Re: [PATCH v2] drivers/tpm: add xen tpmfront interface

[Konrad Rzeszutek Wilk]

On Thu, Apr 11, 2013 at 10:56:01AM -0400, Daniel De Graaf wrote:
> This is a complete rewrite of the Xen TPM frontend driver, taking
> advantage of a simplified frontend/backend interface and adding support
> for cancellation and timeouts.  The backend for this driver is provided
> by a vTPM stub domain using the interface in Xen 4.3.
> 
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> Acked-by: Matthew Fioravante <matthew.fioravante@xxxxxxxxxx>
> ---
> 
> Changes from v1:
>  - Add locality sysfs attribute
> 
>  Documentation/xen-tpmfront.txt   | 116 ++++++++++
>  drivers/char/tpm/Kconfig         |  11 +
>  drivers/char/tpm/Makefile        |   1 +
>  drivers/char/tpm/xen-tpmfront.c  | 460 +++++++++++++++++++++++++++++++++++++++
>  include/xen/interface/io/tpmif.h |  50 +++++
>  5 files changed, 638 insertions(+)
>  create mode 100644 Documentation/xen-tpmfront.txt
>  create mode 100644 drivers/char/tpm/xen-tpmfront.c
>  create mode 100644 include/xen/interface/io/tpmif.h
> 
> diff --git a/Documentation/xen-tpmfront.txt b/Documentation/xen-tpmfront.txt
> new file mode 100644
> index 0000000..8a61d6f
> --- /dev/null
> +++ b/Documentation/xen-tpmfront.txt
> @@ -0,0 +1,116 @@
> +Copyright (c) 2010-2012 United States Government, as represented by
> +the Secretary of Defense.  All rights reserved.
> +November 12 2012
> +Authors: Matthew Fioravante (JHUAPL), Daniel De Graaf (NSA)
> +
> +This document describes the virtual Trusted Platform Module (vTPM) subsystem for
> +Xen. The reader is assumed to have familiarity with building and installing Xen,
> +Linux, and a basic understanding of the TPM and vTPM concepts.
> +
> +------------------------------
> +INTRODUCTION
> +------------------------------
> +
> +The goal of this work is to provide a TPM functionality to a virtual guest
> +operating system (in Xen terms, a DomU).  This allows programs to interact with
> +a TPM in a virtual system the same way they interact with a TPM on the physical
> +system.  Each guest gets its own unique, emulated, software TPM.  However, each
> +of the vTPM's secrets (Keys, NVRAM, etc) are managed by a vTPM Manager domain,
> +which seals the secrets to the Physical TPM.  If the process of creating each of
> +these domains (manager, vTPM, and guest) is trusted, the vTPM subsystem extends
> +the chain of trust rooted in the hardware TPM to virtual machines in Xen. Each
> +major component of vTPM is implemented as a separate domain, providing secure
> +separation guaranteed by the hypervisor. The vTPM domains are implemented in
> +mini-os to reduce memory and processor overhead.
> +
> +This mini-os vTPM subsystem was built on top of the previous vTPM work done by
> +IBM and Intel corporation.
> +
> +------------------------------
> +DESIGN OVERVIEW
> +------------------------------
> +
> +The architecture of vTPM is described below:
> +
> ++------------------+
> +|    Linux DomU    | ...
> +|       |  ^       |
> +|       v  |       |
> +|   xen-tpmfront   |
> ++------------------+
> +        |  ^
> +        v  |
> ++------------------+
> +| mini-os/tpmback  |
> +|       |  ^       |
> +|       v  |       |
> +|  vtpm-stubdom    | ...
> +|       |  ^       |
> +|       v  |       |
> +| mini-os/tpmfront |
> ++------------------+
> +        |  ^
> +        v  |
> ++------------------+
> +| mini-os/tpmback  |
> +|       |  ^       |
> +|       v  |       |
> +| vtpmmgr-stubdom  |
> +|       |  ^       |
> +|       v  |       |
> +| mini-os/tpm_tis  |
> ++------------------+
> +        |  ^
> +        v  |
> ++------------------+
> +|   Hardware TPM   |
> ++------------------+
> +
> + * Linux DomU: The Linux based guest that wants to use a vTPM. There many be
> +	       more than one of these.
> +
> + * xen-tpmfront.ko: Linux kernel virtual TPM frontend driver. This driver
> +                    provides vTPM access to a Linux-based DomU.
> +
> + * mini-os/tpmback: Mini-os TPM backend driver. The Linux frontend driver
> +		    connects to this backend driver to facilitate communications
> +		    between the Linux DomU and its vTPM. This driver is also
> +		    used by vtpmmgr-stubdom to communicate with vtpm-stubdom.
> +
> + * vtpm-stubdom: A mini-os stub domain that implements a vTPM. There is a
> +		 one to one mapping between running vtpm-stubdom instances and
> +                 logical vtpms on the system. The vTPM Platform Configuration
> +                 Registers (PCRs) are normally all initialized to zero.
> +
