// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 *
 * The "Virtual Machine Generation ID" is exposed via ACPI or DT and changes when a
 * virtual machine forks or is cloned. This driver exists for shepherding that
 * information to random.c.
 */

#include <linux/acpi.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/random.h>

ACPI_MODULE_NAME("vmgenid");

enum { VMGENID_SIZE = 16 };

struct vmgenid_state {
        u8 *next_id;
        u8 this_id[VMGENID_SIZE];
};

static void vmgenid_notify(struct device *device)
{
        struct vmgenid_state *state = device->driver_data;
        u8 old_id[VMGENID_SIZE];

        memcpy(old_id, state->this_id, sizeof(old_id));
        memcpy(state->this_id, state->next_id, sizeof(state->this_id));
        if (!memcmp(old_id, state->this_id, sizeof(old_id)))
                return;
        add_vmfork_randomness(state->this_id, sizeof(state->this_id));
}

static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
{
        state->next_id = virt_addr;
        memcpy(state->this_id, state->next_id, sizeof(state->this_id));
        add_device_randomness(state->this_id, sizeof(state->this_id));
}

#ifdef CONFIG_ACPI
static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
                                 u32 __always_unused event, void *dev)
{
        vmgenid_notify(dev);
}

static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
{
        struct acpi_device *device = ACPI_COMPANION(dev);
        struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
        union acpi_object *obj;
        phys_addr_t phys_addr;
        acpi_status status;
        void *virt_addr;
        int ret = 0;

        status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
        if (ACPI_FAILURE(status)) {
                ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
                return -ENODEV;
        }
        obj = parsed.pointer;
        if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 ||
            obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
            obj->package.elements[1].type != ACPI_TYPE_INTEGER) {
                ret = -EINVAL;
                goto out;
        }

        phys_addr = (obj->package.elements[0].integer.value << 0) |
                    (obj->package.elements[1].integer.value << 32);

        virt_addr = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
        if (IS_ERR(virt_addr)) {
                ret = PTR_ERR(virt_addr);
                goto out;
        }
        setup_vmgenid_state(state, virt_addr);

        status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
                                             vmgenid_acpi_handler, dev);
        if (ACPI_FAILURE(status)) {
                ret = -ENODEV;
                goto out;
        }

        dev->driver_data = state;
out:
        ACPI_FREE(parsed.pointer);
        return ret;
}
#else
static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
{
        return -EINVAL;
}
#endif

static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev)
{
        vmgenid_notify(dev);
        return IRQ_HANDLED;
}

static int vmgenid_add_of(struct platform_device *pdev,
                          struct vmgenid_state *state)
{
        void *virt_addr;
        int ret;

        virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
        if (IS_ERR(virt_addr))
                return PTR_ERR(virt_addr);

        setup_vmgenid_state(state, virt_addr);

        ret = platform_get_irq(pdev, 0);
        if (ret < 0)
                return ret;

        ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler,
                               IRQF_SHARED, "vmgenid", &pdev->dev);
        if (ret < 0)
                return ret;

        pdev->dev.driver_data = state;
        return 0;
}

static int vmgenid_add(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct vmgenid_state *state;
        int ret;

        state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL);
        if (!state)
                return -ENOMEM;

        if (dev->of_node)
                ret = vmgenid_add_of(pdev, state);
        else
                ret = vmgenid_add_acpi(dev, state);

        if (ret < 0)
                devm_kfree(dev, state);
        return ret;
}

static const struct of_device_id vmgenid_of_ids[] = {
        { .compatible = "microsoft,vmgenid", },
        { },
};
MODULE_DEVICE_TABLE(of, vmgenid_of_ids);

static const struct acpi_device_id vmgenid_acpi_ids[] = {
        { "VMGENCTR", 0 },
        { "VM_GEN_COUNTER", 0 },
        { }
};
MODULE_DEVICE_TABLE(acpi, vmgenid_acpi_ids);

static struct platform_driver vmgenid_plaform_driver = {
        .probe      = vmgenid_add,
        .driver     = {
                .name   = "vmgenid",
                .acpi_match_table = vmgenid_acpi_ids,
                .of_match_table = vmgenid_of_ids,
        },
};

module_platform_driver(vmgenid_plaform_driver)

MODULE_DESCRIPTION("Virtual Machine Generation ID");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Jason A. Donenfeld <Jason@zx2c4.com>");