[PATCH v4 0/7] upstream hwrng framework

[PATCH v4 0/7] upstream hwrng framework

[Oleksij Rempel]

changes v1:
 - initial version

changes v2:
 - drop Freescale RNGC for now. It need more testing
 - add caamrng port
 - fix hwrng_init()
 - fix hwrng_get_first check in get_random_bytes

changes v3:
 - check if hwrng_get_data returns error
 - provide /dev/randomdd random device

changes v4:
 - provide get_crypto_bytes() interface.
 - add CONFIG_ALLOW_PRNG_FALLBACK
 - make cmd_password use get_crypto_bytes
 - add cmd_seed

Oleksij Rempel (5):
  caamrng: port to hwrng framework
  fs: add prng device
  crypto: caam - fix RNG buffer cache alignment
  common: password: make use of get_crypto_bytes
  add seed command

Steffen Trumtrar (2):
  drivers: add simple hw_random implementation
  lib: random: get_random_bytes from HWRNG if present

 commands/Kconfig              |   6 +++
 commands/Makefile             |   1 +
 commands/seed.c               |  48 +++++++++++++++++++
 commands/stddev.c             |  29 ++++++++++++
 common/password.c             |   6 ++-
 drivers/Kconfig               |   1 +
 drivers/Makefile              |   1 +
 drivers/crypto/caam/Kconfig   |   1 +
 drivers/crypto/caam/caamrng.c |  44 ++++++-----------
 drivers/hw_random/Kconfig     |   6 +++
 drivers/hw_random/Makefile    |   1 +
 drivers/hw_random/core.c      | 108 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/hw_random.h     |  43 +++++++++++++++++
 include/stdlib.h              |   1 +
 lib/Kconfig                   |   9 ++++
 lib/random.c                  |  58 +++++++++++++++++++++++
 16 files changed, 333 insertions(+), 30 deletions(-)
 create mode 100644 commands/seed.c
 create mode 100644 drivers/hw_random/Kconfig
 create mode 100644 drivers/hw_random/Makefile
 create mode 100644 drivers/hw_random/core.c
 create mode 100644 include/linux/hw_random.h

-- 
2.11.0


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[PATCH v4 1/7] drivers: add simple hw_random implementation

[Oleksij Rempel]

From: Steffen Trumtrar <s.trumtrar@pengutronix.de>

Add a simple hw_random implementation based on code from
Linux v4.5-rc5.

All the entropypool initialization stuff is left out and
the obsolete data_read/data_present calls are omitted.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/Kconfig            |   1 +
 drivers/Makefile           |   1 +
 drivers/hw_random/Kconfig  |   6 +++
 drivers/hw_random/Makefile |   1 +
 drivers/hw_random/core.c   | 108 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/hw_random.h  |  43 ++++++++++++++++++
 6 files changed, 160 insertions(+)
 create mode 100644 drivers/hw_random/Kconfig
 create mode 100644 drivers/hw_random/Makefile
 create mode 100644 drivers/hw_random/core.c
 create mode 100644 include/linux/hw_random.h

