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Diffstat (limited to 'arch/arm64/include/asm/archrandom.h')
| -rw-r--r-- | arch/arm64/include/asm/archrandom.h | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h new file mode 100644 index 000000000..109e2a445 --- /dev/null +++ b/arch/arm64/include/asm/archrandom.h @@ -0,0 +1,160 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_ARCHRANDOM_H +#define _ASM_ARCHRANDOM_H + +#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) +{ + bool ok; + + /* + * Reads of RNDR set PSTATE.NZCV to 0b0000 on success, + * and set PSTATE.NZCV to 0b0100 otherwise. + */ + asm volatile( + __mrs_s("%0", SYS_RNDR_EL0) "\n" + " cset %w1, ne\n" + : "=r" (*v), "=r" (ok) + : + : "cc"); + + return ok; +} + +static inline bool __arm64_rndrrs(unsigned long *v) +{ + bool ok; + + /* + * Reads of RNDRRS set PSTATE.NZCV to 0b0000 on success, + * and set PSTATE.NZCV to 0b0100 otherwise. + */ + asm volatile( + __mrs_s("%0", SYS_RNDRRS_EL0) "\n" + " cset %w1, ne\n" + : "=r" (*v), "=r" (ok) + : + : "cc"); + + return ok; +} + +static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs) +{ + /* + * 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 (max_longs && cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v)) + return 1; + return 0; +} + +static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs) +{ + if (!max_longs) + return 0; + + /* + * 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) { + struct arm_smccc_res res; + + max_longs = min_t(size_t, 3, max_longs); + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res); + if ((int)res.a0 >= 0) { + switch (max_longs) { + case 3: + *v++ = res.a1; + fallthrough; + case 2: + *v++ = res.a2; + fallthrough; + case 1: + *v++ = res.a3; + break; + } + return max_longs; + } + } + + /* + * RNDRRS is not backed by an entropy source but by a DRBG that is + * reseeded after each invocation. This is not a 100% fit but good + * enough to implement this API if no other entropy source exists. + */ + if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndrrs(v)) + return 1; + + return 0; +} + +static inline bool __init __early_cpu_has_rndr(void) +{ + /* Open code as we run prior to the first call to cpufeature. */ + unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1); + return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf; +} + +static inline size_t __init __must_check +arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs) +{ + WARN_ON(system_state != SYSTEM_BOOTING); + + if (!max_longs) + return 0; + + if (smccc_trng_available) { + struct arm_smccc_res res; + + max_longs = min_t(size_t, 3, max_longs); + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res); + if ((int)res.a0 >= 0) { + switch (max_longs) { + case 3: + *v++ = res.a1; + fallthrough; + case 2: + *v++ = res.a2; + fallthrough; + case 1: + *v++ = res.a3; + break; + } + return max_longs; + } + } + + if (__early_cpu_has_rndr() && __arm64_rndr(v)) + return 1; + + return 0; +} +#define arch_get_random_seed_longs_early arch_get_random_seed_longs_early + +#endif /* _ASM_ARCHRANDOM_H */ |