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 15 ACPI_MODULE_NAME("vmgenid"); 16 17 enum { VMGENID_SIZE = 16 }; 18 19 struct vmgenid_state { 20 u8 *next_id; 21 u8 this_id[VMGENID_SIZE]; 22 }; 23 24 static 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 63 out: 64 ACPI_FREE(parsed.pointer); 65 return ret; 66 } 67 68 static 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 80 static const struct acpi_device_id vmgenid_ids[] = { 81 { "VMGENCTR", 0 }, 82 { "VM_GEN_COUNTER", 0 }, 83 { } 84 }; 85 86 static 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 96 module_acpi_driver(vmgenid_driver); 97 98 MODULE_DEVICE_TABLE(acpi, vmgenid_ids); 99 MODULE_DESCRIPTION("Virtual Machine Generation ID"); 100 MODULE_LICENSE("GPL v2"); 101 MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>"); 102