diff --git a/drivers/Kconfig b/drivers/Kconfig
index cc086ac2d..2f5784a4d 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -21,6 +21,7 @@ source "drivers/eeprom/Kconfig"
 source "drivers/input/Kconfig"
 source "drivers/watchdog/Kconfig"
 source "drivers/pwm/Kconfig"
+source "drivers/hw_random/Kconfig"
 source "drivers/dma/Kconfig"
 source "drivers/gpio/Kconfig"
 source "drivers/w1/Kconfig"
diff --git a/drivers/Makefile b/drivers/Makefile
index 6a70f6ee1..7e9b80e59 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -20,6 +20,7 @@ obj-y	+= misc/
 obj-y	+= dma/
 obj-y  += watchdog/
 obj-y	+= gpio/
+obj-$(CONFIG_HWRNG) += hw_random/
 obj-$(CONFIG_OFTREE) += of/
 obj-$(CONFIG_W1) += w1/
 obj-y += pinctrl/
diff --git a/drivers/hw_random/Kconfig b/drivers/hw_random/Kconfig
new file mode 100644
index 000000000..807fcadd3
--- /dev/null
+++ b/drivers/hw_random/Kconfig
@@ -0,0 +1,6 @@
+menuconfig HWRNG
+	bool "HWRNG Support"
+	help
+	  Support for HWRNG(Hardware Random Number Generator) devices.
+
+	  If unsure, say no.
diff --git a/drivers/hw_random/Makefile b/drivers/hw_random/Makefile
new file mode 100644
index 000000000..15307b100
--- /dev/null
+++ b/drivers/hw_random/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_HWRNG)		+= core.o
diff --git a/drivers/hw_random/core.c b/drivers/hw_random/core.c
new file mode 100644
index 000000000..2991f58c3
--- /dev/null
+++ b/drivers/hw_random/core.c
@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2016 Pengutronix, Steffen Trumtrar <kernel@pengutronix.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * derived from Linux kernel drivers/char/hw_random/core.c
+ */
+
+#include <common.h>
+#include <linux/hw_random.h>
+#include <malloc.h>
+
+static LIST_HEAD(hwrngs);
+
+#define RNG_BUFFER_SIZE		32
+
+int hwrng_get_data(struct hwrng *rng, void *buffer, size_t size, int wait)
+{
+	return rng->read(rng, buffer, size, wait);
+}
+
+static int hwrng_init(struct hwrng *rng)
+{
+	int ret = 0;
+
+	if (rng->init)
+		ret = rng->init(rng);
+
+	if (!ret)
+		list_add_tail(&rng->list, &hwrngs);
+
+	return ret;
+}
+
+static ssize_t rng_dev_read(struct cdev *cdev, void *buf, size_t size,
+			    loff_t offset, unsigned long flags)
+{
+	struct hwrng *rng = container_of(cdev, struct hwrng, cdev);
+	size_t count = size;
+	ssize_t cur = 0;
+	int len;
+
+	memset(buf, 0, size);
+
+	while (count) {
+		int max = min(count, (size_t)RNG_BUFFER_SIZE);
+		len = hwrng_get_data(rng, rng->buf, max, true);
+		if (len < 0) {
+			cur = len;
+			break;
+		}
+
+		memcpy(buf + cur, rng->buf, len);
+
+		count -= len;
+		cur += len;
+	}
+
+	return cur;
+}
+
+static struct file_operations rng_chrdev_ops = {
+	.read  = rng_dev_read,
+	.lseek = dev_lseek_default,
+};
+
+static int hwrng_register_cdev(struct hwrng *rng)
+{
+	rng->cdev.name = "hwrng";
+	rng->cdev.flags = DEVFS_IS_CHARACTER_DEV;
+	rng->cdev.ops = &rng_chrdev_ops;
+	rng->cdev.dev = rng->dev;
+
+	return devfs_create(&rng->cdev);
+}
+
+struct hwrng *hwrng_get_first(void)
+{
+	if (list_empty(&hwrngs))
+		return ERR_PTR(-ENODEV);
+	else
+		return list_first_entry(&hwrngs, struct hwrng, list);
+}
+
+int hwrng_register(struct device_d *dev, struct hwrng *rng)
+{
+	int err;
+
+	if (rng->name == NULL || rng->read == NULL)
+		return -EINVAL;
+
+	rng->buf = xzalloc(RNG_BUFFER_SIZE);
+	rng->dev = dev;
+
+	err = hwrng_init(rng);
+	if (err) {
+		free(rng->buf);
+		return err;
+	}
+
+	err = hwrng_register_cdev(rng);
+	if (err)
+		free(rng->buf);
+
+	return err;
+}
diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h
new file mode 100644
index 000000000..299a717dd
--- /dev/null
+++ b/include/linux/hw_random.h
@@ -0,0 +1,43 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef LINUX_HWRANDOM_H_
+#define LINUX_HWRANDOM_H_
+
+#include <linux/list.h>
+
+/**
+ * struct hwrng - Hardware Random Number Generator driver
+ * @name:		Unique RNG name.
+ * @init:		Initialization callback (can be NULL).
+ * @read:		New API. drivers can fill up to max bytes of data
+ *			into the buffer. The buffer is aligned for any type.
+ * @priv:		Private data, for use by the RNG driver.
+ */
+struct hwrng {
+	const char *name;
+	int (*init)(struct hwrng *rng);
+	int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);
+
+	struct list_head list;
+
+	struct cdev cdev;
+	struct device_d *dev;
+	void *buf;
+};
+
+/* Register a new Hardware Random Number Generator driver. */
+int hwrng_register(struct device_d *dev, struct hwrng *rng);
+struct hwrng *hwrng_get_first(void);
+int hwrng_get_data(struct hwrng *rng, void *buffer, size_t size, int wait);
+
+#endif /* LINUX_HWRANDOM_H_ */
-- 
2.11.0


