thunderbolt: Add support for de-authorizing devices

In some cases it is useful to be able de-authorize devices. For example
if user logs out the userspace can have a policy that disconnects PCIe
devices until logged in again. This is only possible for software based
connection manager as it directly controls the tunnels.

For this reason make the authorized attribute accept writing 0 which
makes the software connection manager to tear down the corresponding
PCIe tunnel. Userspace can check if this is supported by reading a new
domain attribute deauthorization, that holds 1 in that case.

While there correct tb_domain_approve_switch() kernel-doc and
description of authorized attribute to mention that it is only about
PCIe tunnels.

Cc: Christian Kellner <christian@kellner.me>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Yehezkel Bernat <YehezkelShB@gmail.com>

Documentation/ABI/testing/sysfs-bus-thunderbolt

@@ -49,6 +49,15 @@ Description:	Holds a comma separated list of device unique_ids that
 		If a device is authorized automatically during boot its
 		boot attribute is set to 1.
 
+What: /sys/bus/thunderbolt/devices/.../domainX/deauthorization
+Date:		May 2021
+KernelVersion:	5.12
+Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
+Description:	This attribute tells whether the system supports
+		de-authorization of devices. Value of 1 means user can
+		de-authorize PCIe tunnel by writing 0 to authorized
+		attribute under each device.
+
 What: /sys/bus/thunderbolt/devices/.../domainX/iommu_dma_protection
 Date:		Mar 2019
 KernelVersion:	4.21
@@ -84,22 +93,25 @@ KernelVersion:	4.13
 Contact:	thunderbolt-software@lists.01.org
 Description:	This attribute is used to authorize Thunderbolt devices
 		after they have been connected. If the device is not
-		authorized, no devices such as PCIe and Display port are
-		available to the system.
+		authorized, no PCIe devices are available to the system.
 
 		Contents of this attribute will be 0 when the device is not
 		yet authorized.
 
 		Possible values are supported:
 
-		==  ===========================================
+		==  ===================================================
+		0   The device will be de-authorized (only supported if
+		    deauthorization attribute under domain contains 1)
 		1   The device will be authorized and connected
-		==  ===========================================
+		==  ===================================================
 
 		When key attribute contains 32 byte hex string the possible
 		values are:
 
 		==  ========================================================
+		0   The device will be de-authorized (only supported if
+		    deauthorization attribute under domain contains 1)
 		1   The 32 byte hex string is added to the device NVM and
 		    the device is authorized.
 		2   Send a challenge based on the 32 byte hex string. If the

Documentation/admin-guide/thunderbolt.rst

@@ -153,6 +153,22 @@ If the user still wants to connect the device they can either approve
 the device without a key or write a new key and write 1 to the
 ``authorized`` file to get the new key stored on the device NVM.
 
+De-authorizing devices
+----------------------
+It is possible to de-authorize devices by writing ``0`` to their
+``authorized`` attribute. This requires support from the connection
+manager implementation and can be checked by reading domain
+``deauthorization`` attribute. If it reads ``1`` then the feature is
+supported.
+
+When a device is de-authorized the PCIe tunnel from the parent device
+PCIe downstream (or root) port to the device PCIe upstream port is torn
+down. This is essentially the same thing as PCIe hot-remove and the PCIe
+toplogy in question will not be accessible anymore until the device is
+authorized again. If there is storage such as NVMe or similar involved,
+there is a risk for data loss if the filesystem on that storage is not
+properly shut down. You have been warned!
+
 DMA protection utilizing IOMMU
 ------------------------------
 Recent systems from 2018 and forward with Thunderbolt ports may natively

drivers/thunderbolt/domain.c

@@ -238,6 +238,16 @@ err_free_str:
 }
 static DEVICE_ATTR_RW(boot_acl);
 
+static ssize_t deauthorization_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	const struct tb *tb = container_of(dev, struct tb, dev);
+
+	return sprintf(buf, "%d\n", !!tb->cm_ops->disapprove_switch);
+}
+static DEVICE_ATTR_RO(deauthorization);
+
 static ssize_t iommu_dma_protection_show(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)
@@ -267,6 +277,7 @@ static DEVICE_ATTR_RO(security);
 
 static struct attribute *domain_attrs[] = {
 	&dev_attr_boot_acl.attr,
+	&dev_attr_deauthorization.attr,
 	&dev_attr_iommu_dma_protection.attr,
 	&dev_attr_security.attr,
 	NULL,
@@ -601,14 +612,31 @@ int tb_domain_runtime_resume(struct tb *tb)
 	return 0;
 }
 
