thunderbolt: Add support for Internal Connection Manager (ICM)

Starting from Intel Falcon Ridge the internal connection manager running
on the Thunderbolt host controller has been supporting 4 security
levels. One reason for this is to prevent DMA attacks and only allow
connecting devices the user trusts.

The internal connection manager (ICM) is the preferred way of connecting
Thunderbolt devices over software only implementation typically used on
Macs. The driver communicates with ICM using special Thunderbolt ring 0
(control channel) messages. In order to handle these messages we add
support for the ICM messages to the control channel.

The security levels are as follows:

  none - No security, all tunnels are created automatically
  user - User needs to approve the device before tunnels are created
  secure - User need to approve the device before tunnels are created.
	   The device is sent a challenge on future connects to be able
	   to verify it is actually the approved device.
  dponly - Only Display Port and USB tunnels can be created and those
           are created automatically.

The security levels are typically configurable from the system BIOS and
by default it is set to "user" on many systems.

In this patch each Thunderbolt device will have either one or two new
sysfs attributes: authorized and key. The latter appears for devices
that support secure connect.

In order to identify the device the user can read identication
information, including UUID and name of the device from sysfs and based
on that make a decision to authorize the device. The device is
authorized by simply writing 1 to the "authorized" sysfs attribute. This
is following the USB bus device authorization mechanism. The secure
connect requires an additional challenge step (writing 2 to the
"authorized" attribute) in future connects when the key has already been
stored to the NVM of the device.

Non-ICM systems (before Alpine Ridge) continue to use the existing
functionality and the security level is set to none. For systems with
Alpine Ridge, even on Apple hardware, we will use ICM.

This code is based on the work done by Amir Levy and Michael Jamet.

Signed-off-by: Michael Jamet <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>
Reviewed-by: Yehezkel Bernat <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Andreas Noever <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: westeri

Documentation/ABI/testing/sysfs-bus-thunderbolt

@@ -1,3 +1,51 @@
+What: /sys/bus/thunderbolt/devices/.../domainX/security
+Date:		Sep 2017
+KernelVersion:	4.13
+Contact:	[email protected]
+Description:	This attribute holds current Thunderbolt security level
+		set by the system BIOS. Possible values are:
+
+		none: All devices are automatically authorized
+		user: Devices are only authorized based on writing
+		      appropriate value to the authorized attribute
+		secure: Require devices that support secure connect at
+			minimum. User needs to authorize each device.
+		dponly: Automatically tunnel Display port (and USB). No
+			PCIe tunnels are created.
+
+What: /sys/bus/thunderbolt/devices/.../authorized
+Date:		Sep 2017
+KernelVersion:	4.13
+Contact:	[email protected]
+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.
+
+		Contents of this attribute will be 0 when the device is not
+		yet authorized.
+
+		Possible values are supported:
+		1: The device will be authorized and connected
+
+		When key attribute contains 32 byte hex string the possible
+		values are:
+		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
+		   challenge response from device is valid, the device is
+		   authorized. In case of failure errno will be ENOKEY if
+		   the device did not contain a key at all, and
+		   EKEYREJECTED if the challenge response did not match.
+
+What: /sys/bus/thunderbolt/devices/.../key
+Date:		Sep 2017
+KernelVersion:	4.13
+Contact:	[email protected]
+Description:	When a devices supports Thunderbolt secure connect it will
+		have this attribute. Writing 32 byte hex string changes
+		authorization to use the secure connection method instead.
+
 What:		/sys/bus/thunderbolt/devices/.../device
 Date:		Sep 2017
 KernelVersion:	4.13

drivers/thunderbolt/Kconfig

@@ -1,15 +1,15 @@
 menuconfig THUNDERBOLT
-	tristate "Thunderbolt support for Apple devices"
+	tristate "Thunderbolt support"
 	depends on PCI
 	depends on X86 || COMPILE_TEST
 	select APPLE_PROPERTIES if EFI_STUB && X86
 	select CRC32
+	select CRYPTO
+	select CRYPTO_HASH
 	help
-	  Cactus Ridge Thunderbolt Controller driver
-	  This driver is required if you want to hotplug Thunderbolt devices on
-	  Apple hardware.
-
-	  Device chaining is currently not supported.
+	  Thunderbolt Controller driver. This driver is required if you
+	  want to hotplug Thunderbolt devices on Apple hardware or on PCs
+	  with Intel Falcon Ridge or newer.
 
