misc: dice: Add driver to forward secrets to userspace
Open Profile for DICE is a protocol for deriving unique secrets at boot,
used by some Android devices. The firmware/bootloader hands over secrets
in a reserved memory region, this driver takes ownership of the memory
region and exposes it to userspace via a character device that
lets userspace mmap the memory region into its process.
The character device can only be opened once at any given time.
Userspace can issue an ioctl requesting that the memory be wiped after
the current FD is released. In that case, the driver will clear
the buffer and refuse to open any new FDs.
Signed-off-by: David Brazdil <dbrazdil@google.com>
diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index cfe6ccc..4b8bee2 100644
--- a/Documentation/userspace-api/ioctl/ioctl-number.rst
+++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
@@ -341,6 +341,7 @@
0xAE 40-FF linux/kvm.h Kernel-based Virtual Machine
<mailto:kvm@vger.kernel.org>
0xAE 20-3F linux/nitro_enclaves.h Nitro Enclaves
+0xAE 40-5F uapi/linux/dice.h Open Profile for DICE driver
0xAF 00-1F linux/fsl_hypervisor.h Freescale hypervisor
0xB0 all RATIO devices in development:
<mailto:vgo@ratio.de>
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 0f5a49f..7165f4b 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -470,6 +470,14 @@
switching between the dual-role USB-C port and the USB-A host ports
using only one USB controller.
+config DICE
+ tristate "Open Profile for DICE driver"
+ depends on OF_RESERVED_MEM
+ help
+ This driver allows to ownership of a reserved memory region
+ containing DICE secrets and expose them to userspace via
+ a character device.
+
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 a086197..f73c6bb 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -59,3 +59,4 @@
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_DICE) += dice.o
diff --git a/drivers/misc/dice.c b/drivers/misc/dice.c
new file mode 100644
index 0000000..c521779
--- /dev/null
+++ b/drivers/misc/dice.c
@@ -0,0 +1,254 @@
+// 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 character device. The memory region can also be wiped, removing
+ * the secrets from memory.
+ *
+ * Userspace can access the data by (w/o error handling):
+ *
+ * int fd = open("/dev/dice", O_RDONLY | O_CLOEXEC);
+ * size_t size = ioctl(fd, DICE_GET_SIZE);
+ * ioctl(fd, DICE_SET_WIPE_ON_CLOSE);
+ * void *data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+ * close(fd);
+ */
+
+#include <linux/cdev.h>
+#include <linux/dice.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/platform_device.h>
+
+#define DICE_MKDEV MKDEV(MAJOR(dice_devt), 0)
+#define DICE_MINOR_COUNT 1
+
+enum dice_state {
+ DICE_STATE_READY = 0,
+ DICE_STATE_BUSY,
+ DICE_STATE_BUSY_WIPE_ON_CLOSE,
+ DICE_STATE_WIPED,
+};
+
+struct dice_data {
+ struct device *dev;
+ struct cdev cdev;
+ atomic_t state;
+ phys_addr_t base;
+ size_t size;
+};
+
+static dev_t dice_devt;
+static struct class *dice_class;
+
+static int dice_open(struct inode *inode, struct file *filp)
+{
+ struct dice_data *data;
+
+ data = container_of(inode->i_cdev, struct dice_data, cdev);
+
+ /* Never allow write access. */
+ if (filp->f_mode & FMODE_WRITE)
+ return -EROFS;
+
+ switch (atomic_cmpxchg(&data->state, DICE_STATE_READY, DICE_STATE_BUSY)) {
+ case DICE_STATE_READY:
+ break;
+ case DICE_STATE_WIPED:
+ /* Return error to inform caller memory has been wiped. */
+ return -EACCES;
+ default:
+ return -EBUSY;
+ }
+
+ filp->private_data = data;
+ nonseekable_open(inode, filp);
+ return 0;
+}
+
+static int dice_release(struct inode *inode, struct file *filp)
+{
+ struct dice_data *data = filp->private_data;
+ void *base;
+
+ if (atomic_read(&data->state) == DICE_STATE_BUSY_WIPE_ON_CLOSE) {
+ base = devm_memremap(data->dev, data->base, data->size, MEMREMAP_WT);
+ if (!WARN_ON(!base)) {
