[PATCH v4 0/2] Driver for Open Profile for DICE

[PATCH v4 0/2] Driver for Open Profile for DICE

[David Brazdil]

Open Profile for DICE is an open protocol for measured boot compatible
with the Trusted Computing Group's Device Identifier Composition
Engine (DICE) specification. The generated Compound Device Identifier
(CDI) certificates represent the measured hardware/software combination
and can be used by userspace for remote attestation and sealing.

This patchset adds DeviceTree bindings for the DICE device referencing
a reserved memory region containing the CDIs, and a driver that exposes
the memory region to userspace via a misc device.

See https://pigweed.googlesource.com/open-dice for more details.

The patches are based on top of v5.16-rc5 and can also be found here:
  https://android-kvm.googlesource.com/linux topic/dice_v4

Changes since v3:
  * align with semantics of read/write
  * fix kerneldoc warnings
  * fix printf format warnings

Changes since v2:
  * renamed from 'dice' to 'open-dice'
  * replaced ioctls with read/write
  * replaced memzero_explicit with memset
  * allowed multiple instances
  * expanded Kconfig description

Changes since v1:
  * converted to miscdevice
  * all mappings now write-combine to simplify semantics
  * removed atomic state, any attempt at exclusive access
  * simplified wipe, applied on ioctl, not on release
  * fixed ioctl return value

David Brazdil (2):
  dt-bindings: firmware: Add Open Profile for DICE
  misc: open-dice: Add driver to expose DICE data to userspace

 .../bindings/firmware/google,open-dice.yaml   |  51 +++++
 drivers/misc/Kconfig                          |  12 ++
 drivers/misc/Makefile                         |   1 +
 drivers/misc/open-dice.c                      | 197 ++++++++++++++++++
 4 files changed, 261 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/firmware/google,open-dice.yaml
 create mode 100644 drivers/misc/open-dice.c

--
2.34.1.173.g76aa8bc2d0-goog

[PATCH v4 1/2] dt-bindings: firmware: Add Open Profile for DICE

[David Brazdil]

Add DeviceTree bindings for Open Profile for DICE, an open protocol for
measured boot. Firmware uses DICE to measure the hardware/software
combination and generates Compound Device Identifier (CDI) certificates.
These are stored in memory and the buffer is described in the DT as
a reserved memory region referenced by a compatible device node.

Signed-off-by: David Brazdil <dbrazdil@google.com>
---
 .../bindings/firmware/google,open-dice.yaml   | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/firmware/google,open-dice.yaml

diff --git a/Documentation/devicetree/bindings/firmware/google,open-dice.yaml b/Documentation/devicetree/bindings/firmware/google,open-dice.yaml
new file mode 100644
index 000000000000..1aa69f381b8c
--- /dev/null
+++ b/Documentation/devicetree/bindings/firmware/google,open-dice.yaml
@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/firmware/google,open-dice.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Open Profile for DICE Device Tree Bindings
+
+description: |
+  This binding represents a reserved memory region containing data
+  generated by the Open Profile for DICE protocol.
+
+  See https://pigweed.googlesource.com/open-dice/
+
+maintainers:
+  - David Brazdil <dbrazdil@google.com>
+
+properties:
+  compatible:
+    enum:
+      - google,open-dice
+
+  memory-region:
+    maxItems: 1
+    description: |
+      phandle to the reserved memory node to be associated with the device
+      The reserved memory node should be defined as per the bindings,
+      Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
+
+required:
+  - compatible
+  - memory-region
+
+additionalProperties: false
+
+examples:
+  - |
+    reserved-memory {
+        #address-cells = <2>;
+        #size-cells = <1>;
+
+        dice_reserved: dice@12340000 {
+            reg = <0x00 0x12340000 0x2000>;
+            no-map;
+        };
+    };
+
+    dice {
+        compatible = "google,open-dice";
+        memory-region = <&dice_reserved>;
+    };
-- 
2.34.1.173.g76aa8bc2d0-goog

[PATCH v4 2/2] misc: open-dice: Add driver to expose DICE data to userspace

[David Brazdil]

Open Profile for DICE is an open protocol for measured boot compatible
with the Trusted Computing Group's Device Identifier Composition
Engine (DICE) specification. The generated Compound Device Identifier
(CDI) certificates represent the hardware/software combination measured
by DICE, and can be used for remote attestation and sealing.

Add a driver that exposes reserved memory regions populated by firmware
with DICE CDIs and exposes them to userspace via a character device.

Userspace obtains the memory region's size from read() and calls mmap()
to create a mapping of the memory region in its address space. The
mapping is not allowed to be write+shared, giving userspace a guarantee
that the data were not overwritten by another process.

Userspace can also call write(), which triggers a wipe of the DICE data
by the driver. Because both the kernel and userspace mappings use
write-combine semantics, all clients observe the memory as zeroed after
the syscall has returned.