 	  To compile this driver a module, choose M here. The module will be
 	  called thunderbolt.

drivers/thunderbolt/Makefile

@@ -1,3 +1,3 @@
 obj-${CONFIG_THUNDERBOLT} := thunderbolt.o
 thunderbolt-objs := nhi.o ctl.o tb.o switch.o cap.o path.o tunnel_pci.o eeprom.o
-thunderbolt-objs += domain.o dma_port.o
+thunderbolt-objs += domain.o dma_port.o icm.o

drivers/thunderbolt/ctl.c

@@ -463,6 +463,8 @@ static void tb_ctl_rx_callback(struct tb_ring *ring, struct ring_frame *frame,
 				   "RX: checksum mismatch, dropping packet\n");
 			goto rx;
 		}
+		/* Fall through */
+	case TB_CFG_PKG_ICM_EVENT:
 		tb_ctl_handle_event(pkg->ctl, frame->eof, pkg, frame->size);
 		goto rx;
 

drivers/thunderbolt/domain.c

@@ -13,11 +13,43 @@
 #include <linux/idr.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/random.h>
+#include <crypto/hash.h>
 
 #include "tb.h"
 
 static DEFINE_IDA(tb_domain_ida);
 
+static const char * const tb_security_names[] = {
+	[TB_SECURITY_NONE] = "none",
+	[TB_SECURITY_USER] = "user",
+	[TB_SECURITY_SECURE] = "secure",
+	[TB_SECURITY_DPONLY] = "dponly",
+};
+
+static ssize_t security_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct tb *tb = container_of(dev, struct tb, dev);
+
+	return sprintf(buf, "%s\n", tb_security_names[tb->security_level]);
+}
+static DEVICE_ATTR_RO(security);
+
+static struct attribute *domain_attrs[] = {
+	&dev_attr_security.attr,
+	NULL,
+};
+
+static struct attribute_group domain_attr_group = {
+	.attrs = domain_attrs,
+};
+
+static const struct attribute_group *domain_attr_groups[] = {
+	&domain_attr_group,
+	NULL,
+};
+
 struct bus_type tb_bus_type = {
 	.name = "thunderbolt",
 };
@@ -82,6 +114,7 @@ struct tb *tb_domain_alloc(struct tb_nhi *nhi, size_t privsize)
 	tb->dev.parent = &nhi->pdev->dev;
 	tb->dev.bus = &tb_bus_type;
 	tb->dev.type = &tb_domain_type;
+	tb->dev.groups = domain_attr_groups;
 	dev_set_name(&tb->dev, "domain%d", tb->index);
 	device_initialize(&tb->dev);
 
@@ -140,6 +173,12 @@ int tb_domain_add(struct tb *tb)
 	 */
 	tb_ctl_start(tb->ctl);
 
+	if (tb->cm_ops->driver_ready) {
+		ret = tb->cm_ops->driver_ready(tb);
+		if (ret)
+			goto err_ctl_stop;
+	}
+
 	ret = device_add(&tb->dev);
 	if (ret)
 		goto err_ctl_stop;
@@ -231,6 +270,162 @@ int tb_domain_resume_noirq(struct tb *tb)
 	return ret;
 }
 
