/*
 * hw_random/core.c: HWRNG core API
 *
 * Copyright 2006 Michael Buesch <m@bues.ch>
 * Copyright 2005 (c) MontaVista Software, Inc.
 *
 * Please read Documentation/admin-guide/hw_random.rst for details on use.
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */

#include <linux/delay.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/fs.h>
#include <linux/hw_random.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/sched/signal.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

#define RNG_MODULE_NAME         "hw_random"

static struct hwrng *current_rng;
/* the current rng has been explicitly chosen by user via sysfs */
static int cur_rng_set_by_user;
static struct task_struct *hwrng_fill;
/* list of registered rngs, sorted decending by quality */
static LIST_HEAD(rng_list);
/* Protects rng_list and current_rng */
static DEFINE_MUTEX(rng_mutex);
/* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
static DEFINE_MUTEX(reading_mutex);
static int data_avail;
static u8 *rng_buffer, *rng_fillbuf;
static unsigned short current_quality;
static unsigned short default_quality; /* = 0; default to "off" */

module_param(current_quality, ushort, 0644);
MODULE_PARM_DESC(current_quality,
                 "current hwrng entropy estimation per 1024 bits of input");
module_param(default_quality, ushort, 0644);
MODULE_PARM_DESC(default_quality,
                 "default entropy content of hwrng per 1024 bits of input");

static void drop_current_rng(void);
static int hwrng_init(struct hwrng *rng);
static void start_khwrngd(void);

static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
                               int wait);

static size_t rng_buffer_size(void)
{
        return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
}

static void add_early_randomness(struct hwrng *rng)
{
        int bytes_read;
        size_t size = min_t(size_t, 16, rng_buffer_size());

        mutex_lock(&reading_mutex);
        bytes_read = rng_get_data(rng, rng_buffer, size, 1);
        mutex_unlock(&reading_mutex);
        if (bytes_read > 0)
                add_device_randomness(rng_buffer, bytes_read);
}

static inline void cleanup_rng(struct kref *kref)
{
        struct hwrng *rng = container_of(kref, struct hwrng, ref);

        if (rng->cleanup)
                rng->cleanup(rng);

        complete(&rng->cleanup_done);
}

static int set_current_rng(struct hwrng *rng)
{
        int err;

        BUG_ON(!mutex_is_locked(&rng_mutex));

        err = hwrng_init(rng);
        if (err)
                return err;

        drop_current_rng();
        current_rng = rng;

        return 0;
}

static void drop_current_rng(void)
{
        BUG_ON(!mutex_is_locked(&rng_mutex));
        if (!current_rng)
                return;

        /* decrease last reference for triggering the cleanup */
        kref_put(&current_rng->ref, cleanup_rng);
        current_rng = NULL;
}

/* Returns ERR_PTR(), NULL or refcounted hwrng */
static struct hwrng *get_current_rng(void)
{
        struct hwrng *rng;

        if (mutex_lock_interruptible(&rng_mutex))
                return ERR_PTR(-ERESTARTSYS);

        rng = current_rng;
        if (rng)
                kref_get(&rng->ref);

        mutex_unlock(&rng_mutex);
        return rng;
}

static void put_rng(struct hwrng *rng)
{
        /*
         * Hold rng_mutex here so we serialize in case they set_current_rng
         * on rng again immediately.
         */
        mutex_lock(&rng_mutex);
        if (rng)
                kref_put(&rng->ref, cleanup_rng);
        mutex_unlock(&rng_mutex);
}

static int hwrng_init(struct hwrng *rng)
{
        if (kref_get_unless_zero(&rng->ref))
                goto skip_init;

        if (rng->init) {
                int ret;

                ret =  rng->init(rng);
                if (ret)
                        return ret;
        }

        kref_init(&rng->ref);
        reinit_completion(&rng->cleanup_done);

skip_init:
        add_early_randomness(rng);

        current_quality = rng->quality ? : default_quality;
        if (current_quality > 1024)
                current_quality = 1024;

        if (current_quality == 0 && hwrng_fill)
                kthread_stop(hwrng_fill);
        if (current_quality > 0 && !hwrng_fill)
                start_khwrngd();

        return 0;
}

static int rng_dev_open(struct inode *inode, struct file *filp)
{
        /* enforce read-only access to this chrdev */
        if ((filp->f_mode & FMODE_READ) == 0)
                return -EINVAL;
        if (filp->f_mode & FMODE_WRITE)
                return -EINVAL;
        return 0;
}

static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
                        int wait) {
        int present;