> + * mini-os/tpmfront: Mini-os TPM frontend driver. The vTPM mini-os domain
> +		     vtpm-stubdom uses this driver to communicate with
> +		     vtpmmgr-stubdom. This driver is also used in mini-os
> +		     domains such as pv-grub that talk to the vTPM domain.
> +
> + * vtpmmgr-stubdom: A mini-os domain that implements the vTPM manager. There is
> +		    only one vTPM manager and it should be running during the
> +		    entire lifetime of the machine.  This domain regulates
> +		    access to the physical TPM on the system and secures the
> +		    persistent state of each vTPM.
> +
> + * mini-os/tpm_tis: Mini-os TPM version 1.2 TPM Interface Specification (TIS)
> +                    driver. This driver used by vtpmmgr-stubdom to talk directly to
> +                    the hardware TPM. Communication is facilitated by mapping
> +                    hardware memory pages into vtpmmgr-stubdom.
> +
> + * Hardware TPM: The physical TPM that is soldered onto the motherboard.
> +
> +------------------------------
> +INTEGRATION WITH XEN
> +------------------------------
> +
> +Support for the vTPM driver was added in Xen using the libxl toolstack in Xen
> +4.3.  See the Xen documentation (docs/misc/vtpm.txt) for details on setting up
> +the vTPM and vTPM Manager stub domains.  Once the stub domains are running, a
> +vTPM device is set up in the same manner as a disk or network device in the
> +domain's configuration file.
> +
> +In order to use features such as IMA that require a TPM to be loaded prior to
> +the initrd, the xen-tpmfront driver must be compiled in to the kernel.  If not
> +using such features, the driver can be compiled as a module and will be loaded
> +as usual.
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index dbfd564..205ed35 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -91,4 +91,15 @@ config TCG_ST33_I2C
>          To compile this driver as a module, choose M here; the module will be
>          called tpm_stm_st33_i2c.
>  
> +config TCG_XEN
> +	tristate "XEN TPM Interface"
> +	depends on TCG_TPM && XEN
> +	---help---
> +	  If you want to make TPM support available to a Xen user domain,
> +	  say Yes and it will be accessible from within Linux. See
> +	  the manpages for xl, xl.conf, and docs/misc/vtpm.txt in
> +	  the Xen source repository for more details.
> +	  To compile this driver as a module, choose M here; the module
> +	  will be called xen-tpmfront.
> +
>  endif # TCG_TPM
> diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
> index a3736c9..eb41ff9 100644
> --- a/drivers/char/tpm/Makefile
> +++ b/drivers/char/tpm/Makefile
> @@ -18,3 +18,4 @@ obj-$(CONFIG_TCG_ATMEL) += tpm_atmel.o
>  obj-$(CONFIG_TCG_INFINEON) += tpm_infineon.o
>  obj-$(CONFIG_TCG_IBMVTPM) += tpm_ibmvtpm.o
>  obj-$(CONFIG_TCG_ST33_I2C) += tpm_i2c_stm_st33.o
> +obj-$(CONFIG_TCG_XEN) += xen-tpmfront.o
> diff --git a/drivers/char/tpm/xen-tpmfront.c b/drivers/char/tpm/xen-tpmfront.c
> new file mode 100644
> index 0000000..6801937
> --- /dev/null
> +++ b/drivers/char/tpm/xen-tpmfront.c
> @@ -0,0 +1,460 @@
> +/*
> + * Implementation of the Xen vTPM device frontend
> + *
> + * Author:  Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2,
> + * as published by the Free Software Foundation.
> + */
> +#include <linux/errno.h>
> +#include <linux/err.h>
> +#include <linux/interrupt.h>
> +#include <xen/events.h>
> +#include <xen/interface/io/tpmif.h>
> +#include <xen/grant_table.h>
> +#include <xen/xenbus.h>
> +#include <xen/page.h>
> +#include "tpm.h"
> +
> +struct tpm_private {
> +	struct tpm_chip *chip;
> +	struct xenbus_device *dev;
> +
> +	struct vtpm_shared_page *shr;
> +
> +	unsigned int evtchn;
> +	int ring_ref;
> +	domid_t backend_id;
> +};
> +
> +enum status_bits {
> +	VTPM_STATUS_RUNNING  = 0x1,
> +	VTPM_STATUS_IDLE     = 0x2,
> +	VTPM_STATUS_RESULT   = 0x4,
> +	VTPM_STATUS_CANCELED = 0x8,
> +};
> +
> +static u8 vtpm_status(struct tpm_chip *chip)
> +{
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	switch (priv->shr->state) {
> +	case VTPM_STATE_IDLE:
> +		return VTPM_STATUS_IDLE | VTPM_STATUS_CANCELED;
> +	case VTPM_STATE_FINISH:
> +		return VTPM_STATUS_IDLE | VTPM_STATUS_RESULT;
> +	case VTPM_STATE_SUBMIT:
> +	case VTPM_STATE_CANCEL: /* cancel requested, not yet canceled */
> +		return VTPM_STATUS_RUNNING;
> +	default:
> +		return 0;
> +	}
> +}
> +
> +static bool vtpm_req_canceled(struct tpm_chip *chip, u8 status)
> +{
> +	return status & VTPM_STATUS_CANCELED;
> +}
> +
> +static void vtpm_cancel(struct tpm_chip *chip)
> +{
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	priv->shr->state = VTPM_STATE_CANCEL;

