// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2021 - Google LLC
 * Author: David Brazdil <dbrazdil@google.com>
 *
 * Driver for Open Profile for DICE.
 *
 * This driver takes ownership of a reserved memory region containing data
 * generated by the Open Profile for DICE measured boot protocol. The memory
 * contents are not interpreted by the kernel but can be mapped into a userspace
 * process via a misc device. Userspace can also request a wipe of the memory.
 *
 * Userspace can access the data with (w/o error handling):
 *
 *     fd = open("/dev/open-dice0", O_RDWR);
 *     read(fd, &size, sizeof(unsigned long));
 *     data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
 *     write(fd, NULL, 0); // wipe
 *     close(fd);
 */

#include <linux/io.h>
#include <linux/miscdevice.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/of_reserved_mem.h>
#include <linux/platform_device.h>

#define DRIVER_NAME "open-dice"

struct open_dice_drvdata {
        struct mutex lock;
        char name[16];
        struct reserved_mem *rmem;
        struct miscdevice misc;
};

static inline struct open_dice_drvdata *to_open_dice_drvdata(struct file *filp)
{
        return container_of(filp->private_data, struct open_dice_drvdata, misc);
}

static int open_dice_wipe(struct open_dice_drvdata *drvdata)
{
        void *kaddr;

        mutex_lock(&drvdata->lock);
        kaddr = devm_memremap(drvdata->misc.this_device, drvdata->rmem->base,
                              drvdata->rmem->size, MEMREMAP_WC);
        if (IS_ERR(kaddr)) {
                mutex_unlock(&drvdata->lock);
                return PTR_ERR(kaddr);
        }

        memset(kaddr, 0, drvdata->rmem->size);
        devm_memunmap(drvdata->misc.this_device, kaddr);
        mutex_unlock(&drvdata->lock);
        return 0;
}

/*
 * Copies the size of the reserved memory region to the user-provided buffer.
 */
static ssize_t open_dice_read(struct file *filp, char __user *ptr, size_t len,
                              loff_t *off)
{
        unsigned long val = to_open_dice_drvdata(filp)->rmem->size;

        return simple_read_from_buffer(ptr, len, off, &val, sizeof(val));
}

/*
 * Triggers a wipe of the reserved memory region. The user-provided pointer
 * is never dereferenced.
 */
static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
                               size_t len, loff_t *off)
{
        if (open_dice_wipe(to_open_dice_drvdata(filp)))
                return -EIO;

        /* Consume the input buffer. */
        return len;
}

/*
 * Creates a mapping of the reserved memory region in user address space.
 */
static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
{
        struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);

        if (vma->vm_flags & VM_MAYSHARE) {
                /* Do not allow userspace to modify the underlying data. */
                if (vma->vm_flags & VM_WRITE)
                        return -EPERM;
                /* Ensure userspace cannot acquire VM_WRITE later. */
                vm_flags_clear(vma, VM_MAYWRITE);
        }

        /* Create write-combine mapping so all clients observe a wipe. */
        vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
        vm_flags_set(vma, VM_DONTCOPY | VM_DONTDUMP);
        return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size);
}

static const struct file_operations open_dice_fops = {
        .owner = THIS_MODULE,
        .read = open_dice_read,
        .write = open_dice_write,
        .mmap = open_dice_mmap,
};

static int __init open_dice_probe(struct platform_device *pdev)
{
        static unsigned int dev_idx;
        struct device *dev = &pdev->dev;
        struct reserved_mem *rmem;
        struct open_dice_drvdata *drvdata;
        int ret;

        rmem = of_reserved_mem_lookup(dev->of_node);
        if (!rmem) {
                dev_err(dev, "failed to lookup reserved memory\n");
                return -EINVAL;
        }

        if (!rmem->size || (rmem->size > ULONG_MAX)) {
                dev_err(dev, "invalid memory region size\n");
                return -EINVAL;
        }

        if (!PAGE_ALIGNED(rmem->base) || !PAGE_ALIGNED(rmem->size)) {
                dev_err(dev, "memory region must be page-aligned\n");
                return -EINVAL;
        }

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

        *drvdata = (struct open_dice_drvdata){
                .rmem = rmem,
                .misc = (struct miscdevice){
                        .parent = dev,
                        .name   = drvdata->name,
                        .minor  = MISC_DYNAMIC_MINOR,
                        .fops   = &open_dice_fops,
                        .mode   = 0600,
                },
        };
        mutex_init(&drvdata->lock);

        /* Index overflow check not needed, misc_register() will fail. */
        snprintf(drvdata->name, sizeof(drvdata->name), DRIVER_NAME"%u", dev_idx++);

        ret = misc_register(&drvdata->misc);
        if (ret) {
                dev_err(dev, "failed to register misc device '%s': %d\n",
                        drvdata->name, ret);
                return ret;
        }

        platform_set_drvdata(pdev, drvdata);
        return 0;
}

static void open_dice_remove(struct platform_device *pdev)
{
        struct open_dice_drvdata *drvdata = platform_get_drvdata(pdev);

        misc_deregister(&drvdata->misc);
}

static const struct of_device_id open_dice_of_match[] = {
        { .compatible = "google,open-dice" },
        {},
};

static struct platform_driver open_dice_driver = {
        .remove = open_dice_remove,
        .driver = {
                .name = DRIVER_NAME,
                .of_match_table = open_dice_of_match,
        },
};

static int __init open_dice_init(void)
{
        int ret = platform_driver_probe(&open_dice_driver, open_dice_probe);

        /* DICE regions are optional. Succeed even with zero instances. */
        return (ret == -ENODEV) ? 0 : ret;
}

static void __exit open_dice_exit(void)
{
        platform_driver_unregister(&open_dice_driver);
}

module_init(open_dice_init);
module_exit(open_dice_exit);

MODULE_DESCRIPTION("Driver for Open Profile for DICE.");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("David Brazdil <dbrazdil@google.com>");