/* 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 */