Commit | Line | Data |
---|---|---|
f396eded DB |
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 | ||
997931ce DH |
93 | if (vma->vm_flags & VM_MAYSHARE) { |
94 | /* Do not allow userspace to modify the underlying data. */ | |
95 | if (vma->vm_flags & VM_WRITE) | |
96 | return -EPERM; | |
97 | /* Ensure userspace cannot acquire VM_WRITE later. */ | |
1c71222e | 98 | vm_flags_clear(vma, VM_MAYWRITE); |
997931ce | 99 | } |
f396eded DB |
100 | |
101 | /* Create write-combine mapping so all clients observe a wipe. */ | |
102 | vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); | |
1c71222e | 103 | vm_flags_set(vma, VM_DONTCOPY | VM_DONTDUMP); |
f396eded DB |
104 | return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size); |
105 | } | |
106 | ||
107 | static const struct file_operations open_dice_fops = { | |
108 | .owner = THIS_MODULE, | |
109 | .read = open_dice_read, | |
110 | .write = open_dice_write, | |
111 | .mmap = open_dice_mmap, | |
112 | }; | |
113 | ||
114 | static int __init open_dice_probe(struct platform_device *pdev) | |
115 | { | |
116 | static unsigned int dev_idx; | |
117 | struct device *dev = &pdev->dev; | |
118 | struct reserved_mem *rmem; | |
119 | struct open_dice_drvdata *drvdata; | |
120 | int ret; | |
121 | ||
122 | rmem = of_reserved_mem_lookup(dev->of_node); | |
123 | if (!rmem) { | |
124 | dev_err(dev, "failed to lookup reserved memory\n"); | |
125 | return -EINVAL; | |
126 | } | |
127 | ||
128 | if (!rmem->size || (rmem->size > ULONG_MAX)) { | |
129 | dev_err(dev, "invalid memory region size\n"); | |
130 | return -EINVAL; | |
131 | } | |
132 | ||
133 | if (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) { | |
134 | dev_err(dev, "memory region must be page-aligned\n"); | |
135 | return -EINVAL; | |
136 | } | |
137 | ||
138 | drvdata = devm_kmalloc(dev, sizeof(*drvdata), GFP_KERNEL); | |
139 | if (!drvdata) | |
140 | return -ENOMEM; | |
141 | ||
142 | *drvdata = (struct open_dice_drvdata){ | |
143 | .lock = __MUTEX_INITIALIZER(drvdata->lock), | |
144 | .rmem = rmem, | |
145 | .misc = (struct miscdevice){ | |
146 | .parent = dev, | |
147 | .name = drvdata->name, | |
148 | .minor = MISC_DYNAMIC_MINOR, | |
149 | .fops = &open_dice_fops, | |
150 | .mode = 0600, | |
151 | }, | |
152 | }; | |
153 | ||
154 | /* Index overflow check not needed, misc_register() will fail. */ | |
155 | snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++); | |
156 | ||
157 | ret = misc_register(&drvdata->misc); | |
158 | if (ret) { | |
159 | dev_err(dev, "failed to register misc device '%s': %d\n", | |
160 | drvdata->name, ret); | |
161 | return ret; | |
162 | } | |
163 | ||
164 | platform_set_drvdata(pdev, drvdata); | |
165 | return 0; | |
166 | } | |
167 | ||
168 | static int open_dice_remove(struct platform_device *pdev) | |
169 | { | |
170 | struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev); | |
171 | ||
172 | misc_deregister(&drvdata->misc); | |
173 | return 0; | |
174 | } | |
175 | ||
176 | static const struct of_device_id open_dice_of_match[] = { | |
177 | { .compatible = "google,open-dice" }, | |
178 | {}, | |
179 | }; | |
180 | ||
181 | static struct platform_driver open_dice_driver = { | |
182 | .remove = open_dice_remove, | |
183 | .driver = { | |
184 | .name = DRIVER_NAME, | |
185 | .of_match_table = open_dice_of_match, | |
186 | }, | |
187 | }; | |
188 | ||
189 | static int __init open_dice_init(void) | |
190 | { | |
191 | int ret = platform_driver_probe(&open_dice_driver, open_dice_probe); | |
192 | ||
193 | /* DICE regions are optional. Succeed even with zero instances. */ | |
194 | return (ret == -ENODEV) ? 0 : ret; | |
195 | } | |
196 | ||
197 | static void __exit open_dice_exit(void) | |
198 | { | |
199 | platform_driver_unregister(&open_dice_driver); | |
200 | } | |
201 | ||
202 | module_init(open_dice_init); | |
203 | module_exit(open_dice_exit); | |
204 | ||
205 | MODULE_LICENSE("GPL v2"); | |
206 | MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>"); |