Cc: Andrew Scull <ascull@google.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: David Brazdil <dbrazdil@google.com>
---
 drivers/misc/Kconfig     |  12 +++
 drivers/misc/Makefile    |   1 +
 drivers/misc/open-dice.c | 197 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 210 insertions(+)
 create mode 100644 drivers/misc/open-dice.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 0f5a49fc7c9e..4d996485f5a7 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -470,6 +470,18 @@ config HISI_HIKEY_USB
 	  switching between the dual-role USB-C port and the USB-A host ports
 	  using only one USB controller.
 
+config OPEN_DICE
+	tristate "Open Profile for DICE driver"
+	depends on OF_RESERVED_MEM
+	help
+	  This driver exposes a DICE reserved memory region to userspace via
+	  a character device. The memory region contains Compound Device
+	  Identifiers (CDIs) generated by firmware as an output of DICE
+	  measured boot flow. Userspace can uses CDIs for remote attestation
+	  and sealing.
+
+	  If unsure, say N.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index a086197af544..70e800e9127f 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -59,3 +59,4 @@ obj-$(CONFIG_UACCE)		+= uacce/
 obj-$(CONFIG_XILINX_SDFEC)	+= xilinx_sdfec.o
 obj-$(CONFIG_HISI_HIKEY_USB)	+= hisi_hikey_usb.o
 obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
+obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
diff --git a/drivers/misc/open-dice.c b/drivers/misc/open-dice.c
new file mode 100644
index 000000000000..8ad5f07dcd55
--- /dev/null
+++ b/drivers/misc/open-dice.c
@@ -0,0 +1,197 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 - Google LLC
+ * Author: David Brazdil <dbrazdil@google.com>
+ *
+ * Driver for Open Profile for DICE.
+ *
+ * This driver takes ownership of a reserved memory region containing secrets
+ * derived following the Open Profile for DICE. The contents of the memory
+ * region are not interpreted by the kernel but can be mapped into a userspace
+ * process via a misc device. The memory region can also be wiped, removing
+ * the secrets from memory.
+ *
+ * Userspace can access the data by (w/o error handling):
+ *
+ *     fd = open("/dev/open-dice0", O_RDWR);
+ *     read(fd, &size, sizeof(unsigned long));
+ *     data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+ *     write(fd, NULL, 0); // wipe
+ *     close(fd);
+ */
+
+#include <linux/io.h>
+#include <linux/miscdevice.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/platform_device.h>
+
+#define DRIVER_NAME "open-dice"
+
+struct open_dice_drvdata {
+	spinlock_t lock;
+	char name[16];
+	struct reserved_mem *rmem;
+	struct miscdevice misc;
+};
+
+static inline struct open_dice_drvdata *to_open_dice_drvdata(struct file *filp)
+{
+	return container_of(filp->private_data, struct open_dice_drvdata, misc);
+}
+
+static int open_dice_wipe(struct open_dice_drvdata *drvdata)
+{
+	void *kaddr;
+
+	spin_lock(&drvdata->lock);
+	kaddr = devm_memremap(drvdata->misc.this_device, drvdata->rmem->base,
+			      drvdata->rmem->size, MEMREMAP_WC);
+	if (IS_ERR(kaddr)) {
+		spin_unlock(&drvdata->lock);
+		return PTR_ERR(kaddr);
+	}
+
+	memset(kaddr, 0, drvdata->rmem->size);
+	devm_memunmap(drvdata->misc.this_device, kaddr);
+	spin_unlock(&drvdata->lock);
+	return 0;
+}
+
+/*
+ * Copies the size of the reserved memory region to the user-provided buffer.
+ */
+static ssize_t open_dice_read(struct file *filp, char __user *ptr, size_t len,
+			      loff_t *off)
+{
+	unsigned long val = to_open_dice_drvdata(filp)->rmem->size;
+
+	return simple_read_from_buffer(ptr, len, off, &val, sizeof(val));
+}
+
+/*
+ * Triggers a wipe of the reserved memory region. The user-provided pointer is
+ * never dereferenced.
+ */
+static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
+			       size_t len, loff_t *off)
+{
+	if (open_dice_wipe(to_open_dice_drvdata(filp)))
+		return -EIO;
+
+	/* Consume the buffer. */
+	return len;
+}
+
+/*
+ * Creates a mapping of the reserved memory region in a user address space.
+ */
+static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
+
+	/* Do not allow userspace to modify the underlying data. */
+	if ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & VM_SHARED))
+		return -EPERM;
+
+	/* Create write-combine mapping so all clients observe a wipe. */
+	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+	vma->vm_flags |= VM_DONTCOPY | VM_DONTDUMP;
+	return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size);
+}
+
+static const struct file_operations open_dice_fops = {
+	.owner = THIS_MODULE,
+	.read = open_dice_read,
+	.write = open_dice_write,
+	.mmap = open_dice_mmap,
+};
+
+static int __init open_dice_probe(struct platform_device *pdev)
+{
+	static unsigned int dev_idx;
+	struct device *dev = &pdev->dev;
+	struct device_node *rmem_np;
+	struct reserved_mem *rmem;
+	struct open_dice_drvdata *drvdata;
+	int ret;
+
+	rmem_np = of_parse_phandle(dev->of_node, "memory-region", 0);
+	if (!rmem_np) {
+		dev_err(dev, "missing 'memory-region' property\n");
+		return -EINVAL;
+	}
+
+	rmem = of_reserved_mem_lookup(rmem_np);
+	of_node_put(rmem_np);
+	if (!rmem) {
+		dev_err(dev, "failed to lookup reserved memory\n");
+		return -EINVAL;
+	}
+
+	if (!rmem->size || (rmem->size > ULONG_MAX)) {
+		dev_err(dev, "invalid memory region size\n");
+		return -EINVAL;
+	}
+
+	if (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) {
+		dev_err(dev, "memory region must be page-aligned\n");
+		return -EINVAL;
+	}
+
+	drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	*drvdata = (struct open_dice_drvdata){
+		.lock = __SPIN_LOCK_UNLOCKED(drvdata->lock),
+		.rmem = rmem,
+		.misc = (struct miscdevice){
+			.parent	= dev,
+			.name	= drvdata->name,
+			.minor	= MISC_DYNAMIC_MINOR,
+			.fops	= &open_dice_fops,
+			.mode	= 0600,
+		},
+	};
+
+	/* Index overflow check not needed. misc_register() will fail. */
+	snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++);
+
+	ret = misc_register(&drvdata->misc);
+	if (ret) {
+		dev_err(dev, "failed to register misc device '%s': %d\n",
+			drvdata->name, ret);
+		return ret;
+	}
+
+	platform_set_drvdata(pdev, drvdata);
+	return 0;
+}
+
+static int open_dice_remove(struct platform_device *pdev)
+{
+	struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev);
+
+	misc_deregister(&drvdata->misc);
+	return 0;
+}
+
+static const struct of_device_id open_dice_of_match[] = {
+	{ .compatible = "google,open-dice" },
+	{},
+};
+
+static struct platform_driver open_dice_driver = {
+	.remove = open_dice_remove,
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = open_dice_of_match,
+	},
+};
+
+module_platform_driver_probe(open_dice_driver, open_dice_probe);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>");
-- 
2.34.1.173.g76aa8bc2d0-goog

