1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
|
// 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){
.lock = __MUTEX_INITIALIZER(drvdata->lock),
.rmem = rmem,
.misc = (struct miscdevice){
.parent = dev,
.name = drvdata->name,
.minor = MISC_DYNAMIC_MINOR,
.fops = &open_dice_fops,
.mode = 0600,
},
};
/* 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>");
|
