newmap, bits);
> + } else {
> + memset(newmap, 0, size);
> + rc = hex2bitmap(str, newmap, bits);
> + }
> + return rc;
> +}
> +
> int ap_parse_mask_str(const char *str,
> unsigned long *bitmap, int bits,
> struct mutex *lock)
> @@ -908,14 +926,7 @@ int ap_parse_mask_str(const char *str,
> kfree(newmap);
> return -ERESTARTSYS;
> }
> -
> - if (*str == '+' || *str == '-') {
> - memcpy(newmap, bitmap, size);
> - rc = modify_bitmap(str, newmap, bits);
> - } else {
> - memset(newmap, 0, size);
> - rc = hex2bitmap(str, newmap, bits);
> - }
> + rc = ap_parse_bitmap_str(str, bitmap, bits, newmap);
> if (rc == 0)
> memcpy(bitmap, newmap, size);
> mutex_unlock(lock);
> @@ -1107,12 +1118,70 @@ 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;
> +
> + /*
> + * No need to verify whether the driver is using the queues if it is the
> + * default driver.
> + */
> + 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);
> + if (rc)
> + return rc;
> + }

I understand the above asks all the non-default drivers if some of the
queues are 'used'. But AFAIU this reflects the truth ap_drv->in_use()
is only telling us something about a given moment...

> +
> + memcpy(ap_perms.apm, newapm, APMASKSIZE);

... So I fail to understand what will prevent us from performing a
successful commit if some of the resources become 'used' between
the call to the in_use() callback and the memcpy.

Of course I might be wrong.

BTW I was never a fan of this mechanism, so I don't mind if it
does not work perfectly, and this should catch most of the cases. Just
want to make sure we don't introduce more confusion than necessary.

> +
> + return 0;
> +}
> +
> static ssize_t apmask_store(struct bus_type *bus, const char *buf,
> size_t count)
> {
> int rc;
> + DECLARE_BITMAP(newapm, AP_DEVICES);
> +
> + if (mutex_lock_interruptible(&ap_perms_mutex))
> + return -ERESTARTSYS;
> +
> + rc = ap_parse_bitmap_str(buf, ap_perms.apm, AP_DEVICES, newapm);
> + if (rc)
> + goto done;
>
> - rc = ap_parse_mask_str(buf, ap_perms.apm, AP_DEVICES, &ap_perms_mutex);
> + rc = apmask_commit(newapm);
> +
> +done:
> + mutex_unlock(&ap_perms_mutex);
> if (rc)
> return rc;
>
> @@ -1138,12 +1207,71 @@ static ssize_t aqmask_show(struct bus_type *bus, char *buf)
> return rc;
> }
>
> +static 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);
> + if (rc)
> + return rc;
> + }
> +
> + memcpy(ap_perms.aqm, newaqm, AQMASKSIZE);
> +

Same here.

Regards,
Halil

> + return 0;
> +}
> +
> static ssize_t aqmask_store(struct bus_type *bus, const char *buf,
> size_t count)
> {
> int rc;
> + DECLARE_BITMAP(newaqm, AP_DOMAINS);
>
> - rc = ap_parse_mask_str(buf, ap_perms.aqm, AP_DOMAINS, &ap_perms_mutex);
> + if (mutex_lock_interruptible(&ap_perms_mutex))
> + return -ERESTARTSYS;
> +
> + rc = ap_parse_bitmap_str(buf, ap_perms.aqm, AP_DOMAINS, newaqm);
> + if (rc)
> + goto done;
> +
> + rc = aqmask_commit(newaqm);
> +
> +done:
> + mutex_unlock(&ap_perms_mutex);
> if (rc)
> return rc;
>
> diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h
> index 1ea046324e8f..48c57b3d53a0 100644
> --- a/drivers/s390/crypto/ap_bus.h
> +++ b/drivers/s390/crypto/ap_bus.h
> @@ -136,6 +136,7 @@ struct ap_driver {
>
> int (*probe)(struct ap_device *);
> void (*remove)(struct ap_device *);
> + bool (*in_use)(unsigned long *apm, unsigned long *aqm);
> };
>
> #define to_ap_drv(x) container_of((x), struct ap_driver, driver)
> @@ -255,6 +256,9 @@ void ap_queue_init_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))
> +
> struct ap_perms {
> unsigned long ioctlm[BITS_TO_LONGS(AP_IOCTLS)];
> unsigned long apm[BITS_TO_LONGS(AP_DEVICES)];