+int tb_domain_suspend(struct tb *tb)
+{
+	int ret;
+
+	mutex_lock(&tb->lock);
+	if (tb->cm_ops->suspend) {
+		ret = tb->cm_ops->suspend(tb);
+		if (ret) {
+			mutex_unlock(&tb->lock);
+			return ret;
+		}
+	}
+	mutex_unlock(&tb->lock);
+	return 0;
+}
+
+void tb_domain_complete(struct tb *tb)
+{
+	mutex_lock(&tb->lock);
+	if (tb->cm_ops->complete)
+		tb->cm_ops->complete(tb);
+	mutex_unlock(&tb->lock);
+}
+
+/**
+ * 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.
+ */
+int tb_domain_approve_switch(struct tb *tb, struct tb_switch *sw)
+{
+	struct tb_switch *parent_sw;
+
+	if (!tb->cm_ops->approve_switch)
+		return -EPERM;
+
+	/* The parent switch must be authorized before this one */
+	parent_sw = tb_to_switch(sw->dev.parent);
+	if (!parent_sw || !parent_sw->authorized)
+		return -EINVAL;
+
+	return tb->cm_ops->approve_switch(tb, sw);
+}
+
+/**
+ * tb_domain_approve_switch_key() - Approve switch and add key
+ * @tb: Domain the switch belongs to
+ * @sw: Switch to approve
+ *
+ * For switches that support secure connect, this function first adds
+ * key to the switch NVM using connection manager specific means. If
+ * adding the key is successful, the switch is approved and connected.
+ *
+ * Return: %0 on success and negative errno in case of failure.
+ */
+int tb_domain_approve_switch_key(struct tb *tb, struct tb_switch *sw)
+{
+	struct tb_switch *parent_sw;
+	int ret;
+
+	if (!tb->cm_ops->approve_switch || !tb->cm_ops->add_switch_key)
+		return -EPERM;
+
+	/* The parent switch must be authorized before this one */
+	parent_sw = tb_to_switch(sw->dev.parent);
+	if (!parent_sw || !parent_sw->authorized)
+		return -EINVAL;
+
+	ret = tb->cm_ops->add_switch_key(tb, sw);
+	if (ret)
+		return ret;
+
+	return tb->cm_ops->approve_switch(tb, sw);
+}
+
+/**
+ * tb_domain_challenge_switch_key() - Challenge and approve switch
+ * @tb: Domain the switch belongs to
+ * @sw: Switch to approve
+ *
+ * For switches that support secure connect, this function generates
+ * random challenge and sends it to the switch. The switch responds to
+ * this and if the response matches our random challenge, the switch is
+ * approved and connected.
+ *
+ * Return: %0 on success and negative errno in case of failure.
+ */
+int tb_domain_challenge_switch_key(struct tb *tb, struct tb_switch *sw)
+{
+	u8 challenge[TB_SWITCH_KEY_SIZE];
+	u8 response[TB_SWITCH_KEY_SIZE];
+	u8 hmac[TB_SWITCH_KEY_SIZE];
+	struct tb_switch *parent_sw;
+	struct crypto_shash *tfm;
+	struct shash_desc *shash;
+	int ret;
+
+	if (!tb->cm_ops->approve_switch || !tb->cm_ops->challenge_switch_key)
+		return -EPERM;
+
+	/* The parent switch must be authorized before this one */
+	parent_sw = tb_to_switch(sw->dev.parent);
+	if (!parent_sw || !parent_sw->authorized)
+		return -EINVAL;
+
+	get_random_bytes(challenge, sizeof(challenge));
+	ret = tb->cm_ops->challenge_switch_key(tb, sw, challenge, response);
+	if (ret)
+		return ret;
+
+	tfm = crypto_alloc_shash("hmac(sha256)", 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	ret = crypto_shash_setkey(tfm, sw->key, TB_SWITCH_KEY_SIZE);
+	if (ret)
+		goto err_free_tfm;
+
+	shash = kzalloc(sizeof(*shash) + crypto_shash_descsize(tfm),
+			GFP_KERNEL);
+	if (!shash) {
+		ret = -ENOMEM;
+		goto err_free_tfm;
+	}
+
+	shash->tfm = tfm;
+	shash->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+
+	memset(hmac, 0, sizeof(hmac));
+	ret = crypto_shash_digest(shash, challenge, sizeof(hmac), hmac);
+	if (ret)
+		goto err_free_shash;
+
+	/* The returned HMAC must match the one we calculated */
+	if (memcmp(response, hmac, sizeof(hmac))) {
+		ret = -EKEYREJECTED;
+		goto err_free_shash;
+	}
+
+	crypto_free_shash(tfm);
+	kfree(shash);
+
+	return tb->cm_ops->approve_switch(tb, sw);
+
+err_free_shash:
+	kfree(shash);
+err_free_tfm:
+	crypto_free_shash(tfm);
+
+	return ret;
+}
+
 int tb_domain_init(void)
 {
 	return bus_register(&tb_bus_type);