Re: [PATCH v6 3/5] ARM: implement support for SMCCC TRNG entropy source

[Ard Biesheuvel <ardb@kernel.org>]

On Wed, 6 Jan 2021 at 11:35, Andre Przywara <andre.przywara@arm.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> Implement arch_get_random_seed_*() for ARM based on the firmware
> or hypervisor provided entropy source described in ARM DEN0098.
>
> This will make the kernel's random number generator consume entropy
> provided by this interface, at early boot, and periodically at
> runtime when reseeding.
>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Russell King <linux@armlinux.org.uk>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> [Andre: rework to be initialised by the SMCCC firmware driver]
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

I think this one could be dropped into rmk's patch tracker now, right?


> ---
>  arch/arm/Kconfig                  |  4 ++
>  arch/arm/include/asm/archrandom.h | 64 +++++++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 138248999df7..bfe642510b0a 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1644,6 +1644,10 @@ config STACKPROTECTOR_PER_TASK
>           Enable this option to switch to a different method that uses a
>           different canary value for each task.
>
> +config ARCH_RANDOM
> +       def_bool y
> +       depends on HAVE_ARM_SMCCC_DISCOVERY
> +
>  endmenu
>
>  menu "Boot options"
> diff --git a/arch/arm/include/asm/archrandom.h b/arch/arm/include/asm/archrandom.h
> index a8e84ca5c2ee..f3e96a5b65f8 100644
> --- a/arch/arm/include/asm/archrandom.h
> +++ b/arch/arm/include/asm/archrandom.h
> @@ -2,9 +2,73 @@
>  #ifndef _ASM_ARCHRANDOM_H
>  #define _ASM_ARCHRANDOM_H
>
> +#ifdef CONFIG_ARCH_RANDOM
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/kernel.h>
> +
> +#define ARM_SMCCC_TRNG_MIN_VERSION     0x10000UL
> +
> +extern bool smccc_trng_available;
> +
> +static inline bool __init smccc_probe_trng(void)
> +{
> +       struct arm_smccc_res res;
> +
> +       arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res);
> +       if ((s32)res.a0 < 0)
> +               return false;
> +       if (res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION) {
> +               /* double check that the 32-bit flavor is available */
> +               arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_FEATURES,
> +                                    ARM_SMCCC_TRNG_RND32,
> +                                    &res);
> +               if ((s32)res.a0 >= 0)
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
> +static inline bool __must_check arch_get_random_long(unsigned long *v)
> +{
> +       return false;
> +}
> +
> +static inline bool __must_check arch_get_random_int(unsigned int *v)
> +{
> +       return false;
> +}
> +
> +static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
> +{
> +       struct arm_smccc_res res;
> +
> +       if (smccc_trng_available) {
> +               arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND32, 8 * sizeof(*v), &res);
> +
> +               if (res.a0 != 0)
> +                       return false;
> +
> +               *v = res.a3;
> +               return true;
> +       }
> +
> +       return false;
> +}
> +
> +static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
> +{
> +       return arch_get_random_seed_long((unsigned long *)v);
> +}
> +
> +
> +#else /* !CONFIG_ARCH_RANDOM */
> +
>  static inline bool __init smccc_probe_trng(void)
>  {
>         return false;
>  }
>
> +#endif /* CONFIG_ARCH_RANDOM */
>  #endif /* _ASM_ARCHRANDOM_H */
> --
> 2.17.1
>