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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*
* The "Virtual Machine Generation ID" is exposed via ACPI and changes when a
* virtual machine forks or is cloned. This driver exists for shepherding that
* information to random.c.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/acpi.h>
#include <linux/random.h>
ACPI_MODULE_NAME("vmgenid");
enum { VMGENID_SIZE = 16 };
struct vmgenid_state {
u8 *next_id;
u8 this_id[VMGENID_SIZE];
};
static int vmgenid_add(struct acpi_device *device)
{
struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
struct vmgenid_state *state;
union acpi_object *obj;
phys_addr_t phys_addr;
acpi_status status;
int ret = 0;
state = devm_kmalloc(&device->dev, sizeof(*state), GFP_KERNEL);
if (!state)
return -ENOMEM;
status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
if (ACPI_FAILURE(status)) {
ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
return -ENODEV;
}
obj = parsed.pointer;
if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 ||
obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
obj->package.elements[1].type != ACPI_TYPE_INTEGER) {
ret = -EINVAL;
goto out;
}
phys_addr = (obj->package.elements[0].integer.value << 0) |
(obj->package.elements[1].integer.value << 32);
state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
if (IS_ERR(state->next_id)) {
ret = PTR_ERR(state->next_id);
goto out;
}
memcpy(state->this_id, state->next_id, sizeof(state->this_id));
add_device_randomness(state->this_id, sizeof(state->this_id));
device->driver_data = state;
out:
ACPI_FREE(parsed.pointer);
return ret;
}
static void vmgenid_notify(struct acpi_device *device, u32 event)
{
struct vmgenid_state *state = acpi_driver_data(device);
char *envp[] = { "NEW_VMGENID=1", NULL };
u8 old_id[VMGENID_SIZE];
memcpy(old_id, state->this_id, sizeof(old_id));
memcpy(state->this_id, state->next_id, sizeof(state->this_id));
if (!memcmp(old_id, state->this_id, sizeof(old_id)))
return;
add_vmfork_randomness(state->this_id, sizeof(state->this_id));
kobject_uevent_env(&device->dev.kobj, KOBJ_CHANGE, envp);
}
static const struct acpi_device_id vmgenid_ids[] = {
{ "VMGENCTR", 0 },
{ "VM_GEN_COUNTER", 0 },
{ }
};
static struct acpi_driver vmgenid_driver = {
.name = "vmgenid",
.ids = vmgenid_ids,
.owner = THIS_MODULE,
.ops = {
.add = vmgenid_add,
.notify = vmgenid_notify
}
};
module_acpi_driver(vmgenid_driver);
MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
MODULE_DESCRIPTION("Virtual Machine Generation ID");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");
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