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// 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);
if (vma->vm_flags & VM_MAYSHARE) {
/* Do not allow userspace to modify the underlying data. */
if (vma->vm_flags & VM_WRITE)
return -EPERM;
/* Ensure userspace cannot acquire VM_WRITE later. */
vm_flags_clear(vma, VM_MAYWRITE);
}
/* Create write-combine mapping so all clients observe a wipe. */
vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
vm_flags_set(vma, 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){
.rmem = rmem,
.misc = (struct miscdevice){
.parent = dev,
.name = drvdata->name,
.minor = MISC_DYNAMIC_MINOR,
.fops = &open_dice_fops,
.mode = 0600,
},
};
mutex_init(&drvdata->lock);
/* 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>");
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