Commit 38db9873 authored by Andre Przywara's avatar Andre Przywara Committed by Will Deacon
Browse files

arm64: Add support for SMCCC TRNG entropy source 



The ARM architected TRNG firmware interface, described in ARM spec
DEN0098, defines an ARM SMCCC based interface to a true random number
generator, provided by firmware.
This can be discovered via the SMCCC >=v1.1 interface, and provides
up to 192 bits of entropy per call.

Hook this SMC call into arm64's arch_get_random_*() implementation,
coming to the rescue when the CPU does not implement the ARM v8.5 RNG
system registers.

For the detection, we piggy back on the PSCI/SMCCC discovery (which gives
us the conduit to use (hvc/smc)), then try to call the
ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is
not implemented.

Reviewed-by: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarAndre Przywara <andre.przywara@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent a37e31fc

arch/arm64/include/asm/archrandom.h

+61 −11
Original line number Diff line number Diff line
@@ -4,13 +4,24 @@ 


#ifdef CONFIG_ARCH_RANDOM



#include <linux/arm-smccc.h>

#include <linux/bug.h>

#include <linux/kernel.h>

#include <asm/cpufeature.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;



	return res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION;

}



static inline bool __arm64_rndr(unsigned long *v)
@@ -43,26 +54,55 @@ static inline bool __must_check arch_get_random_int(unsigned int *v) 


static inline bool __must_check arch_get_random_seed_long(unsigned long *v)

{

	struct arm_smccc_res res;



	/*

	 * We prefer the SMCCC call, since its semantics (return actual

	 * hardware backed entropy) is closer to the idea behind this

	 * function here than what even the RNDRSS register provides

	 * (the output of a pseudo RNG freshly seeded by a TRNG).

	 */

	if (smccc_trng_available) {

		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);

		if ((int)res.a0 >= 0) {

			*v = res.a3;

			return true;

		}

	}



	/*

	 * Only support the generic interface after we have detected

	 * the system wide capability, avoiding complexity with the

	 * cpufeature code and with potential scheduling between CPUs

	 * with and without the feature.

	 */

	if (!cpus_have_const_cap(ARM64_HAS_RNG))

		return false;

	if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v))

		return true;



	return __arm64_rndr(v);

	return false;

}





static inline bool __must_check arch_get_random_seed_int(unsigned int *v)

{

	struct arm_smccc_res res;

	unsigned long val;

	bool ok = arch_get_random_seed_long(&val);



	if (smccc_trng_available) {

		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 32, &res);

		if ((int)res.a0 >= 0) {

			*v = res.a3 & GENMASK(31, 0);

			return true;

		}

	}



	if (cpus_have_const_cap(ARM64_HAS_RNG)) {

		if (__arm64_rndr(&val)) {

			*v = val;

	return ok;

			return true;

		}

	}



	return false;

}



static inline bool __init __early_cpu_has_rndr(void)
@@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long *v) 
{

	WARN_ON(system_state != SYSTEM_BOOTING);



	if (!__early_cpu_has_rndr())

		return false;

	if (smccc_trng_available) {

		struct arm_smccc_res res;



		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);

		if ((int)res.a0 >= 0) {

			*v = res.a3;

			return true;

		}

	}



	if (__early_cpu_has_rndr() && __arm64_rndr(v))

		return true;



	return __arm64_rndr(v);

	return false;

}

#define arch_get_random_seed_long_early arch_get_random_seed_long_early