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[PATCH v4 2/7] lib: random: get_random_bytes from HWRNG if present

[Oleksij Rempel]

From: Steffen Trumtrar <s.trumtrar@pengutronix.de>

Instead of generating pseudo random numbers, get random bytes
from an optional HW generator, if enabled and registered.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 include/stdlib.h |  1 +
 lib/Kconfig      |  9 +++++++++
 lib/random.c     | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+)

diff --git a/include/stdlib.h b/include/stdlib.h
index f3185069f..ee3f22996 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -13,6 +13,7 @@ void srand(unsigned int seed);
 
 /* fill a buffer with pseudo-random data */
 void get_random_bytes(void *buf, int len);
+int get_crypto_bytes(void *buf, int len);
 
 static inline u32 random32(void)
 {
diff --git a/lib/Kconfig b/lib/Kconfig
index f9f25bdef..c16511c05 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -66,6 +66,15 @@ config RATP
 	  transferring packets over serial links described in RFC916. This implementation
 	  is used for controlling barebox over serial ports.
 
+config ALLOW_PRNG_FALLBACK
+	bool "Allow fallback to PRNG if HWRNG not available."
+	help
+	  WARNING: it is not secure!!
+
+	  get_crypto_bytes() users like cmd_password relay on HWRNG. If HWRNG is not
+	  available and this option is disabled, cmd_password will fail.
+	  Enable it on your own risk.
+
 source lib/gui/Kconfig
 
 source lib/fonts/Kconfig
diff --git a/lib/random.c b/lib/random.c
index 210fea994..fa1fa5606 100644
--- a/lib/random.c
+++ b/lib/random.c
@@ -1,5 +1,6 @@
 #include <common.h>
 #include <stdlib.h>
+#include <linux/hw_random.h>
 
 static unsigned int random_seed;
 
@@ -18,6 +19,11 @@ void srand(unsigned int seed)
 	random_seed = seed;
 }
 
+/**
+ * get_random_bytes - get pseudo random numbers.
+ * This interface can be good enough to generate MAC address
+ * or use for NAND test.
+ */
 void get_random_bytes(void *_buf, int len)
 {
 	char *buf = _buf;
@@ -25,3 +31,55 @@ void get_random_bytes(void *_buf, int len)
 	while (len--)
 		*buf++ = rand() % 256;
 }
+
+/**
+ * get_crypto_bytes - get random numbers suitable for cryptographic needs.
+ */
+static int _get_crypto_bytes(void *_buf, int len)
+{
+	struct hwrng *rng;
+	u8 *buf = _buf;
+
+	if (!IS_ENABLED(CONFIG_HWRNG))
+		return -ENOENT;
+
+	rng = hwrng_get_first();
+	if (IS_ERR(rng))
+		return PTR_ERR(rng);
+
+	while (len) {
+		int bytes = hwrng_get_data(rng, buf, len, true);
+		if (!bytes)
+			return -ENOMEDIUM;
+
+		if (bytes < 0)
+			return bytes;
+
+		if (bytes > len)
+			bytes = len;
+		len -= bytes;
+		buf = buf + bytes;
+	}
+
+	return 0;
+}
+
+int get_crypto_bytes(void *buf, int len)
+{
+	int err;
+
+	err = _get_crypto_bytes(buf, len);
+	if (!err)
+		return 0;
+
+	if (!IS_ENABLED(CONFIG_ALLOW_PRNG_FALLBACK)) {
+		pr_err("error: no HWRNG available!\n");
+		return err;
+	}
+
+	pr_warn("warning: falling back to Pseudo RNG source!\n");
+
+	get_random_bytes(buf, len);
+
+	return 0;
+}
-- 
2.11.0


