[PATCH 2/2] s390: provide hardware randomness from zcrypt card to /dev/random

[Torsten Duwe <duwe@lst.de>]

Running completely virtualised, system Z severely lacks good true random sources.
Gathering entropy in a virtual environment is difficult. To compensate, there is
specialised crypto hardware which includes a source for hardware randomness;
the zcrypt driver is able to access this random source. This patch adds a kernel
thread that feeds the rendom bits via the interface created with the previous patch.

Signed-off-by: Torsten Duwe <duwe@lst.de>

---
 zcrypt_api.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
--- a/drivers/s390/crypto/zcrypt_api.c
+++ b/drivers/s390/crypto/zcrypt_api.c
@@ -38,6 +38,8 @@
 #include <linux/atomic.h>
 #include <asm/uaccess.h>
 #include <linux/hw_random.h>
+#include <linux/kthread.h>
+#include <linux/delay.h>
 #include <linux/debugfs.h>
 #include <asm/debug.h>
 
@@ -99,6 +99,15 @@ static ssize_t zcrypt_online_store(struc
 
 	if (sscanf(buf, "%d\n", &online) != 1 || online < 0 || online > 1)
 		return -EINVAL;
+	if (zdev->ops->rng) {
+		if (zdev->online == 0 && online == 1) {
+               		zcrypt_rng_device_add();
+		}
+		if (zdev->online == 1 && online == 0) {
+			zcrypt_rng_device_remove();
+		}
+
+	}
 	zdev->online = online;
 	ZCRYPT_DBF_DEV(DBF_INFO, zdev, "dev%04xo%dman", zdev->ap_dev->qid,
 		       zdev->online);
@@ -1117,6 +1119,7 @@ static int zcrypt_rng_device_count;
 static u32 *zcrypt_rng_buffer;
 static int zcrypt_rng_buffer_index;
 static DEFINE_MUTEX(zcrypt_rng_mutex);
+static struct task_struct *zcrypt_hwrng_fill;
 
 static int zcrypt_rng_data_read(struct hwrng *rng, u32 *data)
 {
@@ -1141,6 +1144,36 @@ static struct hwrng zcrypt_rng_dev = {
 	.data_read	= zcrypt_rng_data_read,
 };
 
+static int zcrypt_hwrng_fillfn(void * unused)
+{
+	long rc;
+	
+	while (!kthread_should_stop()) {
+		rc = zcrypt_rng((char*)zcrypt_rng_buffer);
+		if (rc == -ENODEV || rc == -EINVAL|| rc == -ENOMEM) {
+			printk(KERN_ERR "zcrypt_rng unavailable: %ld", rc);
+			break;
+		}
+		if (rc == -EAGAIN || rc == -ERESTARTSYS) {
+			printk(KERN_DEBUG "zcrypt_rng interrupted: %ld", rc);
+			msleep_interruptible(1000);
+			continue;
+		}
+		if (rc == 0) {
+			printk(KERN_ERR "zcrypt_rng: no data available");
+			msleep_interruptible(10000);
+			continue;
+		}
+		if (rc < 0) {
+			printk(KERN_ERR "zcrypt_rng unknown error: %ld", rc);
+			break;
+		}
+		add_hwgenerator_randomness((void*)zcrypt_rng_buffer, rc);
+	}
+	zcrypt_hwrng_fill = 0;
+	return 0;
+}
+
 static int zcrypt_rng_device_add(void)
 {
 	int rc = 0;
@@ -1157,6 +1189,11 @@ static int zcrypt_rng_device_add(void)
 		if (rc)
 			goto out_free;
 		zcrypt_rng_device_count = 1;
+		zcrypt_hwrng_fill = kthread_run(zcrypt_hwrng_fillfn, NULL, "zc_hwrng");
+		if (zcrypt_hwrng_fill == ERR_PTR(-ENOMEM)) {
+			printk(KERN_ERR "zcrypt_hwrng_fill thread creation failed");
+			zcrypt_hwrng_fill = 0;
+		}
 	} else
 		zcrypt_rng_device_count++;
 	mutex_unlock(&zcrypt_rng_mutex);
@@ -1174,6 +1211,10 @@ static void zcrypt_rng_device_remove(voi
 	mutex_lock(&zcrypt_rng_mutex);
 	zcrypt_rng_device_count--;
 	if (zcrypt_rng_device_count == 0) {
+		if (zcrypt_hwrng_fill) {
+			kthread_stop(zcrypt_hwrng_fill);
+			zcrypt_hwrng_fill = 0;
+		}
 		hwrng_unregister(&zcrypt_rng_dev);
 		free_page((unsigned long) zcrypt_rng_buffer);
 	}