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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Thu, 27 Dec 2018 19:28:15 +0100
Message-ID: <CAKv+Gu9ShfrBhfCuRK_L_ZtZ3KnN7Jb-4hcX9nSO7AYbT8V8LQ@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] hwrng: add OP-TEE based rng driver
To: Sumit Garg <sumit.garg@linaro.org>
Cc: "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        Devicetree List <devicetree@vger.kernel.org>, mpm@selenic.com,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jens Wiklander <jens.wiklander@linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Bhupesh Sharma <bhsharma@redhat.com>, tee-dev@lists.linaro.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-crypto-owner@vger.kernel.org

On Thu, 27 Dec 2018 at 12:08, Sumit Garg <sumit.garg@linaro.org> 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.
>
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> ---
>  MAINTAINERS                        |   5 +
>  drivers/char/hw_random/Kconfig     |  15 ++
>  drivers/char/hw_random/Makefile    |   1 +
>  drivers/char/hw_random/optee-rng.c | 273 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 294 insertions(+)
>  create mode 100644 drivers/char/hw_random/optee-rng.c
>

Hi Sumit,

I am having some trouble with this driver. Even though the firmware
manages to invoke the pseudo-TA, the kernel driver responds with

[   73.915971] tee_client_open_session failed, error: ffff0008

(note that I need to run teesupplicant or the insmod just hangs)

Also, I have some concerns about the DT dependency (see my comment on
the previous patch)
I will cc you on some patches I have to expose OP-TEE via ACPI (as
well as DT) as a platform device. I'd prefer it if we could do the
same for this driver in one way or the other.

> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0767f1d..fe0fb74 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11100,6 +11100,11 @@ M:     Jens Wiklander <jens.wiklander@linaro.org>
>  S:     Maintained
>  F:     drivers/tee/optee/
>
> +OP-TEE RANDOM NUMBER GENERATOR (RNG) DRIVER
> +M:     Sumit Garg <sumit.garg@linaro.org>
> +S:     Maintained
> +F:     drivers/char/hw_random/optee-rng.c
> +
>  OPA-VNIC DRIVER
>  M:     Dennis Dalessandro <dennis.dalessandro@intel.com>
>  M:     Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
> 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..8c63730
> --- /dev/null
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -0,0 +1,273 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2018 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/tee_drv.h>
> +#include <linux/uuid.h>
> +
> +#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_seesion_id;

session not seesion

> +
> +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 */
> +       inv_arg.func = TA_CMD_GET_ENTROPY;
> +       inv_arg.session = ta_rng_seesion_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           = "optee-rng",
> +       .init           = optee_rng_init,
> +       .cleanup        = optee_rng_cleanup,
> +       .read           = optee_rng_read,
> +};
> +
> +static const struct of_device_id optee_match[] = {
> +       { .compatible = "linaro,optee-tz" },
> +       {},
> +};
> +
> +static int get_optee_rng_uuid(uuid_t *ta_rng_uuid)
> +{
> +       struct device_node *fw_np;
> +       struct device_node *np;
> +       const char *uuid;
> +
> +       /* Node is supposed to be below /firmware */
> +       fw_np = of_find_node_by_name(NULL, "firmware");
> +       if (!fw_np)
> +               return -ENODEV;
> +
> +       np = of_find_matching_node(fw_np, optee_match);
> +       if (!np || !of_device_is_available(np))
> +               return -ENODEV;
> +
> +       if (of_property_read_string(np, "rng-uuid", &uuid)) {
> +               pr_warn("missing \"uuid\" property\n");
> +               return -ENXIO;
> +       }
> +

So, duplicating all of this is really not a good idea.

> +       if (uuid_parse(uuid, ta_rng_uuid)) {
> +               pr_warn("incorrect rng ta uuid\n");
> +               return -EINVAL;
> +       }
> +
> +       return 0;
> +}
> +
> +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 */
> +       inv_arg.func = TA_CMD_GET_RNG_INFO;
> +       inv_arg.session = ta_rng_seesion_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 __init mod_init(void)
> +{
> +       int ret = 0, err = -ENODEV;
> +       struct tee_ioctl_open_session_arg sess_arg = {0};
> +       uuid_t ta_rng_uuid = {0};
> +
> +       err = get_optee_rng_uuid(&ta_rng_uuid);
> +       if (err)
> +               return err;
> +
> +       /* 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, ta_rng_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_seesion_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_seesion_id);
> +out_ctx:
> +       tee_client_close_context(ctx);
> +
> +       return err;
> +}
> +
> +static void __exit mod_exit(void)
> +{
> +       tee_client_close_session(ctx, ta_rng_seesion_id);
> +       tee_client_close_context(ctx);
> +       hwrng_unregister(&optee_rng);
> +}
> +
> +module_init(mod_init);
> +module_exit(mod_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sumit Garg <sumit.garg@linaro.org>");
> +MODULE_DESCRIPTION("OP-TEE based random number generator driver");
> +MODULE_SOFTDEP("pre: optee");

This is also an indicator that the API design needs some work. If the
OP-TEE driver becomes a 'bus' driver of some sort, the child RNG
device (which is what this driver should bind to) will only exist if
a) the OP-TEE driver is loaded, and b) it has actually bound to the
/firmware/optee node.

> --
> 2.7.4
>