Re: [Tee-dev] [PATCH v2 4/4] hwrng: add OP-TEE based rng driver

[Joakim Bech]

On Thu, Jan 10, 2019 at 05:54:57PM +0530, Sumit Garg wrote:
> On ARM SoC's with TrustZone enabled, peripherals like entropy sources
> might not be accessible to normal world (linux in this case) and rather
> accessible to secure world (OP-TEE in this case) only. So this driver
> aims to provides a generic interface to OP-TEE based random number
> generator service.
> 
> This driver registers on TEE bus to interact with OP-TEE based rng
>
> device/service.
> 
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
>  MAINTAINERS                        |   5 +
>  drivers/char/hw_random/Kconfig     |  15 ++
>  drivers/char/hw_random/Makefile    |   1 +
>  drivers/char/hw_random/optee-rng.c | 272 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 293 insertions(+)
>  create mode 100644 drivers/char/hw_random/optee-rng.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 32d44447..502733c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11260,6 +11260,11 @@ M:	Jens Wiklander <jens.wiklander@xxxxxxxxxx>
>  S:	Maintained
>  F:	drivers/tee/optee/
>  
> +OP-TEE RANDOM NUMBER GENERATOR (RNG) DRIVER
> +M:	Sumit Garg <sumit.garg@xxxxxxxxxx>
> +S:	Maintained
> +F:	drivers/char/hw_random/optee-rng.c
> +
>  OPA-VNIC DRIVER
>  M:	Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
>  M:	Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx>
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index dac895d..25a7d8f 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -424,6 +424,21 @@ config HW_RANDOM_EXYNOS
>  	  will be called exynos-trng.
>  
>  	  If unsure, say Y.
> +
> +config HW_RANDOM_OPTEE
> +	tristate "OP-TEE based Random Number Generator support"
> +	depends on OPTEE
> +	default HW_RANDOM
> +	help
> +	  This  driver provides support for OP-TEE based Random Number
> +	  Generator on ARM SoCs where hardware entropy sources are not
> +	  accessible to normal world (Linux).
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called optee-rng.
> +
> +	  If unsure, say Y.
> +
>  endif # HW_RANDOM
>  
>  config UML_RANDOM
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index e35ec3c..7c9ef4a 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -38,3 +38,4 @@ obj-$(CONFIG_HW_RANDOM_CAVIUM) += cavium-rng.o cavium-rng-vf.o
>  obj-$(CONFIG_HW_RANDOM_MTK)	+= mtk-rng.o
>  obj-$(CONFIG_HW_RANDOM_S390) += s390-trng.o
>  obj-$(CONFIG_HW_RANDOM_KEYSTONE) += ks-sa-rng.o
> +obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o
> diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> new file mode 100644
> index 0000000..ebfe1f2c
> --- /dev/null
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -0,0 +1,272 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2018-2019 Linaro Ltd.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/of.h>
> +#include <linux/hw_random.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/tee_drv.h>
> +#include <linux/uuid.h>
> +
> +#define DRIVER_NAME "optee-rng"
> +
> +#define TEE_ERROR_HEALTH_TEST_FAIL	0x00000001
> +
> +/*
> + * TA_CMD_GET_ENTROPY - Get Entropy from RNG
> + *
> + * param[0] (inout memref) - Entropy buffer memory reference
> + * param[1] unused
> + * param[2] unused
> + * param[3] unused
> + *
> + * Result:
> + * TEE_SUCCESS - Invoke command success
> + * TEE_ERROR_BAD_PARAMETERS - Incorrect input param
> + * TEE_ERROR_NOT_SUPPORTED - Requested entropy size greater than size of pool
> + * TEE_ERROR_HEALTH_TEST_FAIL - Continuous health testing failed
> + */
> +#define TA_CMD_GET_ENTROPY		0x0
> +
> +/*
> + * TA_CMD_GET_RNG_INFO - Get RNG information
> + *
> + * param[0] (out value) - value.a: RNG data-rate in bytes per second
> + *                        value.b: Quality/Entropy per 1024 bit of data
> + * param[1] unused
> + * param[2] unused
> + * param[3] unused
> + *
> + * Result:
> + * TEE_SUCCESS - Invoke command success
> + * TEE_ERROR_BAD_PARAMETERS - Incorrect input param
> + */
> +#define TA_CMD_GET_RNG_INFO		0x1
> +
> +#define MAX_ENTROPY_REQ_SZ		(4 * 1024)
> +
> +static struct tee_context *ctx;
> +static struct tee_shm *entropy_shm_pool;
> +static u32 ta_rng_data_rate;
> +static u32 ta_rng_session_id;
> +
> +static size_t get_optee_rng_data(void *buf, size_t req_size)
> +{
> +	u32 ret = 0;
> +	u8 *rng_data = NULL;
> +	size_t rng_size = 0;
> +	struct tee_ioctl_invoke_arg inv_arg = {0};
> +	struct tee_param param[4] = {0};
> +
> +	/* Invoke TA_CMD_GET_RNG function of Trusted App */
>
TA_CMD_GET_ENTROPY?

