blob: a3bbdd6e60fca2a75e48e2fa2cac86e329ae784c [file] [log] [blame]
/*
* 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/miscdevice.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/uaccess.h>
#define RNG_MODULE_NAME "hw_random"
#define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES)
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 */
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 = 1024; /* default to maximum */
module_param(current_quality, ushort, 0644);
MODULE_PARM_DESC(current_quality,
"current hwrng entropy estimation per 1024 bits of input -- obsolete, use rng_quality instead");
module_param(default_quality, ushort, 0644);
MODULE_PARM_DESC(default_quality,
"default maximum entropy content of hwrng per 1024 bits of input");
static void drop_current_rng(void);
static int hwrng_init(struct hwrng *rng);
static int hwrng_fillfn(void *unused);
static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
int wait);
static size_t rng_buffer_size(void)
{
return RNG_BUFFER_SIZE;
}
static void add_early_randomness(struct hwrng *rng)
{
int bytes_read;
mutex_lock(&reading_mutex);
bytes_read = rng_get_data(rng, rng_fillbuf, 32, 0);
mutex_unlock(&reading_mutex);
if (bytes_read > 0) {
size_t entropy = bytes_read * 8 * rng->quality / 1024;
add_hwgenerator_randomness(rng_fillbuf, bytes_read, entropy, false);
}
}
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;
/* if necessary, start hwrng thread */
if (!hwrng_fill) {
hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
if (IS_ERR(hwrng_fill)) {
pr_err("hwrng_fill thread creation failed\n");
hwrng_fill = NULL;
}
}
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_nolock(void)
{
if (current_rng)
kref_get(&current_rng->ref);
return current_rng;
}
static struct hwrng *get_current_rng(void)
{
struct hwrng *rng;
if (mutex_lock_interruptible(&rng_mutex))
return ERR_PTR(-ERESTARTSYS);
rng = get_current_rng_nolock();
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:
rng->quality = min_t(u16, min_t(u16, default_quality, 1024), rng->quality ?: 1024);
current_quality = rng->quality; /* obsolete */
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)
{
u8 buffer[RNG_BUFFER_SIZE];
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;
} else if (bytes_read == 0 &&
(filp->f_flags & O_NONBLOCK)) {
err = -EAGAIN;
goto out_unlock_reading;
}
data_avail = bytes_read;
}
len = data_avail;
if (len) {
if (len > size)
len = size;
data_avail -= len;
memcpy(buffer, rng_buffer + data_avail, len);
}
mutex_unlock(&reading_mutex);
put_rng(rng);
if (len) {
if (copy_to_user(buf + ret, buffer, len)) {
err = -EFAULT;
goto out;
}
size -= len;
ret += len;
}
if (need_resched())
schedule_timeout_interruptible(1);
if (signal_pending(current)) {
err = -ERESTARTSYS;
goto out;
}
}
out:
memzero_explicit(buffer, sizeof(buffer));
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)
{
struct hwrng *rng, *new_rng = NULL;
int ret = -ENODEV;
BUG_ON(!mutex_is_locked(&rng_mutex));
/* no rng to use? */
if (list_empty(&rng_list)) {
drop_current_rng();
cur_rng_set_by_user = 0;
return 0;
}
/* use the rng which offers the best quality */
list_for_each_entry(rng, &rng_list, list) {
if (!new_rng || rng->quality > new_rng->quality)
new_rng = rng;
}
ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
if (!ret)
cur_rng_set_by_user = 0;
return ret;
}
static ssize_t rng_current_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t len)
{
int err;
struct hwrng *rng, *old_rng, *new_rng;
err = mutex_lock_interruptible(&rng_mutex);
if (err)
return -ERESTARTSYS;
old_rng = current_rng;
if (sysfs_streq(buf, "")) {
err = enable_best_rng();
} else {
list_for_each_entry(rng, &rng_list, list) {
if (sysfs_streq(rng->name, buf)) {
err = set_current_rng(rng);
if (!err)
cur_rng_set_by_user = 1;
break;
}
}
}
new_rng = get_current_rng_nolock();
mutex_unlock(&rng_mutex);
if (new_rng) {
if (new_rng != old_rng)
add_early_randomness(new_rng);
put_rng(new_rng);
}
return err ? : len;
}
static ssize_t rng_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 rng_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 rng_selected_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%d\n", cur_rng_set_by_user);
