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

[Tony Krowiak]

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@xxxxxxxxxxxxx>
---
 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;
+
+	/* 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;
+}
+
+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;
+	}
+
+	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;
+
+	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;
 
@@ -1212,12 +1278,72 @@ 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;
+
+	/* Pin the driver's module code */
+	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, APMASKSIZE);
+
+	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_DOMAINS)];
+
+	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;
+
+	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 15a98a673c5c..b00952d5fdbb 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)
@@ -262,6 +263,8 @@ 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))
 struct ap_perms {
 	unsigned long ioctlm[BITS_TO_LONGS(AP_IOCTLS)];
 	unsigned long apm[BITS_TO_LONGS(AP_DEVICES)];
-- 
2.7.4