+ memzero_explicit(base, data->size);
+ devm_memunmap(data->dev, base);
+ }
+ atomic_set(&data->state, DICE_STATE_WIPED);
+ return 0;
+ }
+
+ atomic_set(&data->state, DICE_STATE_READY);
+ return 0;
+}
+
+static int dice_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ struct dice_data *data = filp->private_data;
+
+ vma->vm_flags |= VM_DONTCOPY;
+ return vm_iomap_memory(vma, data->base, data->size);
+}
+
+static long dice_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+ struct dice_data *data = filp->private_data;
+
+ switch (cmd) {
+ case DICE_GET_SIZE:
+ /* Checked against INT_MAX in dice_probe(). */
+ return data->size;
+ case DICE_SET_WIPE_ON_CLOSE:
+ atomic_set(&data->state, DICE_STATE_BUSY_WIPE_ON_CLOSE);
+ return 0;
+ }
+
+ return -EINVAL;
+}
+
+static const struct file_operations dice_fops = {
+ .open = dice_open,
+ .release = dice_release,
+ .mmap = dice_mmap,
+ .unlocked_ioctl = dice_ioctl,
+ .llseek = no_llseek,
+};
+
+static int __init dice_probe(struct platform_device *pdev)
+{
+ struct device *chr_dev, *dev = &pdev->dev;
+ struct device_node *rmem_np;
+ struct reserved_mem *rmem;
+ struct dice_data *data;
+ 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 (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) {
+ dev_err(dev, "memory region must be page-aligned\n");
+ return -EINVAL;
+ }
+
+ if (rmem->size > INT_MAX) {
+ dev_err(dev, "memory region too large\n");
+ return -EINVAL;
+ }
+
+ data = devm_kmalloc(dev, sizeof(*data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ *data = (struct dice_data){
+ .dev = dev,
+ .base = rmem->base,
+ .size = rmem->size,
+ .state = ATOMIC_INIT(DICE_STATE_READY),
+ };
+
+ cdev_init(&data->cdev, &dice_fops);
+ data->cdev.owner = THIS_MODULE;
+ ret = cdev_add(&data->cdev, DICE_MKDEV, 1);
+ if (ret)
+ return ret;
+
+ chr_dev = device_create(dice_class, dev, DICE_MKDEV, NULL, "dice");
+ if (IS_ERR(chr_dev)) {
+ cdev_del(&data->cdev);
+ return PTR_ERR(chr_dev);
+ }
+
+ platform_set_drvdata(pdev, data);
+ return 0;
+}
+
+static int dice_remove(struct platform_device *pdev)
+{
+ struct dice_data *data = platform_get_drvdata(pdev);
+
+ cdev_del(&data->cdev);
+ device_destroy(dice_class, DICE_MKDEV);
+ return 0;
+}
+
+static char *dice_devnode(struct device *dev, umode_t *mode)
+{
+ /* Initial permissions: read-only by owner */
+ if (mode)
+ *mode = 0400;
+ return NULL;
+}
+
+static const struct of_device_id dice_of_match[] = {
+ { .compatible = "google,dice" },
+ {},
+};
+
+static struct platform_driver dice_driver = {
+ .remove = dice_remove,
+ .driver = {
+ .name = "dice",
+ .of_match_table = dice_of_match,
+ },
+};
+
+static int __init dice_init(void)
+{
+ int ret;
+
+ ret = alloc_chrdev_region(&dice_devt, 0, DICE_MINOR_COUNT, "dice");
+ if (ret)
+ return ret;
+
+ dice_class = class_create(THIS_MODULE, "dice");
+ if (IS_ERR(dice_class)) {
+ ret = PTR_ERR(dice_class);
+ goto fail;
+ }
+ dice_class->devnode = dice_devnode;
+
+ ret = platform_driver_probe(&dice_driver, dice_probe);
+ if (ret)
+ goto fail;
+
+ return 0;
+
+fail:
+ class_destroy(dice_class);
+ unregister_chrdev_region(dice_devt, DICE_MINOR_COUNT);
+ return ret;
+}
+
+static void __exit dice_exit(void)
+{
+ platform_driver_unregister(&dice_driver);
+ class_destroy(dice_class);
+ unregister_chrdev_region(dice_devt, DICE_MINOR_COUNT);
+}
+
+module_init(dice_init);
+module_exit(dice_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>");
diff --git a/include/uapi/linux/dice.h b/include/uapi/linux/dice.h
new file mode 100644
index 0000000..19d679c
--- /dev/null
+++ b/include/uapi/linux/dice.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * IOCTLs for Open Profile for DICE character device
+ */
+
+#ifndef _UAPI_DICE_H_
+#define _UAPI_DICE_H_
+
+#include <linux/ioctl.h>
+
+#define DICE_GET_SIZE _IO(0xAE, 0x40)
+#define DICE_SET_WIPE_ON_CLOSE _IO(0xAE, 0x41)
+
+#endif
