Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Wed, 27 Nov 2019 at 15:23, Neal Liu <neal.liu@mediatek.com> wrote:
>
> For MediaTek SoCs on ARMv8 with TrustZone enabled, peripherals like
> entropy sources is not accessible from normal world (linux) and
> rather accessible from secure world (ATF/TEE) only. This driver aims
> to provide a generic interface to ATF rng service.
>
> Signed-off-by: Neal Liu <neal.liu@mediatek.com>
> ---
>  drivers/char/hw_random/Kconfig       |   16 ++++++
>  drivers/char/hw_random/Makefile      |    1 +
>  drivers/char/hw_random/mtk-sec-rng.c |  103 ++++++++++++++++++++++++++++++++++
>  3 files changed, 120 insertions(+)
>  create mode 100644 drivers/char/hw_random/mtk-sec-rng.c
>
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index 25a7d8f..f08c852 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -398,6 +398,22 @@ config HW_RANDOM_MTK
>
>           If unsure, say Y.
>
> +config HW_RANDOM_MTK_SEC
> +       tristate "MediaTek Security Random Number Generator support"
> +       depends on HW_RANDOM
> +       depends on ARCH_MEDIATEK || COMPILE_TEST
> +       default HW_RANDOM
> +         help
> +         This driver provides kernel-side support for the Random Number
> +         Generator hardware found on MediaTek SoCs. The difference with
> +         mtk-rng is the Random Number Generator hardware is secure
> +         access only.
> +
> +         To compile this driver as a module, choose M here. the
> +         module will be called mtk-sec-rng.
> +
> +         If unsure, say Y.
> +
>  config HW_RANDOM_S390
>         tristate "S390 True Random Number Generator support"
>         depends on S390
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index 7c9ef4a..bee5412 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -36,6 +36,7 @@ obj-$(CONFIG_HW_RANDOM_PIC32) += pic32-rng.o
>  obj-$(CONFIG_HW_RANDOM_MESON) += meson-rng.o
>  obj-$(CONFIG_HW_RANDOM_CAVIUM) += cavium-rng.o cavium-rng-vf.o
>  obj-$(CONFIG_HW_RANDOM_MTK)    += mtk-rng.o
> +obj-$(CONFIG_HW_RANDOM_MTK_SEC)        += mtk-sec-rng.o
>  obj-$(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/mtk-sec-rng.c b/drivers/char/hw_random/mtk-sec-rng.c
> new file mode 100644
> index 0000000..69ddeca
> --- /dev/null
> +++ b/drivers/char/hw_random/mtk-sec-rng.c
> @@ -0,0 +1,103 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 MediaTek Inc.
> + */
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/hw_random.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/soc/mediatek/mtk_sip_svc.h>
> +
> +#define MTK_SEC_RNG_MAGIC      0x74726e67
> +#define SMC_RET_NUM            4
> +#define MTK_SEC_RND_SIZE       (sizeof(u32) * SMC_RET_NUM)
> +
> +static void mtk_sec_get_rnd(uint32_t *val)
> +{
> +       struct arm_smccc_res res;
> +
> +       arm_smccc_smc(MTK_SIP_KERNEL_GET_RND,
> +                     MTK_SEC_RNG_MAGIC, 0, 0, 0, 0, 0, 0, &res);
> +

Can this call never fail? How does the firmware signal that something
is wrong with the underlying hardware?

> +       val[0] = res.a0;
> +       val[1] = res.a1;
> +       val[2] = res.a2;
> +       val[3] = res.a3;
> +}
> +
> +static int mtk_sec_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> +{
> +       u32 val[4] = {0};
> +       int retval = 0;
> +       int i;
> +
> +       while (max >= MTK_SEC_RND_SIZE) {
> +               mtk_sec_get_rnd(val);
> +
> +               for (i = 0; i < SMC_RET_NUM; i++) {
> +                       *(u32 *)buf = val[i];
> +                       buf += sizeof(u32);
> +               }
> +
> +               retval += MTK_SEC_RND_SIZE;
> +               max -= MTK_SEC_RND_SIZE;
> +       }
> +
> +       return retval;
> +}
> +
> +static struct hwrng mtk_sec_rng = {
> +       .name = "mtk_sec_rng",
> +       .read = mtk_sec_rng_read,
> +       .quality = 900,
> +};
> +
> +static int mtk_sec_rng_probe(void)
> +{
> +       int ret;
> +
> +       ret = hwrng_register(&mtk_sec_rng);
> +       if (ret) {
> +               pr_err("Failed to register rng device: %d\n", ret);
> +               return ret;
> +       }
> +
> +       return 0;
> +}
> +
> +static int __init mtk_sec_rng_driver_init(void)
> +{
> +       struct device_node *fw_np;
> +       struct device_node *np;
> +       const char *method;
> +
> +       fw_np = of_find_node_by_name(NULL, "firmware");
> +       if (!fw_np)
> +               return -ENODEV;
> +
> +       np = of_find_compatible_node(fw_np, NULL, "mediatek,mtk-sec-rng");
> +       if (!np)
> +               return -ENODEV;
> +
> +       if (of_property_read_string(np, "method", &method))
> +               return -ENXIO;
> +
> +       if (strncmp("smc", method, strlen("smc")))
> +               return -EINVAL;
> +
> +       return mtk_sec_rng_probe();
> +}
> +
> +static void __exit mtk_sec_rng_driver_exit(void)
> +{
> +       hwrng_unregister(&mtk_sec_rng);
> +}
> +
> +module_init(mtk_sec_rng_driver_init);
> +module_exit(mtk_sec_rng_driver_exit);
> +
> +MODULE_DESCRIPTION("MediaTek Security Random Number Generator Driver");
> +MODULE_AUTHOR("Neal Liu <neal.liu@mediatek.com>");
> +MODULE_LICENSE("GPL");
> --
> 1.7.9.5

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