1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 *
5 * The "Virtual Machine Generation ID" is exposed via ACPI 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/kernel.h>
11#include <linux/module.h>
12#include <linux/acpi.h>
13#include <linux/random.h>
14
15ACPI_MODULE_NAME("vmgenid");
16
17enum { VMGENID_SIZE = 16 };
18
19struct vmgenid_state {
20	u8 *next_id;
21	u8 this_id[VMGENID_SIZE];
22};
23
24static int vmgenid_add(struct acpi_device *device)
25{
26	struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
27	struct vmgenid_state *state;
28	union acpi_object *obj;
29	phys_addr_t phys_addr;
30	acpi_status status;
31	int ret = 0;
32
33	state = devm_kmalloc(&device->dev, sizeof(*state), GFP_KERNEL);
34	if (!state)
35		return -ENOMEM;
36
37	status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
38	if (ACPI_FAILURE(status)) {
39		ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
40		return -ENODEV;
41	}
42	obj = parsed.pointer;
43	if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 ||
44	    obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
45	    obj->package.elements[1].type != ACPI_TYPE_INTEGER) {
46		ret = -EINVAL;
47		goto out;
48	}
49
50	phys_addr = (obj->package.elements[0].integer.value << 0) |
51		    (obj->package.elements[1].integer.value << 32);
52	state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
53	if (IS_ERR(state->next_id)) {
54		ret = PTR_ERR(state->next_id);
55		goto out;
56	}
57
58	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
59	add_device_randomness(state->this_id, sizeof(state->this_id));
60
61	device->driver_data = state;
62
63out:
64	ACPI_FREE(parsed.pointer);
65	return ret;
66}
67
68static void vmgenid_notify(struct acpi_device *device, u32 event)
69{
70	struct vmgenid_state *state = acpi_driver_data(device);
71	u8 old_id[VMGENID_SIZE];
72
73	memcpy(old_id, state->this_id, sizeof(old_id));
74	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
75	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
76		return;
77	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
78}
79
80static const struct acpi_device_id vmgenid_ids[] = {
81	{ "VMGENCTR", 0 },
82	{ "VM_GEN_COUNTER", 0 },
83	{ }
84};
85
86static struct acpi_driver vmgenid_driver = {
87	.name = "vmgenid",
88	.ids = vmgenid_ids,
89	.owner = THIS_MODULE,
90	.ops = {
91		.add = vmgenid_add,
92		.notify = vmgenid_notify
93	}
94};
95
96module_acpi_driver(vmgenid_driver);
97
98MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
99MODULE_DESCRIPTION("Virtual Machine Generation ID");
100MODULE_LICENSE("GPL v2");
101MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");
102