Re: [PATCH v4 2/2] misc: open-dice: Add driver to expose DICE data to userspace

[Greg Kroah-Hartman]

On Wed, Dec 15, 2021 at 03:04:10PM +0000, David Brazdil wrote:
> +	drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> +	if (!drvdata)
> +		return -ENOMEM;
> +
> +	*drvdata = (struct open_dice_drvdata){
> +		.lock = __SPIN_LOCK_UNLOCKED(drvdata->lock),
> +		.rmem = rmem,
> +		.misc = (struct miscdevice){
> +			.parent	= dev,
> +			.name	= drvdata->name,
> +			.minor	= MISC_DYNAMIC_MINOR,
> +			.fops	= &open_dice_fops,
> +			.mode	= 0600,
> +		},
> +	};

That is a lovely abuse of an implicit memcpy(), took me a while to
realize what it was doing here...

Anyway, this all looks great to me, I'll wait for the DT maintainers to
review the dt change before being able to take this through my tree.
Thanks for the cleanups based on the review, the driver is now almost
1/3 smaller than your first version with more functionality!

thanks,

greg k-h

Re: [PATCH v4 2/2] misc: open-dice: Add driver to expose DICE data to userspace

[David Brazdil]

On Wed, Dec 15, 2021 at 04:19:35PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Dec 15, 2021 at 03:04:10PM +0000, David Brazdil wrote:
> > +	drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> > +	if (!drvdata)
> > +		return -ENOMEM;
> > +
> > +	*drvdata = (struct open_dice_drvdata){
> > +		.lock = __SPIN_LOCK_UNLOCKED(drvdata->lock),
> > +		.rmem = rmem,
> > +		.misc = (struct miscdevice){
> > +			.parent	= dev,
> > +			.name	= drvdata->name,
> > +			.minor	= MISC_DYNAMIC_MINOR,
> > +			.fops	= &open_dice_fops,
> > +			.mode	= 0600,
> > +		},
> > +	};
> 
> That is a lovely abuse of an implicit memcpy(), took me a while to
> realize what it was doing here...
> 
> Anyway, this all looks great to me, I'll wait for the DT maintainers to
> review the dt change before being able to take this through my tree.
> Thanks for the cleanups based on the review, the driver is now almost
> 1/3 smaller than your first version with more functionality!

Thanks, and thank your for your help!

David