Don't you need to follow this with a wmb()?

Is it OK to just write the state in the shared memory ? What if there
are other states in it?

What if it has been cancelled before and has VTPM_STATE_CANCEL? Are
the multiple event channel notifications OK? Can the backend handle
spurious frontends?

> +	notify_remote_via_evtchn(priv->evtchn);
> +}
> +
> +static int vtpm_send(struct tpm_chip *chip, u8 *buf, size_t count)
> +{
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	struct vtpm_shared_page *shr = priv->shr;
> +	unsigned int offset = sizeof(*shr) + 4*shr->nr_extra_pages;

The '4' is a bit odd.  Could you use 'sizeof(uint32)' instead?
And perhaps a comment: /* Look in the vtpm_shared_page for details. */

> +
> +	u32 ordinal;
> +	unsigned long duration;
> +
> +	if (count < TPM_HEADER_SIZE)
> +		return -EIO;
> +

Perhaps add a comment saying, "/* Unimplemented. Is possible
but we don't do it yet. */

> +	if (offset > PAGE_SIZE)
> +		return -EIO;
> +
> +	if (offset + count > PAGE_SIZE)
> +		return -EIO;
> +
> +	/* Wait for completion of any existing command or cancellation */
> +	if (wait_for_tpm_stat(chip, VTPM_STATUS_IDLE, chip->vendor.timeout_c,
> +			&chip->vendor.read_queue, true) < 0) {
> +		vtpm_cancel(chip);
> +		return -ETIME;
> +	}
> +
> +	memcpy(offset + (u8 *)shr, buf, count);
> +	shr->length = count;
> +	barrier();

So the barrier is to make sure that 'lenght' is updated before 'state' right?
> +	shr->state = VTPM_STATE_SUBMIT;

You probably want a 'wmb()' here too.

