LXR linux/drivers/virt/vmgenid.c

   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