        BUG_ON(!mutex_is_locked(&reading_mutex));
        if (rng->read)
                return rng->read(rng, (void *)buffer, size, wait);

        if (rng->data_present)
                present = rng->data_present(rng, wait);
        else
                present = 1;

        if (present)
                return rng->data_read(rng, (u32 *)buffer);

        return 0;
}

static ssize_t rng_dev_read(struct file *filp, char __user *buf,
                            size_t size, loff_t *offp)
{
        ssize_t ret = 0;
        int err = 0;
        int bytes_read, len;
        struct hwrng *rng;

        while (size) {
                rng = get_current_rng();
                if (IS_ERR(rng)) {
                        err = PTR_ERR(rng);
                        goto out;
                }
                if (!rng) {
                        err = -ENODEV;
                        goto out;
                }

                if (mutex_lock_interruptible(&reading_mutex)) {
                        err = -ERESTARTSYS;
                        goto out_put;
                }
                if (!data_avail) {
                        bytes_read = rng_get_data(rng, rng_buffer,
                                rng_buffer_size(),
                                !(filp->f_flags & O_NONBLOCK));
                        if (bytes_read < 0) {
                                err = bytes_read;
                                goto out_unlock_reading;
                        }
                        data_avail = bytes_read;
                }

                if (!data_avail) {
                        if (filp->f_flags & O_NONBLOCK) {
                                err = -EAGAIN;
                                goto out_unlock_reading;
                        }
                } else {
                        len = data_avail;
                        if (len > size)
                                len = size;

                        data_avail -= len;

                        if (copy_to_user(buf + ret, rng_buffer + data_avail,
                                                                len)) {
                                err = -EFAULT;
                                goto out_unlock_reading;
                        }

                        size -= len;
                        ret += len;
                }

                mutex_unlock(&reading_mutex);
                put_rng(rng);

                if (need_resched())
                        schedule_timeout_interruptible(1);

                if (signal_pending(current)) {
                        err = -ERESTARTSYS;
                        goto out;
                }
        }
out:
        return ret ? : err;

out_unlock_reading:
        mutex_unlock(&reading_mutex);
out_put:
        put_rng(rng);
        goto out;
}

static const struct file_operations rng_chrdev_ops = {
        .owner          = THIS_MODULE,
        .open           = rng_dev_open,
        .read           = rng_dev_read,
        .llseek         = noop_llseek,
};

static const struct attribute_group *rng_dev_groups[];

static struct miscdevice rng_miscdev = {
        .minor          = HWRNG_MINOR,
        .name           = RNG_MODULE_NAME,
        .nodename       = "hwrng",
        .fops           = &rng_chrdev_ops,
        .groups         = rng_dev_groups,
};

static int enable_best_rng(void)
{
        int ret = -ENODEV;

        BUG_ON(!mutex_is_locked(&rng_mutex));

        /* rng_list is sorted by quality, use the best (=first) one */
        if (!list_empty(&rng_list)) {
                struct hwrng *new_rng;

                new_rng = list_entry(rng_list.next, struct hwrng, list);
                ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
                if (!ret)
                        cur_rng_set_by_user = 0;
        } else {
                drop_current_rng();
                cur_rng_set_by_user = 0;
                ret = 0;
        }

        return ret;
}

static ssize_t hwrng_attr_current_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t len)
{
        int err = -ENODEV;
        struct hwrng *rng;

        err = mutex_lock_interruptible(&rng_mutex);
        if (err)
                return -ERESTARTSYS;

        if (sysfs_streq(buf, "")) {
                err = enable_best_rng();
        } else {
                list_for_each_entry(rng, &rng_list, list) {
                        if (sysfs_streq(rng->name, buf)) {
                                cur_rng_set_by_user = 1;
                                err = set_current_rng(rng);
                                break;
                        }
                }
        }

        mutex_unlock(&rng_mutex);

        return err ? : len;
}

static ssize_t hwrng_attr_current_show(struct device *dev,
                                       struct device_attribute *attr,
                                       char *buf)
{
        ssize_t ret;
        struct hwrng *rng;

        rng = get_current_rng();
        if (IS_ERR(rng))
                return PTR_ERR(rng);

        ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
        put_rng(rng);

        return ret;
}

static ssize_t hwrng_attr_available_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
{
        int err;
        struct hwrng *rng;

        err = mutex_lock_interruptible(&rng_mutex);
        if (err)
                return -ERESTARTSYS;
        buf[0] = '\0';
        list_for_each_entry(rng, &rng_list, list) {
                strlcat(buf, rng->name, PAGE_SIZE);
                strlcat(buf, " ", PAGE_SIZE);
        }
        strlcat(buf, "\n", PAGE_SIZE);
        mutex_unlock(&rng_mutex);

        return strlen(buf);
}

static ssize_t hwrng_attr_selected_show(struct device *dev,
                                        struct device_attribute *attr,
                                        char *buf)
{
        return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
}

static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
                   hwrng_attr_current_show,
                   hwrng_attr_current_store);
static DEVICE_ATTR(rng_available, S_IRUGO,
                   hwrng_attr_available_show,
                   NULL);
static DEVICE_ATTR(rng_selected, S_IRUGO,
                   hwrng_attr_selected_show,
                   NULL);

static struct attribute *rng_dev_attrs[] = {
        &dev_attr_rng_current.attr,
        &dev_attr_rng_available.attr,
        &dev_attr_rng_selected.attr,
        NULL
};