> +	notify_remote_via_evtchn(priv->evtchn);
> +
> +	ordinal = be32_to_cpu(*((__be32 *) (buf + 6)));

Um, + 6? Why? Is there an #define for that magic constant?
Should this value be read before you do the wait_for_tpm_stat stuff?

> +	duration = tpm_calc_ordinal_duration(chip, ordinal);
> +
> +	if (wait_for_tpm_stat(chip, VTPM_STATUS_IDLE, duration,
> +			&chip->vendor.read_queue, true) < 0) {
> +		/* got a signal or timeout, try to cancel */
> +		vtpm_cancel(chip);
> +		return -ETIME;
> +	}
> +
> +	return count;
> +}
> +
> +static int vtpm_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> +{
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	struct vtpm_shared_page *shr = priv->shr;
> +	unsigned int offset = sizeof(*shr) + 4*shr->nr_extra_pages;

Again, the '4'. sizeof(uint32_t).

> +	size_t length = shr->length;
> +
> +	if (shr->state == VTPM_STATE_IDLE)
> +		return -ECANCELED;
> +
> +	/* In theory the wait at the end of _send makes this one unnecessary */
> +	if (wait_for_tpm_stat(chip, VTPM_STATUS_RESULT, chip->vendor.timeout_c,
> +			&chip->vendor.read_queue, true) < 0) {
> +		vtpm_cancel(chip);
> +		return -ETIME;
> +	}
> +
> +	if (offset > PAGE_SIZE)
> +		return -EIO;
> +
> +	if (offset + length > PAGE_SIZE)
> +		length = PAGE_SIZE - offset;
> +
> +	if (length > count)
> +		length = count;
> +
> +	memcpy(buf, offset + (u8 *)shr, count);

s/count/length in that memcpy?

> +
> +	return length;
> +}
> +
> +ssize_t tpm_show_locality(struct device *dev, struct device_attribute *attr,
> +			  char *buf)
> +{
> +	struct tpm_chip *chip = dev_get_drvdata(dev);
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	u8 locality = priv->shr->locality;
> +
> +	return sprintf(buf, "%d\n", locality);
> +}
> +
> +ssize_t tpm_store_locality(struct device *dev, struct device_attribute *attr,
> +			const char *buf, size_t len)
> +{
> +	struct tpm_chip *chip = dev_get_drvdata(dev);
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	u8 val;
> +
> +	int rv = kstrtou8(buf, 0, &val);
> +	if (rv)
> +		return rv;
> +
> +	priv->shr->locality = val;
> +
> +	return len;
> +}
> +
> +static const struct file_operations vtpm_ops = {
> +	.owner = THIS_MODULE,
> +	.llseek = no_llseek,
> +	.open = tpm_open,
> +	.read = tpm_read,
> +	.write = tpm_write,
> +	.release = tpm_release,
> +};
> +
> +static DEVICE_ATTR(pubek, S_IRUGO, tpm_show_pubek, NULL);
> +static DEVICE_ATTR(pcrs, S_IRUGO, tpm_show_pcrs, NULL);
> +static DEVICE_ATTR(enabled, S_IRUGO, tpm_show_enabled, NULL);
> +static DEVICE_ATTR(active, S_IRUGO, tpm_show_active, NULL);
> +static DEVICE_ATTR(owned, S_IRUGO, tpm_show_owned, NULL);
> +static DEVICE_ATTR(temp_deactivated, S_IRUGO, tpm_show_temp_deactivated,
> +		NULL);
> +static DEVICE_ATTR(caps, S_IRUGO, tpm_show_caps, NULL);
> +static DEVICE_ATTR(cancel, S_IWUSR | S_IWGRP, NULL, tpm_store_cancel);
> +static DEVICE_ATTR(durations, S_IRUGO, tpm_show_durations, NULL);
> +static DEVICE_ATTR(timeouts, S_IRUGO, tpm_show_timeouts, NULL);
> +static DEVICE_ATTR(locality, S_IRUGO | S_IWUSR, tpm_show_locality,
> +		tpm_store_locality);
> +
> +static struct attribute *vtpm_attrs[] = {
> +	&dev_attr_pubek.attr,
> +	&dev_attr_pcrs.attr,
> +	&dev_attr_enabled.attr,
> +	&dev_attr_active.attr,
> +	&dev_attr_owned.attr,
> +	&dev_attr_temp_deactivated.attr,
> +	&dev_attr_caps.attr,
> +	&dev_attr_cancel.attr,
> +	&dev_attr_durations.attr,
> +	&dev_attr_timeouts.attr,
> +	&dev_attr_locality.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group vtpm_attr_grp = {
> +	.attrs = vtpm_attrs


