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>"); 182