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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2021 - Google LLC
4 * Author: David Brazdil <[email protected]>
5 * Author: Song Guo <[email protected]>
6 *
7 * Driver for Open Profile for DICE.
8 *
9 * This driver takes ownership of a reserved memory region containing data
10 * generated by the Open Profile for DICE measured boot protocol. The memory
11 * contents are not interpreted by the kernel but can be mapped into a userspace
12 * process via a misc device. Userspace can also request a wipe of the memory.
13 *
14 * Userspace can access the data with (w/o error handling):
15 *
16 * fd = open("/dev/open-dice0", O_RDWR);
17 * read(fd, &size, sizeof(unsigned long));
18 * data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
19 * write(fd, NULL, 0); // wipe
20 * close(fd);
21 */
22
23#include <linux/acpi.h>
24#include <linux/io.h>
25#include <linux/miscdevice.h>
26#include <linux/mm.h>
27#include <linux/module.h>
28#include <linux/of_reserved_mem.h>
29#include <linux/platform_device.h>
30
31#define DRIVER_NAME "open-dice"
32
33struct open_dice_drvdata {
34 struct mutex lock;
35 char name[16];
36 phys_addr_t mem_base;
37 resource_size_t mem_size;
38 struct miscdevice misc;
39};
40
41static inline struct open_dice_drvdata *to_open_dice_drvdata(struct file *filp)
42{
43 return container_of(filp->private_data, struct open_dice_drvdata, misc);
44}
45
46static int open_dice_wipe(struct open_dice_drvdata *drvdata)
47{
48 void *kaddr;
49
50 mutex_lock(&drvdata->lock);
51 kaddr = devm_memremap(drvdata->misc.this_device, drvdata->mem_base,
52 drvdata->mem_size, MEMREMAP_WC);
53 if (IS_ERR(kaddr)) {
54 mutex_unlock(&drvdata->lock);
55 return PTR_ERR(kaddr);
56 }
57
58 memset(kaddr, 0, drvdata->mem_size);
59 devm_memunmap(drvdata->misc.this_device, kaddr);
60 mutex_unlock(&drvdata->lock);
61 return 0;
62}
63
64/*
65 * Copies the size of the reserved memory region to the user-provided buffer.
66 */
67static ssize_t open_dice_read(struct file *filp, char __user *ptr, size_t len,
68 loff_t *off)
69{
70 unsigned long val = to_open_dice_drvdata(filp)->mem_size;
71
72 return simple_read_from_buffer(ptr, len, off, &val, sizeof(val));
73}
74
75/*
76 * Triggers a wipe of the reserved memory region. The user-provided pointer
77 * is never dereferenced.
78 */
79static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
80 size_t len, loff_t *off)
81{
82 if (open_dice_wipe(to_open_dice_drvdata(filp)))
83 return -EIO;
84
85 /* Consume the input buffer. */
86 return len;
87}
88
89/*
90 * Creates a mapping of the reserved memory region in user address space.
91 */
92static int open_dice_mmap_prepare(struct vm_area_desc *desc)
93{
94 struct file *filp = desc->file;
95 struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
96
97 if (vma_desc_test(desc, VMA_MAYSHARE_BIT)) {
98 /* Do not allow userspace to modify the underlying data. */
99 if (vma_desc_test(desc, VMA_WRITE_BIT))
100 return -EPERM;
101 /* Ensure userspace cannot acquire VM_WRITE later. */
102 vma_desc_clear_flags(desc, VMA_MAYWRITE_BIT);
103 }
104
105 /* Create write-combine mapping so all clients observe a wipe. */
106 desc->page_prot = pgprot_writecombine(desc->page_prot);
107 vma_desc_set_flags(desc, VMA_DONTCOPY_BIT, VMA_DONTDUMP_BIT);
108 mmap_action_simple_ioremap(desc, drvdata->mem_base,
109 drvdata->mem_size);
110 return 0;
111}
112
113static const struct file_operations open_dice_fops = {
114 .owner = THIS_MODULE,
115 .read = open_dice_read,
116 .write = open_dice_write,
117 .mmap_prepare = open_dice_mmap_prepare,
118};
119
120static int __init open_dice_probe(struct platform_device *pdev)
121{
122 static unsigned int dev_idx;
123 struct device *dev = &pdev->dev;
124 struct open_dice_drvdata *drvdata;
125 phys_addr_t mem_base;
126 resource_size_t mem_size;
127 int ret;
128
129 if (dev->of_node) {
130 struct reserved_mem *rmem = of_reserved_mem_lookup(dev->of_node);
131
132 if (!rmem) {
133 dev_err(dev, "failed to lookup reserved memory\n");
134 return -EINVAL;
135 }
136 mem_base = rmem->base;
137 mem_size = rmem->size;
138 } else if (is_acpi_node(dev->fwnode)) {
139 struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
140
141 if (!res) {
142 dev_err(dev, "failed to get MMIO resource\n");
143 return -EINVAL;
144 }
145 mem_base = res->start;
146 mem_size = resource_size(res);
147 } else {
148 dev_err(dev, "device not supported (no DT or ACPI node)\n");
149 return -EINVAL;
150 }
151
152 if (!mem_size || (mem_size > ULONG_MAX)) {
153 dev_err(dev, "invalid memory region size\n");
154 return -EINVAL;
155 }
156
157 if (!PAGE_ALIGNED(mem_base) || !PAGE_ALIGNED(mem_size)) {
158 dev_err(dev, "memory region must be page-aligned\n");
159 return -EINVAL;
160 }
161
162 drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
163 if (!drvdata)
164 return -ENOMEM;
165
166 *drvdata = (struct open_dice_drvdata){
167 .mem_base = mem_base,
168 .mem_size = mem_size,
169 .misc = (struct miscdevice){
170 .parent = dev,
171 .name = drvdata->name,
172 .minor = MISC_DYNAMIC_MINOR,
173 .fops = &open_dice_fops,
174 .mode = 0600,
175 },
176 };
177 mutex_init(&drvdata->lock);
178
179 /* Index overflow check not needed, misc_register() will fail. */
180 snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++);
181
182 ret = misc_register(&drvdata->misc);
183 if (ret) {
184 dev_err(dev, "failed to register misc device '%s': %d\n",
185 drvdata->name, ret);
186 return ret;
187 }
188
189 platform_set_drvdata(pdev, drvdata);
190 return 0;
191}
192
193static void open_dice_remove(struct platform_device *pdev)
194{
195 struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev);
196
197 misc_deregister(&drvdata->misc);
198}
199
200static const struct of_device_id open_dice_of_match[] = {
201 { .compatible = "google,open-dice" },
202 { }
203};
204
205static struct platform_driver open_dice_driver = {
206 .remove = open_dice_remove,
207 .driver = {
208 .name = DRIVER_NAME,
209 .of_match_table = open_dice_of_match,
210 },
211};
212
213static int __init open_dice_init(void)
214{
215 int ret = platform_driver_probe(&open_dice_driver, open_dice_probe);
216
217 /* DICE regions are optional. Succeed even with zero instances. */
218 return (ret == -ENODEV) ? 0 : ret;
219}
220
221static void __exit open_dice_exit(void)
222{
223 platform_driver_unregister(&open_dice_driver);
224}
225
226module_init(open_dice_init);
227module_exit(open_dice_exit);
228
229MODULE_DESCRIPTION("Driver for Open Profile for DICE.");
230MODULE_LICENSE("GPL v2");
231MODULE_AUTHOR("David Brazdil <[email protected]>");
232MODULE_AUTHOR("Song Guo <[email protected]>");