thunderbolt: Add support for PCIe tunneling disabled (SL5)

Recent Intel Thunderbolt firmware connection manager has support for
another security level, SL5, that disables PCIe tunneling. This option
can be turned on from the BIOS.

When this is set the driver exposes a new security level "nopcie" to the
userspace and hides the authorized attribute under connected devices.

While there we also hide it when "dponly" security level is enabled
since it is not really usable in that case anyway.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Yehezkel Bernat <YehezkelShB@gmail.com>

Documentation/ABI/testing/sysfs-bus-thunderbolt

@@ -85,6 +85,8 @@ Description:	This attribute holds current Thunderbolt security level
 		usbonly  Automatically tunnel USB controller of the
 			 connected Thunderbolt dock (and Display Port). All
 			 PCIe links downstream of the dock are removed.
+		nopcie   USB4 system where PCIe tunneling is disabled from
+			 the BIOS.
 		=======  ==================================================
 
 What: /sys/bus/thunderbolt/devices/.../authorized

Documentation/admin-guide/thunderbolt.rst

@@ -47,6 +47,9 @@ be DMA masters and thus read contents of the host memory without CPU and OS
 knowing about it. There are ways to prevent this by setting up an IOMMU but
 it is not always available for various reasons.
 
+Some USB4 systems have a BIOS setting to disable PCIe tunneling. This is
+treated as another security level (nopcie).
+
 The security levels are as follows:
 
   none
@@ -77,6 +80,10 @@ The security levels are as follows:
     Display Port in a dock. All PCIe links downstream of the dock are
     removed.
 
+  nopcie
+    PCIe tunneling is disabled/forbidden from the BIOS. Available in some
+    USB4 systems.
+
 The current security level can be read from
 ``/sys/bus/thunderbolt/devices/domainX/security`` where ``domainX`` is
 the Thunderbolt domain the host controller manages. There is typically

drivers/thunderbolt/domain.c

@@ -118,6 +118,7 @@ static const char * const tb_security_names[] = {
 	[TB_SECURITY_SECURE] = "secure",
 	[TB_SECURITY_DPONLY] = "dponly",
 	[TB_SECURITY_USBONLY] = "usbonly",
+	[TB_SECURITY_NOPCIE] = "nopcie",
 };
 
 static ssize_t boot_acl_show(struct device *dev, struct device_attribute *attr,
@@ -243,8 +244,14 @@ static ssize_t deauthorization_show(struct device *dev,
 				    char *buf)
 {
 	const struct tb *tb = container_of(dev, struct tb, dev);
+	bool deauthorization = false;
 
-	return sprintf(buf, "%d\n", !!tb->cm_ops->disapprove_switch);
+	/* Only meaningful if authorization is supported */
+	if (tb->security_level == TB_SECURITY_USER ||
+	    tb->security_level == TB_SECURITY_SECURE)
+		deauthorization = !!tb->cm_ops->disapprove_switch;
+
+	return sprintf(buf, "%d\n", deauthorization);
 }
 static DEVICE_ATTR_RO(deauthorization);
 
@@ -452,6 +459,9 @@ int tb_domain_add(struct tb *tb)
 			goto err_ctl_stop;
 	}
 
+	tb_dbg(tb, "security level set to %s\n",
+	       tb_security_names[tb->security_level]);
+
 	ret = device_add(&tb->dev);
 	if (ret)
 		goto err_ctl_stop;

drivers/thunderbolt/switch.c

@@ -1774,7 +1774,11 @@ static umode_t switch_attr_is_visible(struct kobject *kobj,
 	struct device *dev = kobj_to_dev(kobj);
 	struct tb_switch *sw = tb_to_switch(dev);
 
-	if (attr == &dev_attr_device.attr) {
+	if (attr == &dev_attr_authorized.attr) {
+		if (sw->tb->security_level == TB_SECURITY_NOPCIE ||
+		    sw->tb->security_level == TB_SECURITY_DPONLY)
+			return 0;
+	} else if (attr == &dev_attr_device.attr) {
 		if (!sw->device)
 			return 0;
 	} else if (attr == &dev_attr_device_name.attr) {

include/linux/thunderbolt.h

@@ -45,13 +45,16 @@ enum tb_cfg_pkg_type {
  * @TB_SECURITY_USBONLY: Only tunnel USB controller of the connected
  *			 Thunderbolt dock (and Display Port). All PCIe
  *			 links downstream of the dock are removed.
+ * @TB_SECURITY_NOPCIE: For USB4 systems this level is used when the
+ *			PCIe tunneling is disabled from the BIOS.
  */
 enum tb_security_level {
 	TB_SECURITY_NONE,
 	TB_SECURITY_USER,
 	TB_SECURITY_SECURE,
 	TB_SECURITY_DPONLY,
 	TB_SECURITY_USBONLY,
+	TB_SECURITY_NOPCIE,
 };
 
 /**