Missing an ',' at the end.
> +};
> +
> +#define TPM_LONG_TIMEOUT   (10 * 60 * HZ)

Why this number and not say 1000*60*HZ ?

> +
> +static const struct tpm_vendor_specific tpm_vtpm = {
> +	.status = vtpm_status,
> +	.recv = vtpm_recv,
> +	.send = vtpm_send,
> +	.cancel = vtpm_cancel,
> +	.req_complete_mask = VTPM_STATUS_IDLE | VTPM_STATUS_RESULT,
> +	.req_complete_val  = VTPM_STATUS_IDLE | VTPM_STATUS_RESULT,
> +	.req_canceled      = vtpm_req_canceled,
> +	.attr_group = &vtpm_attr_grp,
> +	.miscdev = {
> +		.fops = &vtpm_ops,
> +	},
> +	.duration = {
> +		TPM_LONG_TIMEOUT,
> +		TPM_LONG_TIMEOUT,
> +		TPM_LONG_TIMEOUT,
> +	},
> +};
> +
> +static irqreturn_t tpmif_interrupt(int dummy, void *dev_id)
> +{
> +	struct tpm_private *priv = dev_id;
> +
> +	switch (priv->shr->state) {
> +	case VTPM_STATE_IDLE:
> +	case VTPM_STATE_FINISH:
> +		wake_up_interruptible(&priv->chip->vendor.read_queue);
> +		break;
> +	case VTPM_STATE_SUBMIT:
> +	case VTPM_STATE_CANCEL:
> +	default:
> +		break;
> +	}
> +	return IRQ_HANDLED;
> +}
> +
> +static int setup_chip(struct device *dev, struct tpm_private *priv)
> +{
> +	struct tpm_chip *chip;
> +
> +	chip = tpm_register_hardware(dev, &tpm_vtpm);
> +	if (!chip)
> +		return -ENODEV;
> +
> +	init_waitqueue_head(&chip->vendor.read_queue);
> +
> +	priv->chip = chip;
> +	TPM_VPRIV(chip) = priv;
> +
> +	return 0;
> +}
> +

Can you add a comment here saying that the caller is responsible for cleaning up
in case of errors please?

