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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2022 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
4 *
5 * The "Virtual Machine Generation ID" is exposed via ACPI or DT and changes when a
6 * virtual machine forks or is cloned. This driver exists for shepherding that
7 * information to random.c.
8 */
9
10#include <linux/acpi.h>
11#include <linux/interrupt.h>
12#include <linux/kernel.h>
13#include <linux/module.h>
14#include <linux/platform_device.h>
15#include <linux/random.h>
16
17ACPI_MODULE_NAME("vmgenid");
18
19enum { VMGENID_SIZE = 16 };
20
21struct vmgenid_state {
22 u8 *next_id;
23 u8 this_id[VMGENID_SIZE];
24};
25
26static void vmgenid_notify(struct device *device)
27{
28 struct vmgenid_state *state = dev_get_drvdata(device);
29 u8 old_id[VMGENID_SIZE];
30
31 memcpy(old_id, state->this_id, sizeof(old_id));
32 memcpy(state->this_id, state->next_id, sizeof(state->this_id));
33 if (!memcmp(old_id, state->this_id, sizeof(old_id)))
34 return;
35 add_vmfork_randomness(state->this_id, sizeof(state->this_id));
36}
37
38static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
39{
40 state->next_id = virt_addr;
41 memcpy(state->this_id, state->next_id, sizeof(state->this_id));
42 add_device_randomness(state->this_id, sizeof(state->this_id));
43}
44
45#ifdef CONFIG_ACPI
46static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
47 u32 __always_unused event, void *dev)
48{
49 vmgenid_notify(dev);
50}
51
52static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
53{
54 struct acpi_device *device = ACPI_COMPANION(dev);
55 struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
56 union acpi_object *obj;
57 phys_addr_t phys_addr;
58 acpi_status status;
59 void *virt_addr;
60 int ret = 0;
61
62 status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
63 if (ACPI_FAILURE(status)) {
64 ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
65 return -ENODEV;
66 }
67 obj = parsed.pointer;
68 if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 ||
69 obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
70 obj->package.elements[1].type != ACPI_TYPE_INTEGER) {
71 ret = -EINVAL;
72 goto out;
73 }
74
75 phys_addr = (obj->package.elements[0].integer.value << 0) |
76 (obj->package.elements[1].integer.value << 32);
77
78 virt_addr = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE,
79 MEMREMAP_WB | MEMREMAP_DEC);
80 if (IS_ERR(virt_addr)) {
81 ret = PTR_ERR(virt_addr);
82 goto out;
83 }
84 setup_vmgenid_state(state, virt_addr);
85
86 dev_set_drvdata(dev, state);
87
88 status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
89 vmgenid_acpi_handler, dev);
90 if (ACPI_FAILURE(status)) {
91 ret = -ENODEV;
92 goto out;
93 }
94
95out:
96 ACPI_FREE(parsed.pointer);
97 return ret;
98}
99#else
100static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
101{
102 return -EINVAL;
103}
104#endif
105
106static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev)
107{
108 vmgenid_notify(dev);
109 return IRQ_HANDLED;
110}
111
112static int vmgenid_add_of(struct platform_device *pdev,
113 struct vmgenid_state *state)
114{
115 void *virt_addr;
116 int ret;
117
118 virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
119 if (IS_ERR(virt_addr))
120 return PTR_ERR(virt_addr);
121
122 setup_vmgenid_state(state, virt_addr);
123
124 ret = platform_get_irq(pdev, 0);
125 if (ret < 0)
126 return ret;
127
128 dev_set_drvdata(&pdev->dev, state);
129
130 ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler,
131 IRQF_SHARED, "vmgenid", &pdev->dev);
132 if (ret < 0)
133 return ret;
134
135 return 0;
136}
137
138static int vmgenid_add(struct platform_device *pdev)
139{
140 struct device *dev = &pdev->dev;
141 struct vmgenid_state *state;
142 int ret;
143
144 state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL);
145 if (!state)
146 return -ENOMEM;
147
148 if (dev->of_node)
149 ret = vmgenid_add_of(pdev, state);
150 else
151 ret = vmgenid_add_acpi(dev, state);
152
153 if (ret < 0)
154 devm_kfree(dev, state);
155 return ret;
156}
157
158static const struct of_device_id vmgenid_of_ids[] = {
159 { .compatible = "microsoft,vmgenid", },
160 { },
161};
162MODULE_DEVICE_TABLE(of, vmgenid_of_ids);
163
164static const struct acpi_device_id vmgenid_acpi_ids[] = {
165 { "VMGENCTR", 0 },
166 { "VM_GEN_COUNTER", 0 },
167 { }
168};
169MODULE_DEVICE_TABLE(acpi, vmgenid_acpi_ids);
170
171static struct platform_driver vmgenid_plaform_driver = {
172 .probe = vmgenid_add,
173 .driver = {
174 .name = "vmgenid",
175 .acpi_match_table = vmgenid_acpi_ids,
176 .of_match_table = vmgenid_of_ids,
177 },
178};
179
180module_platform_driver(vmgenid_plaform_driver)
181
182MODULE_DESCRIPTION("Virtual Machine Generation ID");
183MODULE_LICENSE("GPL v2");
184MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");