+/**
+ * tb_domain_disapprove_switch() - Disapprove switch
+ * @tb: Domain the switch belongs to
+ * @sw: Switch to disapprove
+ *
+ * This will disconnect PCIe tunnel from parent to this @sw.
+ *
+ * Return: %0 on success and negative errno in case of failure.
+ */
+int tb_domain_disapprove_switch(struct tb *tb, struct tb_switch *sw)
+{
+	if (!tb->cm_ops->disapprove_switch)
+		return -EPERM;
+
+	return tb->cm_ops->disapprove_switch(tb, sw);
+}
+
 /**
  * tb_domain_approve_switch() - Approve switch
  * @tb: Domain the switch belongs to
  * @sw: Switch to approve
  *
  * This will approve switch by connection manager specific means. In
- * case of success the connection manager will create tunnels for all
- * supported protocols.
+ * case of success the connection manager will create PCIe tunnel from
+ * parent to @sw.
  */
 int tb_domain_approve_switch(struct tb *tb, struct tb_switch *sw)
 {

drivers/thunderbolt/switch.c

@@ -1387,6 +1387,30 @@ static ssize_t authorized_show(struct device *dev,
 	return sprintf(buf, "%u\n", sw->authorized);
 }
 
+static int disapprove_switch(struct device *dev, void *not_used)
+{
+	struct tb_switch *sw;
+
+	sw = tb_to_switch(dev);
+	if (sw && sw->authorized) {
+		int ret;
+
+		/* First children */
+		ret = device_for_each_child_reverse(&sw->dev, NULL, disapprove_switch);
+		if (ret)
+			return ret;
+
+		ret = tb_domain_disapprove_switch(sw->tb, sw);
+		if (ret)
+			return ret;
+
+		sw->authorized = 0;
+		kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE);
+	}
+
+	return 0;
+}
+
 static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
 {
 	int ret = -EINVAL;
@@ -1394,10 +1418,18 @@ static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
 	if (!mutex_trylock(&sw->tb->lock))
 		return restart_syscall();
 
-	if (sw->authorized)
+	if (!!sw->authorized == !!val)
 		goto unlock;
 
 	switch (val) {
+	/* Disapprove switch */
+	case 0:
+		if (tb_route(sw)) {
+			ret = disapprove_switch(&sw->dev, NULL);
+			goto unlock;
+		}
+		break;
+
 	/* Approve switch */
 	case 1:
 		if (sw->key)

drivers/thunderbolt/tb.c

@@ -1002,6 +1002,25 @@ static void tb_disconnect_and_release_dp(struct tb *tb)
 	}
 }
 
+static int tb_disconnect_pci(struct tb *tb, struct tb_switch *sw)
+{
+	struct tb_tunnel *tunnel;
+	struct tb_port *up;
+
+	up = tb_switch_find_port(sw, TB_TYPE_PCIE_UP);
+	if (WARN_ON(!up))
+		return -ENODEV;
+
+	tunnel = tb_find_tunnel(tb, TB_TUNNEL_PCI, NULL, up);
+	if (WARN_ON(!tunnel))
+		return -ENODEV;
+
+	tb_tunnel_deactivate(tunnel);
+	list_del(&tunnel->list);
+	tb_tunnel_free(tunnel);
+	return 0;
+}
+
 static int tb_tunnel_pci(struct tb *tb, struct tb_switch *sw)
 {
 	struct tb_port *up, *down, *port;
@@ -1512,6 +1531,7 @@ static const struct tb_cm_ops tb_cm_ops = {
 	.runtime_suspend = tb_runtime_suspend,
 	.runtime_resume = tb_runtime_resume,
 	.handle_event = tb_handle_event,
+	.disapprove_switch = tb_disconnect_pci,
 	.approve_switch = tb_tunnel_pci,
 	.approve_xdomain_paths = tb_approve_xdomain_paths,
 	.disconnect_xdomain_paths = tb_disconnect_xdomain_paths,

drivers/thunderbolt/tb.h

@@ -361,6 +361,7 @@ struct tb_path {
  * @handle_event: Handle thunderbolt event
  * @get_boot_acl: Get boot ACL list
  * @set_boot_acl: Set boot ACL list
+ * @disapprove_switch: Disapprove switch (disconnect PCIe tunnel)
  * @approve_switch: Approve switch
  * @add_switch_key: Add key to switch
  * @challenge_switch_key: Challenge switch using key
@@ -394,6 +395,7 @@ struct tb_cm_ops {
 			     const void *buf, size_t size);
 	int (*get_boot_acl)(struct tb *tb, uuid_t *uuids, size_t nuuids);
 	int (*set_boot_acl)(struct tb *tb, const uuid_t *uuids, size_t nuuids);
+	int (*disapprove_switch)(struct tb *tb, struct tb_switch *sw);
 	int (*approve_switch)(struct tb *tb, struct tb_switch *sw);
 	int (*add_switch_key)(struct tb *tb, struct tb_switch *sw);
 	int (*challenge_switch_key)(struct tb *tb, struct tb_switch *sw,
@@ -629,6 +631,7 @@ int tb_domain_thaw_noirq(struct tb *tb);
 void tb_domain_complete(struct tb *tb);
 int tb_domain_runtime_suspend(struct tb *tb);
 int tb_domain_runtime_resume(struct tb *tb);
+int tb_domain_disapprove_switch(struct tb *tb, struct tb_switch *sw);
 int tb_domain_approve_switch(struct tb *tb, struct tb_switch *sw);
 int tb_domain_approve_switch_key(struct tb *tb, struct tb_switch *sw);
 int tb_domain_challenge_switch_key(struct tb *tb, struct tb_switch *sw);