> +static int setup_ring(struct xenbus_device *dev, struct tpm_private *priv)
> +{
> +	struct xenbus_transaction xbt;
> +	const char *message = NULL;
> +	int rv;
> +
> +	priv->shr = (void *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
> +	if (!priv->shr) {
> +		xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
> +		return -ENOMEM;
> +	}
> +
> +	rv = xenbus_grant_ring(dev, virt_to_mfn(priv->shr));
> +	if (rv < 0)
> +		return rv;
> +
> +	priv->ring_ref = rv;
> +
> +	rv = xenbus_alloc_evtchn(dev, &priv->evtchn);
> +	if (rv)
> +		return rv;
> +
> +	rv = bind_evtchn_to_irqhandler(priv->evtchn, tpmif_interrupt, 0,
> +				       "tpmif", priv);
> +	if (rv <= 0) {
> +		xenbus_dev_fatal(dev, rv, "allocating TPM irq");
> +		return rv;
> +	}
> +	priv->chip->vendor.irq = rv;
> +
> + again:
> +	rv = xenbus_transaction_start(&xbt);
> +	if (rv) {
> +		xenbus_dev_fatal(dev, rv, "starting transaction");
> +		return rv;
> +	}
> +
> +	rv = xenbus_printf(xbt, dev->nodename,
> +			"ring-ref", "%u", priv->ring_ref);
> +	if (rv) {
> +		message = "writing ring-ref";
> +		goto abort_transaction;
> +	}
> +
> +	rv = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
> +			priv->evtchn);
> +	if (rv) {
> +		message = "writing event-channel";
> +		goto abort_transaction;
> +	}
> +
> +	rv = xenbus_printf(xbt, dev->nodename, "feature-protocol-v2", "1");
> +	if (rv) {
> +		message = "writing feature-protocol-v2";
> +		goto abort_transaction;
> +	}
> +
> +	rv = xenbus_transaction_end(xbt, 0);
> +	if (rv == -EAGAIN)
> +		goto again;
> +	if (rv) {
> +		xenbus_dev_fatal(dev, rv, "completing transaction");
> +		return rv;
> +	}
> +
> +	xenbus_switch_state(dev, XenbusStateInitialised);
> +
> +	return 0;
> +
> + abort_transaction:
> +	xenbus_transaction_end(xbt, 1);
> +	if (message)
> +		xenbus_dev_error(dev, rv, "%s", message);
> +
> +	return rv;
> +}
> +
> +static void ring_free(struct tpm_private *priv)
> +{

A for priv being valid? Say

	if (!priv)
		return;

> +	if (priv->ring_ref)
> +		gnttab_end_foreign_access(priv->ring_ref, 0,
> +				(unsigned long)priv->shr);
> +
> +	if (priv->chip && priv->chip->vendor.irq)
> +		unbind_from_irqhandler(priv->chip->vendor.irq, priv);
> +
> +	free_page((unsigned long)priv->shr);

I think you are missing a call to xenbus_free_evtchn ?

> +	kfree(priv);
> +}
> +
> +static int tpmfront_probe(struct xenbus_device *dev,
> +		const struct xenbus_device_id *id)
> +{
> +	struct tpm_private *priv;
> +	int rv;
> +
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv) {
> +		xenbus_dev_fatal(dev, -ENOMEM, "allocating priv structure");
> +		return -ENOMEM;
> +	}
> +
> +	rv = setup_chip(&dev->dev, priv);
> +	if (rv) {
> +		kfree(priv);
> +		return rv;
> +	}
> +
> +	rv = setup_ring(dev, priv);
> +	if (rv) {
> +		tpm_remove_hardware(&dev->dev);
> +		ring_free(priv);
> +		return rv;
> +	}
> +
> +	tpm_get_timeouts(priv->chip);
> +
> +	dev_set_drvdata(&dev->dev, priv->chip);
> +
> +	return rv;
> +}
> +
> +static int tpmfront_remove(struct xenbus_device *dev)
> +{
> +	struct tpm_chip *chip = dev_get_drvdata(&dev->dev);
> +	struct tpm_private *priv = TPM_VPRIV(chip);
> +	tpm_remove_hardware(&dev->dev);
> +	ring_free(priv);


Perhaps also:
	priv = NULL; ?

