[PATCH v5 5/8] sandbox: rng: Add a random number generator(rng) driver

[Heinrich Schuchardt]

On 12/26/19 6:25 PM, Sughosh Ganu wrote:
> Add a sandbox driver for random number generation. Mostly aimed at
> providing a unit test for rng uclass.
>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> Reviewed-by: Patrice Chotard <patrice.chotard at st.com>
> ---
> Changes since V4:
> * Return number of bytes read on a successful read, and a -ve value on
>    error.
> * Modify the logic of sandbox_rng_read function to use rand and srand
>    functions to return random data, based on feedback from Heinrich
>    Schuchardt.
>
>   arch/sandbox/dts/test.dts |  4 ++++
>   drivers/rng/Kconfig       |  8 +++++++
>   drivers/rng/Makefile      |  1 +
>   drivers/rng/sandbox_rng.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 69 insertions(+)
>   create mode 100644 drivers/rng/sandbox_rng.c
>
> diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
> index fdb08f2..2c85540 100644
> --- a/arch/sandbox/dts/test.dts
> +++ b/arch/sandbox/dts/test.dts
> @@ -599,6 +599,10 @@
>   		reset-names = "other", "test";
>   	};
>
> +	rng at 0 {
> +		compatible = "sandbox,sandbox-rng";
> +	};
> +
>   	rproc_1: rproc at 1 {
>   		compatible = "sandbox,test-processor";
>   		remoteproc-name = "remoteproc-test-dev1";
> diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
> index c9c4751..35a3bd1 100644
> --- a/drivers/rng/Kconfig
> +++ b/drivers/rng/Kconfig
> @@ -6,6 +6,14 @@ config DM_RNG
>   	  This interface is used to initialise the rng device and to
>   	  read the random seed from the device.
>
> +config RNG_SANDBOX
> +	bool "Sandbox random number generator"
> +	depends on SANDBOX && DM_RNG
> +	select CONFIG_LIB_RAND
> +	help
> +	  Enable random number generator for sandbox. This is an
> +	  emulation of a rng device.
> +
>   config RNG_STM32MP1
>   	bool "Enable random number generator for STM32MP1"
>   	depends on ARCH_STM32MP && DM_RNG
> diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
> index 699beb3..3517005 100644
> --- a/drivers/rng/Makefile
> +++ b/drivers/rng/Makefile
> @@ -4,4 +4,5 @@
>   #
>
>   obj-$(CONFIG_DM_RNG) += rng-uclass.o
> +obj-$(CONFIG_RNG_SANDBOX) += sandbox_rng.o
>   obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o
> diff --git a/drivers/rng/sandbox_rng.c b/drivers/rng/sandbox_rng.c
> new file mode 100644
> index 0000000..5de1799
> --- /dev/null
> +++ b/drivers/rng/sandbox_rng.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2019, Linaro Limited
> + */
> +
> +#include <common.h>
> +#include <dm.h>
> +#include <rng.h>
> +
> +#include <linux/string.h>
> +
> +static int sandbox_rng_read(struct udevice *dev, void *data, size_t len)
> +{
> +	int nbytes;
> +	unsigned int i, seed;
> +	unsigned int *buf = data;

You assume here that data is 4 byte aligned which may not hold true and
hence may lead to a crash on ARM.

Best regards

Heinrich

> +	size_t nrem, nloops;
> +
> +	/*
> +	 * Only INT_MAX number of bytes can be returned. If more
> +	 * bytes need to be read, the caller must do it in a loop.
> +	 */
> +	if (len > INT_MAX)
> +		len = INT_MAX;
> +
> +	nbytes = len;
> +	nloops = len / sizeof(unsigned int);
> +	seed = get_timer(0) ^ rand();
> +	srand(seed);
> +
> +	for (i = 0, nrem = len; i < nloops; i++, nrem -= sizeof(unsigned int))
> +		*buf++ = rand();
> +
> +	seed = rand();
> +	memcpy(buf, &seed, nrem);
> +
> +	return nbytes;
> +}
> +
> +static const struct dm_rng_ops sandbox_rng_ops = {
> +	.read = sandbox_rng_read,
> +};
> +
> +static const struct udevice_id sandbox_rng_match[] = {
> +	{
> +		.compatible = "sandbox,sandbox-rng",
> +	},
> +	{},
> +};
> +
> +U_BOOT_DRIVER(sandbox_rng) = {
> +	.name = "sandbox-rng",
> +	.id = UCLASS_RNG,
> +	.of_match = sandbox_rng_match,
> +	.ops = &sandbox_rng_ops,
> +};
>