diff options
Diffstat (limited to 'drivers/misc/open-dice.c')
| -rw-r--r-- | drivers/misc/open-dice.c | 208 |
1 files changed, 208 insertions, 0 deletions
diff --git a/drivers/misc/open-dice.c b/drivers/misc/open-dice.c new file mode 100644 index 000000000000..c61be3404c6f --- /dev/null +++ b/drivers/misc/open-dice.c @@ -0,0 +1,208 @@ +// 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 data + * generated by the Open Profile for DICE measured boot protocol. The memory + * contents are not interpreted by the kernel but can be mapped into a userspace + * process via a misc device. Userspace can also request a wipe of the memory. + * + * Userspace can access the data with (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 { + struct mutex 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; + + mutex_lock(&drvdata->lock); + kaddr = devm_memremap(drvdata->misc.this_device, drvdata->rmem->base, + drvdata->rmem->size, MEMREMAP_WC); + if (IS_ERR(kaddr)) { + mutex_unlock(&drvdata->lock); + return PTR_ERR(kaddr); + } + + memset(kaddr, 0, drvdata->rmem->size); + devm_memunmap(drvdata->misc.this_device, kaddr); + mutex_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 input buffer. */ + return len; +} + +/* + * Creates a mapping of the reserved memory region in 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; + + /* Ensure userspace cannot acquire VM_WRITE + VM_SHARED later. */ + if (vma->vm_flags & VM_WRITE) + vma->vm_flags &= ~VM_MAYSHARE; + else if (vma->vm_flags & VM_SHARED) + vma->vm_flags &= ~VM_MAYWRITE; + + /* 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 reserved_mem *rmem; + struct open_dice_drvdata *drvdata; + int ret; + + rmem = of_reserved_mem_lookup(dev->of_node); + 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 = __MUTEX_INITIALIZER(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, + }, +}; + +static int __init open_dice_init(void) +{ + int ret = platform_driver_probe(&open_dice_driver, open_dice_probe); + + /* DICE regions are optional. Succeed even with zero instances. */ + return (ret == -ENODEV) ? 0 : ret; +} + +static void __exit open_dice_exit(void) +{ + platform_driver_unregister(&open_dice_driver); +} + +module_init(open_dice_init); +module_exit(open_dice_exit); + +MODULE_LICENSE("GPL v2"); +MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>"); |