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[PATCH v4 3/7] caamrng: port to hwrng framework

[Oleksij Rempel]

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/crypto/caam/Kconfig   |  1 +
 drivers/crypto/caam/caamrng.c | 40 ++++++++++++----------------------------
 2 files changed, 13 insertions(+), 28 deletions(-)

diff --git a/drivers/crypto/caam/Kconfig b/drivers/crypto/caam/Kconfig
index cf05d1c07..2ab509d11 100644
--- a/drivers/crypto/caam/Kconfig
+++ b/drivers/crypto/caam/Kconfig
@@ -29,6 +29,7 @@ config CRYPTO_DEV_FSL_CAAM_RINGSIZE
 config CRYPTO_DEV_FSL_CAAM_RNG
 	bool "Register caam RNG device"
 	depends on CRYPTO_DEV_FSL_CAAM
+	depends on HWRNG
 	default y
 	help
 	  Selecting this will register the SEC4 hardware rng.
diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
index 0fef171a2..aabad0416 100644
--- a/drivers/crypto/caam/caamrng.c
+++ b/drivers/crypto/caam/caamrng.c
@@ -35,6 +35,7 @@
 #include <driver.h>
 #include <init.h>
 #include <linux/spinlock.h>
+#include <linux/hw_random.h>
 
 #include "regs.h"
 #include "intern.h"
@@ -71,7 +72,7 @@ struct caam_rng_ctx {
 	unsigned int cur_buf_idx;
 	int current_buf;
 	struct buf_data bufs[2];
-	struct cdev cdev;
+	struct hwrng rng;
 };
 
 static struct caam_rng_ctx *rng_ctx;
@@ -116,8 +117,9 @@ static inline int submit_job(struct caam_rng_ctx *ctx, int to_current)
 	return err;
 }
 
-static int caam_read(struct caam_rng_ctx *ctx, void *data, size_t max, bool wait)
+static int caam_read(struct hwrng *rng, void *data, size_t max, bool wait)
 {
+	struct caam_rng_ctx *ctx = container_of(rng, struct caam_rng_ctx, rng);
 	struct buf_data *bd = &ctx->bufs[ctx->current_buf];
 	int next_buf_idx, copied_idx;
 	int err;
@@ -162,7 +164,7 @@ static int caam_read(struct caam_rng_ctx *ctx, void *data, size_t max, bool wait
 	dev_dbg(ctx->jrdev, "switched to buffer %d\n", ctx->current_buf);
 
 	/* since there already is some data read, don't wait */
-	return copied_idx + caam_read(ctx, data + copied_idx,
+	return copied_idx + caam_read(rng, data + copied_idx,
 				      max - copied_idx, false);
 }
 
@@ -248,29 +250,6 @@ static int caam_init_rng(struct caam_rng_ctx *ctx, struct device_d *jrdev)
 	return 0;
 }
 
-static ssize_t random_read(struct cdev *cdev, void *buf, size_t count,
-			   loff_t offset, ulong flags)
-{
-	struct caam_rng_ctx *ctx = container_of(cdev, struct caam_rng_ctx, cdev);
-
-	return caam_read(ctx, buf, count, true);
-}
-
-static struct file_operations randomops = {
-	.read  = random_read,
-	.lseek = dev_lseek_default,
-};
-
-static int caam_init_devrandom(struct caam_rng_ctx *ctx, struct device_d *dev)
-{
-	ctx->cdev.name = "hwrng";
-	ctx->cdev.flags = DEVFS_IS_CHARACTER_DEV;
-	ctx->cdev.ops = &randomops;
-	ctx->cdev.dev = dev;
-
-	return devfs_create(&ctx->cdev);
-}
-
 int caam_rng_probe(struct device_d *dev, struct device_d *jrdev)
 {
 	int err;
@@ -281,9 +260,14 @@ int caam_rng_probe(struct device_d *dev, struct device_d *jrdev)
 	if (err)
 		return err;
 
