GNU Linux-libre 5.19-rc6-gnu
[releases.git] / drivers / misc / open-dice.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2021 - Google LLC
4  * Author: David Brazdil <dbrazdil@google.com>
5  *
6  * Driver for Open Profile for DICE.
7  *
8  * This driver takes ownership of a reserved memory region containing data
9  * generated by the Open Profile for DICE measured boot protocol. The memory
10  * contents are not interpreted by the kernel but can be mapped into a userspace
11  * process via a misc device. Userspace can also request a wipe of the memory.
12  *
13  * Userspace can access the data with (w/o error handling):
14  *
15  *     fd = open("/dev/open-dice0", O_RDWR);
16  *     read(fd, &size, sizeof(unsigned long));
17  *     data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
18  *     write(fd, NULL, 0); // wipe
19  *     close(fd);
20  */
21
22 #include <linux/io.h>
23 #include <linux/miscdevice.h>
24 #include <linux/mm.h>
25 #include <linux/module.h>
26 #include <linux/of_reserved_mem.h>
27 #include <linux/platform_device.h>
28
29 #define DRIVER_NAME "open-dice"
30
31 struct open_dice_drvdata {
32         struct mutex lock;
33         char name[16];
34         struct reserved_mem *rmem;
35         struct miscdevice misc;
36 };
37
38 static inline struct open_dice_drvdata *to_open_dice_drvdata(struct file *filp)
39 {
40         return container_of(filp->private_data, struct open_dice_drvdata, misc);
41 }
42
43 static int open_dice_wipe(struct open_dice_drvdata *drvdata)
44 {
45         void *kaddr;
46
47         mutex_lock(&drvdata->lock);
48         kaddr = devm_memremap(drvdata->misc.this_device, drvdata->rmem->base,
49                               drvdata->rmem->size, MEMREMAP_WC);
50         if (IS_ERR(kaddr)) {
51                 mutex_unlock(&drvdata->lock);
52                 return PTR_ERR(kaddr);
53         }
54
55         memset(kaddr, 0, drvdata->rmem->size);
56         devm_memunmap(drvdata->misc.this_device, kaddr);
57         mutex_unlock(&drvdata->lock);
58         return 0;
59 }
60
61 /*
62  * Copies the size of the reserved memory region to the user-provided buffer.
63  */
64 static ssize_t open_dice_read(struct file *filp, char __user *ptr, size_t len,
65                               loff_t *off)
66 {
67         unsigned long val = to_open_dice_drvdata(filp)->rmem->size;
68
69         return simple_read_from_buffer(ptr, len, off, &val, sizeof(val));
70 }
71
72 /*
73  * Triggers a wipe of the reserved memory region. The user-provided pointer
74  * is never dereferenced.
75  */
76 static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
77                                size_t len, loff_t *off)
78 {
79         if (open_dice_wipe(to_open_dice_drvdata(filp)))
80                 return -EIO;
81
82         /* Consume the input buffer. */
83         return len;
84 }
85
86 /*
87  * Creates a mapping of the reserved memory region in user address space.
88  */
89 static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
90 {
91         struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
92
93         /* Do not allow userspace to modify the underlying data. */
94         if ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & VM_SHARED))
95                 return -EPERM;
96
97         /* Ensure userspace cannot acquire VM_WRITE + VM_SHARED later. */
98         if (vma->vm_flags & VM_WRITE)
99                 vma->vm_flags &= ~VM_MAYSHARE;
100         else if (vma->vm_flags & VM_SHARED)
101                 vma->vm_flags &= ~VM_MAYWRITE;
102
103         /* Create write-combine mapping so all clients observe a wipe. */
104         vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
105         vma->vm_flags |= VM_DONTCOPY | VM_DONTDUMP;
106         return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size);
107 }
108
109 static const struct file_operations open_dice_fops = {
110         .owner = THIS_MODULE,
111         .read = open_dice_read,
112         .write = open_dice_write,
113         .mmap = open_dice_mmap,
114 };
115
116 static int __init open_dice_probe(struct platform_device *pdev)
117 {
118         static unsigned int dev_idx;
119         struct device *dev = &pdev->dev;
120         struct reserved_mem *rmem;
121         struct open_dice_drvdata *drvdata;
122         int ret;
123
124         rmem = of_reserved_mem_lookup(dev->of_node);
125         if (!rmem) {
126                 dev_err(dev, "failed to lookup reserved memory\n");
127                 return -EINVAL;
128         }
129
130         if (!rmem->size || (rmem->size > ULONG_MAX)) {
131                 dev_err(dev, "invalid memory region size\n");
132                 return -EINVAL;
133         }
134
135         if (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) {
136                 dev_err(dev, "memory region must be page-aligned\n");
137                 return -EINVAL;
138         }
139
140         drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL);
141         if (!drvdata)
142                 return -ENOMEM;
143
144         *drvdata = (struct open_dice_drvdata){
145                 .lock = __MUTEX_INITIALIZER(drvdata->lock),
146                 .rmem = rmem,
147                 .misc = (struct miscdevice){
148                         .parent = dev,
149                         .name   = drvdata->name,
150                         .minor  = MISC_DYNAMIC_MINOR,
151                         .fops   = &open_dice_fops,
152                         .mode   = 0600,
153                 },
154         };
155
156         /* Index overflow check not needed, misc_register() will fail. */
157         snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++);
158
159         ret = misc_register(&drvdata->misc);
160         if (ret) {
161                 dev_err(dev, "failed to register misc device '%s': %d\n",
162                         drvdata->name, ret);
163                 return ret;
164         }
165
166         platform_set_drvdata(pdev, drvdata);
167         return 0;
168 }
169
170 static int open_dice_remove(struct platform_device *pdev)
171 {
172         struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev);
173
174         misc_deregister(&drvdata->misc);
175         return 0;
176 }
177
178 static const struct of_device_id open_dice_of_match[] = {
179         { .compatible = "google,open-dice" },
180         {},
181 };
182
183 static struct platform_driver open_dice_driver = {
184         .remove = open_dice_remove,
185         .driver = {
186                 .name = DRIVER_NAME,
187                 .of_match_table = open_dice_of_match,
188         },
189 };
190
191 static int __init open_dice_init(void)
192 {
193         int ret = platform_driver_probe(&open_dice_driver, open_dice_probe);
194
195         /* DICE regions are optional. Succeed even with zero instances. */
196         return (ret == -ENODEV) ? 0 : ret;
197 }
198
199 static void __exit open_dice_exit(void)
200 {
201         platform_driver_unregister(&open_dice_driver);
202 }
203
204 module_init(open_dice_init);
205 module_exit(open_dice_exit);
206
207 MODULE_LICENSE("GPL v2");
208 MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>");