ATTRIBUTE_GROUPS(rng_dev);

static void __exit unregister_miscdev(void)
{
        misc_deregister(&rng_miscdev);
}

static int __init register_miscdev(void)
{
        return misc_register(&rng_miscdev);
}

static int hwrng_fillfn(void *unused)
{
        long rc;

        while (!kthread_should_stop()) {
                struct hwrng *rng;

                rng = get_current_rng();
                if (IS_ERR(rng) || !rng)
                        break;
                mutex_lock(&reading_mutex);
                rc = rng_get_data(rng, rng_fillbuf,
                                  rng_buffer_size(), 1);
                mutex_unlock(&reading_mutex);
                put_rng(rng);
                if (rc <= 0) {
                        pr_warn("hwrng: no data available\n");
                        msleep_interruptible(10000);
                        continue;
                }
                /* Outside lock, sure, but y'know: randomness. */
                add_hwgenerator_randomness((void *)rng_fillbuf, rc,
                                           rc * current_quality * 8 >> 10);
        }
        hwrng_fill = NULL;
        return 0;
}

static void start_khwrngd(void)
{
        hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
        if (IS_ERR(hwrng_fill)) {
                pr_err("hwrng_fill thread creation failed\n");
                hwrng_fill = NULL;
        }
}

int hwrng_register(struct hwrng *rng)
{
        int err = -EINVAL;
        struct hwrng *old_rng, *tmp;
        struct list_head *rng_list_ptr;

        if (!rng->name || (!rng->data_read && !rng->read))
                goto out;

        mutex_lock(&rng_mutex);
        /* Must not register two RNGs with the same name. */
        err = -EEXIST;
        list_for_each_entry(tmp, &rng_list, list) {
                if (strcmp(tmp->name, rng->name) == 0)
                        goto out_unlock;
        }

        init_completion(&rng->cleanup_done);
        complete(&rng->cleanup_done);

        /* rng_list is sorted by decreasing quality */
        list_for_each(rng_list_ptr, &rng_list) {
                tmp = list_entry(rng_list_ptr, struct hwrng, list);
                if (tmp->quality < rng->quality)
                        break;
        }
        list_add_tail(&rng->list, rng_list_ptr);

        old_rng = current_rng;
        err = 0;
        if (!old_rng ||
            (!cur_rng_set_by_user && rng->quality > old_rng->quality)) {
                /*
                 * Set new rng as current as the new rng source
                 * provides better entropy quality and was not
                 * chosen by userspace.
                 */
                err = set_current_rng(rng);
                if (err)
                        goto out_unlock;
        }

        if (old_rng && !rng->init) {
                /*
                 * Use a new device's input to add some randomness to
                 * the system.  If this rng device isn't going to be
                 * used right away, its init function hasn't been
                 * called yet; so only use the randomness from devices
                 * that don't need an init callback.
                 */
                add_early_randomness(rng);
        }

out_unlock:
        mutex_unlock(&rng_mutex);
out:
        return err;
}
EXPORT_SYMBOL_GPL(hwrng_register);

void hwrng_unregister(struct hwrng *rng)
{
        int err;

        mutex_lock(&rng_mutex);

        list_del(&rng->list);
        if (current_rng == rng) {
                err = enable_best_rng();
                if (err) {
                        drop_current_rng();
                        cur_rng_set_by_user = 0;
                }
        }

        if (list_empty(&rng_list)) {
                mutex_unlock(&rng_mutex);
                if (hwrng_fill)
                        kthread_stop(hwrng_fill);
        } else
                mutex_unlock(&rng_mutex);

        wait_for_completion(&rng->cleanup_done);
}
EXPORT_SYMBOL_GPL(hwrng_unregister);

static void devm_hwrng_release(struct device *dev, void *res)
{
        hwrng_unregister(*(struct hwrng **)res);
}

static int devm_hwrng_match(struct device *dev, void *res, void *data)
{
        struct hwrng **r = res;

        if (WARN_ON(!r || !*r))
                return 0;

        return *r == data;
}

int devm_hwrng_register(struct device *dev, struct hwrng *rng)
{
        struct hwrng **ptr;
        int error;

        ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return -ENOMEM;

        error = hwrng_register(rng);
        if (error) {
                devres_free(ptr);
                return error;
        }

        *ptr = rng;
        devres_add(dev, ptr);
        return 0;
}
EXPORT_SYMBOL_GPL(devm_hwrng_register);

void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
{
        devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
}
EXPORT_SYMBOL_GPL(devm_hwrng_unregister);

static int __init hwrng_modinit(void)
{
        int ret = -ENOMEM;

        /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
        rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
        if (!rng_buffer)
                return -ENOMEM;

        rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
        if (!rng_fillbuf) {
                kfree(rng_buffer);
                return -ENOMEM;
        }

        ret = register_miscdev();
        if (ret) {
                kfree(rng_fillbuf);
                kfree(rng_buffer);
        }

        return ret;
}

static void __exit hwrng_modexit(void)
{
        mutex_lock(&rng_mutex);
        BUG_ON(current_rng);
        kfree(rng_buffer);
        kfree(rng_fillbuf);
        mutex_unlock(&rng_mutex);

        unregister_miscdev();
}

module_init(hwrng_modinit);
module_exit(hwrng_modexit);

MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
MODULE_LICENSE("GPL");