-	err = caam_init_devrandom(rng_ctx, dev);
-	if (err)
+	rng_ctx->rng.name = dev->name;
+	rng_ctx->rng.read = caam_read;
+
+	err = hwrng_register(dev, &rng_ctx->rng);
+	if (err) {
+		dev_err(dev, "rng-caam registering failed (%d)\n", err);
 		return err;
+	}
 
 	dev_info(dev, "registering rng-caam\n");
 
-- 
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[PATCH v4 4/7] fs: add prng device

[Oleksij Rempel]

this should provide easy access to get_random_bytes() interfaces.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 commands/stddev.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/commands/stddev.c b/commands/stddev.c
index 318d05741..93da2c739 100644
--- a/commands/stddev.c
+++ b/commands/stddev.c
@@ -17,6 +17,7 @@
 
 #include <common.h>
 #include <init.h>
+#include <stdlib.h>
 
 static ssize_t zero_read(struct cdev *cdev, void *buf, size_t count, loff_t offset, ulong flags)
 {
@@ -100,3 +101,31 @@ static int null_init(void)
 }
 
 device_initcall(null_init);
+
+static ssize_t prng_read(struct cdev *cdev, void *buf, size_t count, loff_t offset, ulong flags)
+{
+	get_random_bytes(buf, count);
+	return count;
+}
+
+static struct file_operations prngops = {
+	.read  = prng_read,
+	.lseek = dev_lseek_default,
+};
+
+static int prng_init(void)
+{
+	struct cdev *cdev;
+
+	cdev = xzalloc(sizeof (*cdev));
+
+	cdev->name = "prng";
+	cdev->flags = DEVFS_IS_CHARACTER_DEV;
+	cdev->ops = &prngops;
+
+	devfs_create(cdev);
+
+	return 0;
+}
+
+device_initcall(prng_init);
-- 
2.11.0


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[PATCH v4 5/7] crypto: caam - fix RNG buffer cache alignment

[Oleksij Rempel]

this is alternate version of linux fix:
---------------------------------------------------------------------
The hwrng output buffers (2) are cast inside of a a struct
(caam_rng_ctx)
allocated in one DMA-tagged region. While the kernel's heap allocator
should place the overall struct on a cacheline aligned boundary, the 2
buffers contained within may not necessarily align. Consenquently, the
ends
of unaligned buffers may not fully flush, and if so, stale data will be
left
behind, resulting in small repeating patterns.

This fix aligns the buffers inside the struct.

Note that not all of the data inside caam_rng_ctx necessarily needs to
be
DMA-tagged, only the buffers themselves require this. However, a fix
would
incur the expense of error-handling bloat in the case of allocation
failure.

Cc: stable@vger.kernel.org
Signed-off-by: Steve Cornelius <steve.cornelius@freescale.com>
Signed-off-by: Victoria Milhoan <vicki.milhoan@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---------------------------------------------------------------------

instead we will use just dma_alloc()

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/crypto/caam/caamrng.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
index aabad0416..31a92731d 100644
--- a/drivers/crypto/caam/caamrng.c
+++ b/drivers/crypto/caam/caamrng.c
@@ -55,7 +55,7 @@
 
 /* Buffer, its dma address and lock */
 struct buf_data {
-	u8 buf[RN_BUF_SIZE];
+	u8 *buf;
 	dma_addr_t addr;
 	u32 hw_desc[DESC_JOB_O_LEN];
 #define BUF_NOT_EMPTY 0
@@ -218,6 +218,8 @@ static int caam_init_buf(struct caam_rng_ctx *ctx, int buf_id)
 	struct buf_data *bd = &ctx->bufs[buf_id];
 	int err;
 
