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	char *envp[] = { "NEW_VMGENID=1", NULL };
 72	u8 old_id[VMGENID_SIZE];
 73
 74	memcpy(old_id, state->this_id, sizeof(old_id));
 75	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
 76	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
 77		return;
 78	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
 79	kobject_uevent_env(&device->dev.kobj, KOBJ_CHANGE, envp);
 80}
 81
 82static const struct acpi_device_id vmgenid_ids[] = {
 83	{ "VMGENCTR", 0 },
 84	{ "VM_GEN_COUNTER", 0 },
 85	{ }
 86};
 87
 88static struct acpi_driver vmgenid_driver = {
 89	.name = "vmgenid",
 90	.ids = vmgenid_ids,
 91	.owner = THIS_MODULE,
 92	.ops = {
 93		.add = vmgenid_add,
 94		.notify = vmgenid_notify
 95	}
 96};
 97
 98module_acpi_driver(vmgenid_driver);
 99
100MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
101MODULE_DESCRIPTION("Virtual Machine Generation ID");
102MODULE_LICENSE("GPL v2");
103MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");