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209 lines
5.4 KiB
C
209 lines
5.4 KiB
C
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2021 - Google LLC
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* Author: David Brazdil <dbrazdil@google.com>
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*
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* Driver for Open Profile for DICE.
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*
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* This driver takes ownership of a reserved memory region containing data
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* generated by the Open Profile for DICE measured boot protocol. The memory
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* contents are not interpreted by the kernel but can be mapped into a userspace
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* process via a misc device. Userspace can also request a wipe of the memory.
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*
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* Userspace can access the data with (w/o error handling):
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*
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* fd = open("/dev/open-dice0", O_RDWR);
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* read(fd, &size, sizeof(unsigned long));
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* data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
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* write(fd, NULL, 0); // wipe
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* close(fd);
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*/
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#include <linux/io.h>
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#include <linux/miscdevice.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/of_reserved_mem.h>
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#include <linux/platform_device.h>
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#define DRIVER_NAME "open-dice"
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struct open_dice_drvdata {
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struct mutex lock;
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char name[16];
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struct reserved_mem *rmem;
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struct miscdevice misc;
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};
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static inline struct open_dice_drvdata *to_open_dice_drvdata(struct file *filp)
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{
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return container_of(filp->private_data, struct open_dice_drvdata, misc);
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}
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static int open_dice_wipe(struct open_dice_drvdata *drvdata)
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{
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void *kaddr;
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mutex_lock(&drvdata->lock);
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kaddr = devm_memremap(drvdata->misc.this_device, drvdata->rmem->base,
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drvdata->rmem->size, MEMREMAP_WC);
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if (IS_ERR(kaddr)) {
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mutex_unlock(&drvdata->lock);
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return PTR_ERR(kaddr);
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}
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memset(kaddr, 0, drvdata->rmem->size);
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devm_memunmap(drvdata->misc.this_device, kaddr);
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mutex_unlock(&drvdata->lock);
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return 0;
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}
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/*
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* Copies the size of the reserved memory region to the user-provided buffer.
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*/
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static ssize_t open_dice_read(struct file *filp, char __user *ptr, size_t len,
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loff_t *off)
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{
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unsigned long val = to_open_dice_drvdata(filp)->rmem->size;
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return simple_read_from_buffer(ptr, len, off, &val, sizeof(val));
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}
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/*
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* Triggers a wipe of the reserved memory region. The user-provided pointer
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* is never dereferenced.
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*/
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static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
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size_t len, loff_t *off)
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{
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if (open_dice_wipe(to_open_dice_drvdata(filp)))
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return -EIO;
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/* Consume the input buffer. */
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return len;
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}
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/*
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* Creates a mapping of the reserved memory region in user address space.
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*/
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static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
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{
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struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
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/* Do not allow userspace to modify the underlying data. */
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if ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & VM_SHARED))
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return -EPERM;
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/* Ensure userspace cannot acquire VM_WRITE + VM_SHARED later. */
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if (vma->vm_flags & VM_WRITE)
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vma->vm_flags &= ~VM_MAYSHARE;
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else if (vma->vm_flags & VM_SHARED)
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vma->vm_flags &= ~VM_MAYWRITE;
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/* Create write-combine mapping so all clients observe a wipe. */
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vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
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vma->vm_flags |= VM_DONTCOPY | VM_DONTDUMP;
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return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size);
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}
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static const struct file_operations open_dice_fops = {
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.owner = THIS_MODULE,
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.read = open_dice_read,
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.write = open_dice_write,
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.mmap = open_dice_mmap,
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};
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static int __init open_dice_probe(struct platform_device *pdev)
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{
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static unsigned int dev_idx;
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struct device *dev = &pdev->dev;
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struct reserved_mem *rmem;
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struct open_dice_drvdata *drvdata;
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int ret;
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rmem = of_reserved_mem_lookup(dev->of_node);
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if (!rmem) {
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dev_err(dev, "failed to lookup reserved memory\n");
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return -EINVAL;
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}
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if (!rmem->size || (rmem->size > ULONG_MAX)) {
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dev_err(dev, "invalid memory region size\n");
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return -EINVAL;
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}
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if (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) {
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dev_err(dev, "memory region must be page-aligned\n");
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return -EINVAL;
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}
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drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
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if (!drvdata)
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return -ENOMEM;
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*drvdata = (struct open_dice_drvdata){
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.lock = __MUTEX_INITIALIZER(drvdata->lock),
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.rmem = rmem,
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.misc = (struct miscdevice){
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.parent = dev,
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.name = drvdata->name,
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.minor = MISC_DYNAMIC_MINOR,
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.fops = &open_dice_fops,
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.mode = 0600,
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},
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};
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/* Index overflow check not needed, misc_register() will fail. */
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snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++);
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ret = misc_register(&drvdata->misc);
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if (ret) {
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dev_err(dev, "failed to register misc device '%s': %d\n",
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drvdata->name, ret);
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return ret;
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}
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platform_set_drvdata(pdev, drvdata);
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return 0;
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}
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static int open_dice_remove(struct platform_device *pdev)
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{
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struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev);
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misc_deregister(&drvdata->misc);
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return 0;
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}
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static const struct of_device_id open_dice_of_match[] = {
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{ .compatible = "google,open-dice" },
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{},
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};
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static struct platform_driver open_dice_driver = {
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.remove = open_dice_remove,
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.driver = {
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.name = DRIVER_NAME,
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.of_match_table = open_dice_of_match,
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},
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};
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static int __init open_dice_init(void)
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{
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int ret = platform_driver_probe(&open_dice_driver, open_dice_probe);
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/* DICE regions are optional. Succeed even with zero instances. */
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return (ret == -ENODEV) ? 0 : ret;
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}
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static void __exit open_dice_exit(void)
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{
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platform_driver_unregister(&open_dice_driver);
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}
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module_init(open_dice_init);
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module_exit(open_dice_exit);
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MODULE_LICENSE("GPL v2");
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MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>");
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