}
static ssize_t rng_quality_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);
if (!rng) /* no need to put_rng */
return -ENODEV;
ret = sysfs_emit(buf, "%hu\n", rng->quality);
put_rng(rng);
return ret;
}
static ssize_t rng_quality_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t len)
{
u16 quality;
int ret = -EINVAL;
if (len < 2)
return -EINVAL;
ret = mutex_lock_interruptible(&rng_mutex);
if (ret)
return -ERESTARTSYS;
ret = kstrtou16(buf, 0, &quality);
if (ret || quality > 1024) {
ret = -EINVAL;
goto out;
}
if (!current_rng) {
ret = -ENODEV;
goto out;
}
current_rng->quality = quality;
current_quality = quality; /* obsolete */
/* the best available RNG may have changed */
ret = enable_best_rng();
out:
mutex_unlock(&rng_mutex);
return ret ? ret : len;
}
static DEVICE_ATTR_RW(rng_current);
static DEVICE_ATTR_RO(rng_available);
static DEVICE_ATTR_RO(rng_selected);
static DEVICE_ATTR_RW(rng_quality);
static struct attribute *rng_dev_attrs[] = {
&dev_attr_rng_current.attr,
&dev_attr_rng_available.attr,
&dev_attr_rng_selected.attr,
&dev_attr_rng_quality.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)
{
size_t entropy, entropy_credit = 0; /* in 1/1024 of a bit */
long rc;
while (!kthread_should_stop()) {
unsigned short quality;
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);
if (current_quality != rng->quality)
rng->quality = current_quality; /* obsolete */
quality = rng->quality;
mutex_unlock(&reading_mutex);
if (rc <= 0)
hwrng_msleep(rng, 10000);
put_rng(rng);
if (rc <= 0)
continue;
/* If we cannot credit at least one bit of entropy,
* keep track of the remainder for the next iteration
*/
entropy = rc * quality * 8 + entropy_credit;
if ((entropy >> 10) == 0)
entropy_credit = entropy;
/* Outside lock, sure, but y'know: randomness. */
add_hwgenerator_randomness((void *)rng_fillbuf, rc,
entropy >> 10, true);
}
hwrng_fill = NULL;
return 0;
}
int hwrng_register(struct hwrng *rng)
{
int err = -EINVAL;
struct hwrng *tmp;
bool is_new_current = false;
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;
}
list_add_tail(&rng->list, &rng_list);
init_completion(&rng->cleanup_done);
complete(&rng->cleanup_done);
init_completion(&rng->dying);
if (!current_rng ||
(!cur_rng_set_by_user && rng->quality > current_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;
/* to use current_rng in add_early_randomness() we need
* to take a ref
*/
is_new_current = true;
kref_get(&rng->ref);
}
mutex_unlock(&rng_mutex);
if (is_new_current || !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 by set_current_rng(); so only use the
* randomness from devices that don't need an init callback
*/
add_early_randomness(rng);
}
if (is_new_current)
put_rng(rng);
return 0;
out_unlock:
mutex_unlock(&rng_mutex);
out:
return err;
}
EXPORT_SYMBOL_GPL(hwrng_register);
void hwrng_unregister(struct hwrng *rng)
{
struct hwrng *old_rng, *new_rng;
int err;
mutex_lock(&rng_mutex);
old_rng = current_rng;
list_del(&rng->list);
complete_all(&rng->dying);
if (current_rng == rng) {
err = enable_best_rng();
if (err) {
drop_current_rng();
cur_rng_set_by_user = 0;
}
}
new_rng = get_current_rng_nolock();
if (list_empty(&rng_list)) {
mutex_unlock(&rng_mutex);
if (hwrng_fill)
kthread_stop(hwrng_fill);
} else
mutex_unlock(&rng_mutex);
if (new_rng) {
if (old_rng != new_rng)
add_early_randomness(new_rng);
put_rng(new_rng);
}
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);
long hwrng_msleep(struct hwrng *rng, unsigned int msecs)
{
unsigned long timeout = msecs_to_jiffies(msecs) + 1;
return wait_for_completion_interruptible_timeout(&rng->dying, timeout);
}
EXPORT_SYMBOL_GPL(hwrng_msleep);
long hwrng_yield(struct hwrng *rng)
{
return wait_for_completion_interruptible_timeout(&rng->dying, 1);
}
EXPORT_SYMBOL_GPL(hwrng_yield);
static int __init hwrng_modinit(void)
{
int ret;
/* 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();
}
fs_initcall(hwrng_modinit); /* depends on misc_register() */
module_exit(hwrng_modexit);
MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
MODULE_LICENSE("GPL");