Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness updates from Ted Ts'o:
 "Cleanups and bug fixes to /dev/random, add a new getrandom(2) system
  call, which is a superset of OpenBSD's getentropy(2) call, for use
  with userspace crypto libraries such as LibreSSL.

  Also add the ability to have a kernel thread to pull entropy from
  hardware rng devices into /dev/random"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  hwrng: Pass entropy to add_hwgenerator_randomness() in bits, not bytes
  random: limit the contribution of the hw rng to at most half
  random: introduce getrandom(2) system call
  hw_random: fix sparse warning (NULL vs 0 for pointer)
  random: use registers from interrupted code for CPU's w/o a cycle counter
  hwrng: add per-device entropy derating
  hwrng: create filler thread
  random: add_hwgenerator_randomness() for feeding entropy from devices
  random: use an improved fast_mix() function
  random: clean up interrupt entropy accounting for archs w/o cycle counters
  random: only update the last_pulled time if we actually transferred entropy
  random: remove unneeded hash of a portion of the entropy pool
  random: always update the entropy pool under the spinlock

drivers/char/hw_random/core.c

@@ -38,6 +38,7 @@
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/miscdevice.h>
+#include <linux/kthread.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/random.h>
@@ -50,10 +51,22 @@
 
 
 static struct hwrng *current_rng;
+static struct task_struct *hwrng_fill;
 static LIST_HEAD(rng_list);
 static DEFINE_MUTEX(rng_mutex);
 static int data_avail;
-static u8 *rng_buffer;
+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 mill");
+module_param(default_quality, ushort, 0644);
+MODULE_PARM_DESC(default_quality,
+		 "default entropy content of hwrng per mill");
+
+static void start_khwrngd(void);
 
 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 			       int wait);
@@ -89,6 +102,15 @@ static inline int hwrng_init(struct hwrng *rng)
 			return ret;
 	}
 	add_early_randomness(rng);
+
+	current_quality = rng->quality ? : default_quality;
+	current_quality &= 1023;
+
+	if (current_quality == 0 && hwrng_fill)
+		kthread_stop(hwrng_fill);
+	if (current_quality > 0 && !hwrng_fill)
+		start_khwrngd();
+
 	return 0;
 }
 
@@ -325,6 +347,36 @@ err_misc_dereg:
 	goto out;
 }
 
+static int hwrng_fillfn(void *unused)
+{
+	long rc;
+
+	while (!kthread_should_stop()) {
+		if (!current_rng)
+			break;
+		rc = rng_get_data(current_rng, rng_fillbuf,
+				  rng_buffer_size(), 1);
+		if (rc <= 0) {
+			pr_warn("hwrng: no data available\n");
+			msleep_interruptible(10000);
+			continue;
+		}
+		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 (hwrng_fill == ERR_PTR(-ENOMEM)) {
+		pr_err("hwrng_fill thread creation failed");
+		hwrng_fill = NULL;
+	}
+}
+
 int hwrng_register(struct hwrng *rng)
 {
 	int err = -EINVAL;
@@ -343,6 +395,13 @@ int hwrng_register(struct hwrng *rng)
 		if (!rng_buffer)
 			goto out_unlock;
 	}
+	if (!rng_fillbuf) {
+		rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
+		if (!rng_fillbuf) {
+			kfree(rng_buffer);
+			goto out_unlock;
+		}
+	}
 
 	/* Must not register two RNGs with the same name. */
 	err = -EEXIST;
@@ -406,8 +465,11 @@ void hwrng_unregister(struct hwrng *rng)
 				current_rng = NULL;
 		}
 	}
-	if (list_empty(&rng_list))
+	if (list_empty(&rng_list)) {
 		unregister_miscdev();
+		if (hwrng_fill)
+			kthread_stop(hwrng_fill);
+	}
 
 	mutex_unlock(&rng_mutex);
 }
@@ -418,6 +480,7 @@ static void __exit hwrng_exit(void)
 	mutex_lock(&rng_mutex);
 	BUG_ON(current_rng);
 	kfree(rng_buffer);
+	kfree(rng_fillbuf);
 	mutex_unlock(&rng_mutex);
 }