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 = dev_get_drvdata(device); 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, 79 MEMREMAP_WB | MEMREMAP_DEC); 80 if (IS_ERR(virt_addr)) { 81 ret = PTR_ERR(virt_addr); 82 goto out; 83 } 84 setup_vmgenid_state(state, virt_addr); 85 86 dev_set_drvdata(dev, state); 87 88 status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY, 89 vmgenid_acpi_handler, dev); 90 if (ACPI_FAILURE(status)) { 91 ret = -ENODEV; 92 goto out; 93 } 94 95 out: 96 ACPI_FREE(parsed.pointer); 97 return ret; 98 } 99 #else 100 static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state) 101 { 102 return -EINVAL; 103 } 104 #endif 105 106 static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev) 107 { 108 vmgenid_notify(dev); 109 return IRQ_HANDLED; 110 } 111 112 static int vmgenid_add_of(struct platform_device *pdev, 113 struct vmgenid_state *state) 114 { 115 void *virt_addr; 116 int ret; 117 118 virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL); 119 if (IS_ERR(virt_addr)) 120 return PTR_ERR(virt_addr); 121 122 setup_vmgenid_state(state, virt_addr); 123 124 ret = platform_get_irq(pdev, 0); 125 if (ret < 0) 126 return ret; 127 128 dev_set_drvdata(&pdev->dev, state); 129 130 ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler, 131 IRQF_SHARED, "vmgenid", &pdev->dev); 132 if (ret < 0) 133 return ret; 134 135 return 0; 136 } 137 138 static int vmgenid_add(struct platform_device *pdev) 139 { 140 struct device *dev = &pdev->dev; 141 struct vmgenid_state *state; 142 int ret; 143 144 state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL); 145 if (!state) 146 return -ENOMEM; 147 148 if (dev->of_node) 149 ret = vmgenid_add_of(pdev, state); 150 else 151 ret = vmgenid_add_acpi(dev, state); 152 153 if (ret < 0) 154 devm_kfree(dev, state); 155 return ret; 156 } 157 158 static const struct of_device_id vmgenid_of_ids[] = { 159 { .compatible = "microsoft,vmgenid", }, 160 { }, 161 }; 162 MODULE_DEVICE_TABLE(of, vmgenid_of_ids); 163 164 static const struct acpi_device_id vmgenid_acpi_ids[] = { 165 { "VMGENCTR", 0 }, 166 { "VM_GEN_COUNTER", 0 }, 167 { } 168 }; 169 MODULE_DEVICE_TABLE(acpi, vmgenid_acpi_ids); 170 171 static struct platform_driver vmgenid_plaform_driver = { 172 .probe = vmgenid_add, 173 .driver = { 174 .name = "vmgenid", 175 .acpi_match_table = vmgenid_acpi_ids, 176 .of_match_table = vmgenid_of_ids, 177 }, 178 }; 179 180 module_platform_driver(vmgenid_plaform_driver) 181 182 MODULE_DESCRIPTION("Virtual Machine Generation ID"); 183 MODULE_LICENSE("GPL v2"); 184 MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>"); 185