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 | |
15 | ACPI_MODULE_NAME("vmgenid" ); |
16 | |
17 | enum { VMGENID_SIZE = 16 }; |
18 | |
19 | struct vmgenid_state { |
20 | u8 *next_id; |
21 | u8 this_id[VMGENID_SIZE]; |
22 | }; |
23 | |
24 | static 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(dev: &device->dev, size: sizeof(*state), GFP_KERNEL); |
34 | if (!state) |
35 | return -ENOMEM; |
36 | |
37 | status = acpi_evaluate_object(object: device->handle, pathname: "ADDR" , NULL, return_object_buffer: &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(dev: &device->dev, offset: phys_addr, size: VMGENID_SIZE, flags: MEMREMAP_WB); |
53 | if (IS_ERR(ptr: state->next_id)) { |
54 | ret = PTR_ERR(ptr: state->next_id); |
55 | goto out; |
56 | } |
57 | |
58 | memcpy(state->this_id, state->next_id, sizeof(state->this_id)); |
59 | add_device_randomness(buf: state->this_id, len: sizeof(state->this_id)); |
60 | |
61 | device->driver_data = state; |
62 | |
63 | out: |
64 | ACPI_FREE(parsed.pointer); |
65 | return ret; |
66 | } |
67 | |
68 | static void vmgenid_notify(struct acpi_device *device, u32 event) |
69 | { |
70 | struct vmgenid_state *state = acpi_driver_data(d: 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(p: old_id, q: state->this_id, size: sizeof(old_id))) |
76 | return; |
77 | add_vmfork_randomness(unique_vm_id: state->this_id, len: sizeof(state->this_id)); |
78 | } |
79 | |
80 | static const struct acpi_device_id vmgenid_ids[] = { |
81 | { "VMGENCTR" , 0 }, |
82 | { "VM_GEN_COUNTER" , 0 }, |
83 | { } |
84 | }; |
85 | |
86 | static 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 | |
96 | module_acpi_driver(vmgenid_driver); |
97 | |
98 | MODULE_DEVICE_TABLE(acpi, vmgenid_ids); |
99 | MODULE_DESCRIPTION("Virtual Machine Generation ID" ); |
100 | MODULE_LICENSE("GPL v2" ); |
101 | MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>" ); |
102 | |