+	bd->buf = dma_alloc(RN_BUF_SIZE);
+
 	err = rng_create_job_desc(ctx, buf_id);
 	if (err)
 		return err;
-- 
2.11.0


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[PATCH v4 6/7] common: password: make use of get_crypto_bytes

[Oleksij Rempel]

get_random_bytes is providing prng, if we have HWRNG we should be
able to use it over get_crypto_bytes

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 common/password.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/common/password.c b/common/password.c
index d52b746f0..74d328f4b 100644
--- a/common/password.c
+++ b/common/password.c
@@ -365,7 +365,11 @@ int set_env_passwd(unsigned char* passwd, size_t length)
 		char *salt = passwd_sum;
 		int keylen = PBKDF2_LENGTH - PBKDF2_SALT_LEN;
 
-		get_random_bytes(passwd_sum, PBKDF2_SALT_LEN);
+		ret = get_crypto_bytes(passwd_sum, PBKDF2_SALT_LEN);
+		if (ret) {
+			pr_err("Can't get random numbers\n");
+			return ret;
+		}
 
 		ret = pkcs5_pbkdf2_hmac_sha1(passwd, length, salt,
 				PBKDF2_SALT_LEN, PBKDF2_COUNT, keylen, key);
-- 
2.11.0


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[PATCH v4 7/7] add seed command

[Oleksij Rempel]

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 commands/Kconfig  |  6 ++++++
 commands/Makefile |  1 +
 commands/seed.c   | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 commands/seed.c

diff --git a/commands/Kconfig b/commands/Kconfig
index 21d921268..c983b62d0 100644
--- a/commands/Kconfig
+++ b/commands/Kconfig
@@ -2115,6 +2115,12 @@ config CMD_SPD_DECODE
 	help
 	  decode spd eeprom
 
+config CMD_SEED
+	tristate
+	prompt "seed"
+	help
+	  Seed the pseudo random number generator (PRNG)
+
 # end Miscellaneous commands
 endmenu
 
diff --git a/commands/Makefile b/commands/Makefile
index 601f15fc3..ab5902156 100644
--- a/commands/Makefile
+++ b/commands/Makefile
@@ -120,3 +120,4 @@ obj-$(CONFIG_CMD_DHRYSTONE)	+= dhrystone.o
 obj-$(CONFIG_CMD_SPD_DECODE)	+= spd_decode.o
 obj-$(CONFIG_CMD_MMC_EXTCSD)	+= mmc_extcsd.o
 obj-$(CONFIG_CMD_NAND_BITFLIP)	+= nand-bitflip.o
+obj-$(CONFIG_CMD_SEED)		+= seed.o
diff --git a/commands/seed.c b/commands/seed.c
new file mode 100644
index 000000000..288b48b09
--- /dev/null
+++ b/commands/seed.c
@@ -0,0 +1,48 @@
+/*
+ * (c) 2017 Oleksij Rempel <kernel@pengutronix.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <common.h>
+#include <command.h>
+#include <stdlib.h>
+#include <linux/ctype.h>
+
+static int do_seed(int argc, char *argv[])
+{
+	if (argc > 1) {
+		if (isdigit(*argv[1])) {
+			srand(simple_strtoul(argv[1], NULL, 0));
+		} else {
+			printf("numerical parameter expected\n");
+			return 1;
+		}
+	}
+
+	/* running rand() will influence prng as well, so it is part of seeding */
+	rand();
+
+	return 0;
+}
+
+BAREBOX_CMD_HELP_START(seed)
+BAREBOX_CMD_HELP_TEXT("Seed the pseudo random number generator")
+BAREBOX_CMD_HELP_TEXT("Without a parameter the PRNG will be reexecuted")
+BAREBOX_CMD_HELP_END
+
+BAREBOX_CMD_START(seed)
+	.cmd = do_seed,
+	BAREBOX_CMD_DESC("seed the PRNG")
+	BAREBOX_CMD_OPTS("[SEED]")
+	BAREBOX_CMD_GROUP(CMD_GRP_MISC)
+	BAREBOX_CMD_HELP(cmd_seed_help)
+BAREBOX_CMD_END
-- 
2.11.0


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