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 or DT 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/acpi.h>
  11 #include <linux/interrupt.h>
  12 #include <linux/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/platform_device.h>
  15 #include <linux/random.h>
  16
  17 ACPI_MODULE_NAME("vmgenid");
  18
  19 enum { VMGENID_SIZE = 16 };
  20
  21 struct vmgenid_state {
  22         u8 *next_id;
  23         u8 this_id[VMGENID_SIZE];
  24 };
  25
  26 static void vmgenid_notify(struct device *device)
  27 {
  28         struct vmgenid_state *state = device->driver_data;
  29         u8 old_id[VMGENID_SIZE];
  30
  31         memcpy(old_id, state->this_id, sizeof(old_id));
  32         memcpy(state->this_id, state->next_id, sizeof(state->this_id));
  33         if (!memcmp(old_id, state->this_id, sizeof(old_id)))
  34                 return;
  35         add_vmfork_randomness(state->this_id, sizeof(state->this_id));
  36 }
  37
  38 static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
  39 {
  40         state->next_id = virt_addr;
  41         memcpy(state->this_id, state->next_id, sizeof(state->this_id));
  42         add_device_randomness(state->this_id, sizeof(state->this_id));
  43 }
  44
  45 #ifdef CONFIG_ACPI
  46 static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
  47                                  u32 __always_unused event, void *dev)
  48 {
  49         vmgenid_notify(dev);
  50 }
  51
  52 static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
  53 {
  54         struct acpi_device *device = ACPI_COMPANION(dev);
  55         struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
  56         union acpi_object *obj;
  57         phys_addr_t phys_addr;
  58         acpi_status status;
  59         void *virt_addr;
  60         int ret = 0;
  61
  62         status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
  63         if (ACPI_FAILURE(status)) {
  64                 ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
  65                 return -ENODEV;
  66         }
  67         obj = parsed.pointer;
  68         if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 ||
  69             obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
  70             obj->package.elements[1].type != ACPI_TYPE_INTEGER) {
  71                 ret = -EINVAL;
  72                 goto out;
  73         }
  74
  75         phys_addr = (obj->package.elements[0].integer.value << 0) |
  76                     (obj->package.elements[1].integer.value << 32);
  77
  78         virt_addr = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
  79         if (IS_ERR(virt_addr)) {
  80                 ret = PTR_ERR(virt_addr);
  81                 goto out;
  82         }
  83         setup_vmgenid_state(state, virt_addr);
  84
  85         status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
  86                                              vmgenid_acpi_handler, dev);
  87         if (ACPI_FAILURE(status)) {
  88                 ret = -ENODEV;
  89                 goto out;
  90         }
  91
  92         dev->driver_data = state;
  93 out:
  94         ACPI_FREE(parsed.pointer);
  95         return ret;
  96 }
  97 #else
  98 static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
  99 {
 100         return -EINVAL;
 101 }
 102 #endif
 103
 104 static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev)
 105 {
 106         vmgenid_notify(dev);
 107         return IRQ_HANDLED;
 108 }
 109
 110 static int vmgenid_add_of(struct platform_device *pdev,
 111                           struct vmgenid_state *state)
 112 {
 113         void *virt_addr;
 114         int ret;
 115
 116         virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
 117         if (IS_ERR(virt_addr))
 118                 return PTR_ERR(virt_addr);
 119
 120         setup_vmgenid_state(state, virt_addr);
 121
 122         ret = platform_get_irq(pdev, 0);
 123         if (ret < 0)
 124                 return ret;
 125
 126         ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler,
 127                                IRQF_SHARED, "vmgenid", &pdev->dev);
 128         if (ret < 0)
 129                 return ret;
 130
 131         pdev->dev.driver_data = state;
 132         return 0;
 133 }
 134
 135 static int vmgenid_add(struct platform_device *pdev)
 136 {
 137         struct device *dev = &pdev->dev;
 138         struct vmgenid_state *state;
 139         int ret;
 140
 141         state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL);
 142         if (!state)
 143                 return -ENOMEM;
 144
 145         if (dev->of_node)
 146                 ret = vmgenid_add_of(pdev, state);
 147         else
 148                 ret = vmgenid_add_acpi(dev, state);
 149
 150         if (ret < 0)
 151                 devm_kfree(dev, state);
 152         return ret;
 153 }
 154
 155 static const struct of_device_id vmgenid_of_ids[] = {
 156         { .compatible = "microsoft,vmgenid", },
 157         { },
 158 };
 159 MODULE_DEVICE_TABLE(of, vmgenid_of_ids);
 160
 161 static const struct acpi_device_id vmgenid_acpi_ids[] = {
 162         { "VMGENCTR", 0 },
 163         { "VM_GEN_COUNTER", 0 },
 164         { }
 165 };
 166 MODULE_DEVICE_TABLE(acpi, vmgenid_acpi_ids);
 167
 168 static struct platform_driver vmgenid_plaform_driver = {
 169         .probe      = vmgenid_add,
 170         .driver     = {
 171                 .name   = "vmgenid",
 172                 .acpi_match_table = vmgenid_acpi_ids,
 173                 .of_match_table = vmgenid_of_ids,
 174         },
 175 };
 176
 177 module_platform_driver(vmgenid_plaform_driver)
 178
 179 MODULE_DESCRIPTION("Virtual Machine Generation ID");
 180 MODULE_LICENSE("GPL v2");
 181 MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");