> +	return 0;
> +}
> +
> +static int tpmfront_resume(struct xenbus_device *dev)
> +{
> +	/* A suspend/resume/migrate will interrupt a vTPM anyway */
> +	tpmfront_remove(dev);
> +	return tpmfront_probe(dev, NULL);
> +}
> +
> +static void backend_changed(struct xenbus_device *dev,
> +		enum xenbus_state backend_state)
> +{
> +	int val;
> +
> +	switch (backend_state) {
> +	case XenbusStateInitialised:
> +	case XenbusStateConnected:
> +		if (xenbus_scanf(XBT_NIL, dev->otherend,
> +				"feature-protocol-v2", "%d", &val) < 0)
> +			val = 0;
> +		if (!val) {
> +			xenbus_dev_fatal(dev, -EINVAL,
> +					"vTPM protocol 2 required");
> +			return;
> +		}
> +		xenbus_switch_state(dev, XenbusStateConnected);
> +		break;
> +
> +	case XenbusStateClosing:
> +	case XenbusStateClosed:
> +		device_unregister(&dev->dev);
> +		xenbus_frontend_closed(dev);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
> +static const struct xenbus_device_id tpmfront_ids[] = {
> +	{ "vtpm" },
> +	{ "" }
> +};
> +MODULE_ALIAS("xen:vtpm");
> +
> +static DEFINE_XENBUS_DRIVER(tpmfront, ,
> +		.probe = tpmfront_probe,
> +		.remove = tpmfront_remove,
> +		.resume = tpmfront_resume,
> +		.otherend_changed = backend_changed,
> +	);
> +
> +static int __init xen_tpmfront_init(void)
> +{
> +	if (!xen_domain())
> +		return -ENODEV;
> +
> +	return xenbus_register_frontend(&tpmfront_driver);
> +}
> +module_init(xen_tpmfront_init);
> +
> +static void __exit xen_tpmfront_exit(void)
> +{
> +	xenbus_unregister_driver(&tpmfront_driver);
> +}
> +module_exit(xen_tpmfront_exit);
> +
> +MODULE_AUTHOR("Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Xen vTPM Driver");
> +MODULE_LICENSE("GPL");
> diff --git a/include/xen/interface/io/tpmif.h b/include/xen/interface/io/tpmif.h
> new file mode 100644
> index 0000000..92522a4
> --- /dev/null
> +++ b/include/xen/interface/io/tpmif.h
> @@ -0,0 +1,50 @@
> +/******************************************************************************
> + * tpmif.h
> + *
> + * TPM I/O interface for Xen guest OSes, v2
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this software and associated documentation files (the "Software"), to
> + * deal in the Software without restriction, including without limitation the
> + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
> + * sell copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> + * DEALINGS IN THE SOFTWARE.
> + *
> + */
> +
> +#ifndef __XEN_PUBLIC_IO_TPMIF_H__
> +#define __XEN_PUBLIC_IO_TPMIF_H__
> +
> +enum vtpm_shared_page_state {
> +	VTPM_STATE_IDLE,         /* no contents / vTPM idle / cancel complete */
> +	VTPM_STATE_SUBMIT,       /* request ready / vTPM working */
> +	VTPM_STATE_FINISH,       /* response ready / vTPM idle */
> +	VTPM_STATE_CANCEL,       /* cancel requested / vTPM working */
> +};
> +/* The backend should only change state to IDLE or FINISH, while the
> + * frontend should only change to SUBMIT or CANCEL. */
> +
> +
> +struct vtpm_shared_page {
> +	uint32_t length;         /* request/response length in bytes */
> +
> +	uint8_t state;           /* enum vtpm_shared_page_state */
> +	uint8_t locality;        /* for the current request */
> +	uint8_t pad;
> +
> +	uint8_t nr_extra_pages;  /* extra pages for long packets; may be zero */
> +	uint32_t extra_pages[0]; /* grant IDs; length in nr_extra_pages */
> +};
> +
> +#endif
> -- 
> 1.8.1.4
>

Otherwise it looks OK to me. Should this go through me or Kent? 
And if so, is Kent waiting for my feedback?
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