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| 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
|---|---|
| 2 | #ifndef _ASM_ARCHRANDOM_H |
| 3 | #define _ASM_ARCHRANDOM_H |
| 4 | |
| 5 | #include <linux/arm-smccc.h> |
| 6 | #include <linux/bug.h> |
| 7 | #include <linux/kernel.h> |
| 8 | #include <linux/irqflags.h> |
| 9 | #include <asm/cpufeature.h> |
| 10 | |
| 11 | #define ARM_SMCCC_TRNG_MIN_VERSION 0x10000UL |
| 12 | |
| 13 | extern bool smccc_trng_available; |
| 14 | |
| 15 | static inline bool __init smccc_probe_trng(void) |
| 16 | { |
| 17 | struct arm_smccc_res res; |
| 18 | |
| 19 | arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res); |
| 20 | if ((s32)res.a0 < 0) |
| 21 | return false; |
| 22 | |
| 23 | return res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION; |
| 24 | } |
| 25 | |
| 26 | static inline bool __arm64_rndr(unsigned long *v) |
| 27 | { |
| 28 | bool ok; |
| 29 | |
| 30 | /* |
| 31 | * Reads of RNDR set PSTATE.NZCV to 0b0000 on success, |
| 32 | * and set PSTATE.NZCV to 0b0100 otherwise. |
| 33 | */ |
| 34 | asm volatile( |
| 35 | __mrs_s("%0", SYS_RNDR_EL0) "\n" |
| 36 | " cset %w1, ne\n" |
| 37 | : "=r" (*v), "=r" (ok) |
| 38 | : |
| 39 | : "cc"); |
| 40 | |
| 41 | return ok; |
| 42 | } |
| 43 | |
| 44 | static inline bool __arm64_rndrrs(unsigned long *v) |
| 45 | { |
| 46 | bool ok; |
| 47 | |
| 48 | /* |
| 49 | * Reads of RNDRRS set PSTATE.NZCV to 0b0000 on success, |
| 50 | * and set PSTATE.NZCV to 0b0100 otherwise. |
| 51 | */ |
| 52 | asm volatile( |
| 53 | __mrs_s("%0", SYS_RNDRRS_EL0) "\n" |
| 54 | " cset %w1, ne\n" |
| 55 | : "=r" (*v), "=r" (ok) |
| 56 | : |
| 57 | : "cc"); |
| 58 | |
| 59 | return ok; |
| 60 | } |
| 61 | |
| 62 | static __always_inline bool __cpu_has_rng(void) |
| 63 | { |
| 64 | if (unlikely(!system_capabilities_finalized() && !preemptible())) |
| 65 | return this_cpu_has_cap(ARM64_HAS_RNG); |
| 66 | return alternative_has_cap_unlikely(ARM64_HAS_RNG); |
| 67 | } |
| 68 | |
| 69 | static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs) |
| 70 | { |
| 71 | /* |
| 72 | * Only support the generic interface after we have detected |
| 73 | * the system wide capability, avoiding complexity with the |
| 74 | * cpufeature code and with potential scheduling between CPUs |
| 75 | * with and without the feature. |
| 76 | */ |
| 77 | if (max_longs && __cpu_has_rng() && __arm64_rndr(v)) |
| 78 | return 1; |
| 79 | return 0; |
| 80 | } |
| 81 | |
| 82 | static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs) |
| 83 | { |
| 84 | if (!max_longs) |
| 85 | return 0; |
| 86 | |
| 87 | /* |
| 88 | * We prefer the SMCCC call, since its semantics (return actual |
| 89 | * hardware backed entropy) is closer to the idea behind this |
| 90 | * function here than what even the RNDRSS register provides |
| 91 | * (the output of a pseudo RNG freshly seeded by a TRNG). |
| 92 | */ |
| 93 | if (smccc_trng_available) { |
| 94 | struct arm_smccc_res res; |
| 95 | |
| 96 | max_longs = min_t(size_t, 3, max_longs); |
| 97 | arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res); |
| 98 | if ((int)res.a0 >= 0) { |
| 99 | switch (max_longs) { |
| 100 | case 3: |
| 101 | *v++ = res.a1; |
| 102 | fallthrough; |
| 103 | case 2: |
| 104 | *v++ = res.a2; |
| 105 | fallthrough; |
| 106 | case 1: |
| 107 | *v++ = res.a3; |
| 108 | break; |
| 109 | } |
| 110 | return max_longs; |
| 111 | } |
| 112 | } |
| 113 | |
| 114 | /* |
| 115 | * RNDRRS is not backed by an entropy source but by a DRBG that is |
| 116 | * reseeded after each invocation. This is not a 100% fit but good |
| 117 | * enough to implement this API if no other entropy source exists. |
| 118 | */ |
| 119 | if (__cpu_has_rng() && __arm64_rndrrs(v)) |
| 120 | return 1; |
| 121 | |
| 122 | return 0; |
| 123 | } |
| 124 | |
| 125 | static inline bool __init __early_cpu_has_rndr(void) |
| 126 | { |
| 127 | /* Open code as we run prior to the first call to cpufeature. */ |
| 128 | unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1); |
| 129 | return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf; |
| 130 | } |
| 131 | |
| 132 | #endif /* _ASM_ARCHRANDOM_H */ |
| 133 |
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