> +	inv_arg.func = TA_CMD_GET_ENTROPY;
> +	inv_arg.session = ta_rng_session_id;
> +	inv_arg.num_params = 4;
> +
> +	/* Fill invoke cmd params */
> +	param[0].attr = TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INOUT;
>
> +	param[0].u.memref.shm = entropy_shm_pool;
> +	param[0].u.memref.size = req_size;
> +	param[0].u.memref.shm_offs = 0;
> +
> +	ret = tee_client_invoke_func(ctx, &inv_arg, param);
> +	if ((ret < 0) || (inv_arg.ret != 0)) {
> +		pr_err("TA_CMD_GET_ENTROPY invoke function error: %x\n",
> +		       inv_arg.ret);
> +		return 0;
> +	}
> +
> +	rng_data = tee_shm_get_va(entropy_shm_pool, 0);
> +	if (IS_ERR(rng_data)) {
> +		pr_err("tee_shm_get_va failed\n");
> +		return 0;
> +	}
> +
> +	rng_size = param[0].u.memref.size;
> +	memcpy(buf, rng_data, rng_size);
> +
> +	return rng_size;
> +}
> +
> +static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> +{
> +	u8 *data = buf;
> +	size_t read = 0, rng_size = 0;
> +	int timeout = 1;
> +
> +	if (max > MAX_ENTROPY_REQ_SZ)
> +		max = MAX_ENTROPY_REQ_SZ;
> +
> +	while (read == 0) {
> +		rng_size = get_optee_rng_data(data, (max - read));
> +
> +		data += rng_size;
> +		read += rng_size;
> +
> +		if (wait) {
> +			if (timeout-- == 0)
> +				return read;
> +			msleep((1000 * (max - read)) / ta_rng_data_rate);
> +		} else {
> +			return read;
> +		}
> +	}
> +
> +	return read;
> +}
> +
> +static int optee_rng_init(struct hwrng *rng)
> +{
> +	entropy_shm_pool = tee_shm_alloc(ctx, MAX_ENTROPY_REQ_SZ,
> +					 TEE_SHM_MAPPED | TEE_SHM_DMA_BUF);
> +	if (IS_ERR(entropy_shm_pool)) {
> +		pr_err("tee_shm_alloc failed\n");
> +		return PTR_ERR(entropy_shm_pool);
> +	}
> +
> +	return 0;
> +}
> +
> +static void optee_rng_cleanup(struct hwrng *rng)
> +{
> +	tee_shm_free(entropy_shm_pool);
> +}
> +
> +static struct hwrng optee_rng = {
> +	.name		= DRIVER_NAME,
> +	.init		= optee_rng_init,
> +	.cleanup	= optee_rng_cleanup,
> +	.read		= optee_rng_read,
> +};
> +
> +static int get_optee_rng_info(void)
> +{
> +	u32 ret = 0;
> +	struct tee_ioctl_invoke_arg inv_arg = {0};
> +	struct tee_param param[4] = {0};
> +
> +	/* Invoke TA_CMD_GET_RNG function of Trusted App */
>
TA_CMD_GET_RNG_INFO?

