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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