> +	inv_arg.func = TA_CMD_GET_RNG_INFO;
> +	inv_arg.session = ta_rng_session_id;
> +	inv_arg.num_params = 4;
> +
> +	/* Fill invoke cmd params */
> +	param[0].attr = TEE_IOCTL_PARAM_ATTR_TYPE_VALUE_OUTPUT;
> +
> +	ret = tee_client_invoke_func(ctx, &inv_arg, param);
> +	if ((ret < 0) || (inv_arg.ret != 0)) {
> +		pr_err("TA_CMD_GET_RNG_INFO invoke function error: %x\n",
> +		       inv_arg.ret);
> +		return -EINVAL;
> +	}
> +
> +	ta_rng_data_rate = param[0].u.value.a;
> +	optee_rng.quality = param[0].u.value.b;
> +
> +	return 0;
> +}
> +
> +static int optee_ctx_match(struct tee_ioctl_version_data *ver, const void *data)
> +{
> +	if (ver->impl_id == TEE_IMPL_ID_OPTEE)
> +		return 1;
> +	else
> +		return 0;
> +}
> +
> +static int optee_rng_probe(struct device *dev)
> +{
> +	struct tee_client_device *rng_device = to_tee_client_device(dev);
> +	int ret = 0, err = -ENODEV;
> +	struct tee_ioctl_open_session_arg sess_arg = {0};
> +
> +	/* Open context with TEE driver */
> +	ctx = tee_client_open_context(NULL, optee_ctx_match, NULL, NULL);
> +	if (IS_ERR(ctx))
> +		return -ENODEV;
> +
> +	/* Open session with hwrng Trusted App */
> +	memcpy(sess_arg.uuid, rng_device->id.uuid.b, TEE_IOCTL_UUID_LEN);
> +	sess_arg.clnt_login = TEE_IOCTL_LOGIN_PUBLIC;
> +	sess_arg.num_params = 0;
> +
> +	ret = tee_client_open_session(ctx, &sess_arg, NULL);
> +	if ((ret < 0) || (sess_arg.ret != 0)) {
> +		pr_err("tee_client_open_session failed, error: %x\n",
> +		       sess_arg.ret);
> +		err = -EINVAL;
> +		goto out_ctx;
> +	}
> +	ta_rng_session_id = sess_arg.session;
> +
> +	err = get_optee_rng_info();
> +	if (err)
> +		goto out_sess;
> +
> +	err = hwrng_register(&optee_rng);
> +	if (err) {
> +		pr_err("registering failed (%d)\n", err);
> +		goto out_sess;
> +	}
> +
> +	return 0;
> +
> +out_sess:
> +	tee_client_close_session(ctx, ta_rng_session_id);
> +out_ctx:
> +	tee_client_close_context(ctx);
> +
> +	return err;
> +}
> +
> +static int optee_rng_remove(struct device *dev)
> +{
> +	tee_client_close_session(ctx, ta_rng_session_id);
> +	tee_client_close_context(ctx);
> +	hwrng_unregister(&optee_rng);
> +
> +	return 0;
> +}
> +
> +const struct tee_client_device_id optee_rng_id_table[] = {
> +	{UUID_INIT(0xab7a617c, 0xb8e7, 0x4d8f,
> +		   0x83, 0x01, 0xd0, 0x9b, 0x61, 0x03, 0x6b, 0x64)},
> +	{}
> +};
>
Just so I'm with you here, in the v1 patch set you said, that this could be
populated with other platform specific RNG UUID/GUID later. So if I implement
another RNG TA for another device in OP-TEE, then I only need to update this
array with another corresponding ID? To me it looks like the ta_rng_session_id
just stores an id for a single TEE RNG source, correct? I.e., this patch set is
not really written to fully support more than a single source in OP-TEE at this
point? I.e., my assumption about just adding another UUID to the array is wrong?

> +
> +static struct tee_client_driver optee_rng_driver = {
> +	.id_table	= optee_rng_id_table,
> +	.driver		= {
> +		.name		= DRIVER_NAME,
> +		.bus		= &tee_bus_type,
> +		.probe		= optee_rng_probe,
> +		.remove		= optee_rng_remove,
> +	},
> +};
> +
> +static int __init mod_init(void)
> +{
> +	int rc;
> +
> +	rc = driver_register(&optee_rng_driver.driver);
> +	if (rc)
> +		pr_warn("driver registration failed, err: %d", rc);
> +
> +	return rc;
> +}
> +
> +static void __exit mod_exit(void)
> +{
> +	driver_unregister(&optee_rng_driver.driver);
> +}
> +
> +module_init(mod_init);
> +module_exit(mod_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sumit Garg <sumit.garg@xxxxxxxxxx>");
> +MODULE_DESCRIPTION("OP-TEE based random number generator driver");
> -- 
> 2.7.4
> 
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-- 
Regards,
Joakim