1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_ARCHRANDOM_H
3 #define _ASM_ARCHRANDOM_H
4 
5 #ifdef CONFIG_ARCH_RANDOM
6 
7 #include <linux/arm-smccc.h>
8 #include <linux/bug.h>
9 #include <linux/kernel.h>
10 #include <asm/cpufeature.h>
11 
12 #define ARM_SMCCC_TRNG_MIN_VERSION	0x10000UL
13 
14 extern bool smccc_trng_available;
15 
16 static inline bool __init smccc_probe_trng(void)
17 {
18 	struct arm_smccc_res res;
19 
20 	arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res);
21 	if ((s32)res.a0 < 0)
22 		return false;
23 
24 	return res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION;
25 }
26 
27 static inline bool __arm64_rndr(unsigned long *v)
28 {
29 	bool ok;
30 
31 	/*
32 	 * Reads of RNDR set PSTATE.NZCV to 0b0000 on success,
33 	 * and set PSTATE.NZCV to 0b0100 otherwise.
34 	 */
35 	asm volatile(
36 		__mrs_s("%0", SYS_RNDR_EL0) "\n"
37 	"	cset %w1, ne\n"
38 	: "=r" (*v), "=r" (ok)
39 	:
40 	: "cc");
41 
42 	return ok;
43 }
44 
45 static inline bool __arm64_rndrrs(unsigned long *v)
46 {
47 	bool ok;
48 
49 	/*
50 	 * Reads of RNDRRS set PSTATE.NZCV to 0b0000 on success,
51 	 * and set PSTATE.NZCV to 0b0100 otherwise.
52 	 */
53 	asm volatile(
54 		__mrs_s("%0", SYS_RNDRRS_EL0) "\n"
55 	"	cset %w1, ne\n"
56 	: "=r" (*v), "=r" (ok)
57 	:
58 	: "cc");
59 
60 	return ok;
61 }
62 
63 static inline bool __must_check arch_get_random_long(unsigned long *v)
64 {
65 	/*
66 	 * Only support the generic interface after we have detected
67 	 * the system wide capability, avoiding complexity with the
68 	 * cpufeature code and with potential scheduling between CPUs
69 	 * with and without the feature.
70 	 */
71 	if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v))
72 		return true;
73 	return false;
74 }
75 
76 static inline bool __must_check arch_get_random_int(unsigned int *v)
77 {
78 	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
79 		unsigned long val;
80 
81 		if (__arm64_rndr(&val)) {
82 			*v = val;
83 			return true;
84 		}
85 	}
86 	return false;
87 }
88 
89 static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
90 {
91 	struct arm_smccc_res res;
92 
93 	/*
94 	 * We prefer the SMCCC call, since its semantics (return actual
95 	 * hardware backed entropy) is closer to the idea behind this
96 	 * function here than what even the RNDRSS register provides
97 	 * (the output of a pseudo RNG freshly seeded by a TRNG).
98 	 */
99 	if (smccc_trng_available) {
100 		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
101 		if ((int)res.a0 >= 0) {
102 			*v = res.a3;
103 			return true;
104 		}
105 	}
106 
107 	/*
108 	 * RNDRRS is not backed by an entropy source but by a DRBG that is
109 	 * reseeded after each invocation. This is not a 100% fit but good
110 	 * enough to implement this API if no other entropy source exists.
111 	 */
112 	if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndrrs(v))
113 		return true;
114 
115 	return false;
116 }
117 
118 static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
119 {
120 	struct arm_smccc_res res;
121 	unsigned long val;
122 
123 	if (smccc_trng_available) {
124 		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 32, &res);
125 		if ((int)res.a0 >= 0) {
126 			*v = res.a3 & GENMASK(31, 0);
127 			return true;
128 		}
129 	}
130 
131 	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
132 		if (__arm64_rndrrs(&val)) {
133 			*v = val;
134 			return true;
135 		}
136 	}
137 
138 	return false;
139 }
140 
141 static inline bool __init __early_cpu_has_rndr(void)
142 {
143 	/* Open code as we run prior to the first call to cpufeature. */
144 	unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
145 	return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
146 }
147 
148 static inline bool __init __must_check
149 arch_get_random_seed_long_early(unsigned long *v)
150 {
151 	WARN_ON(system_state != SYSTEM_BOOTING);
152 
153 	if (smccc_trng_available) {
154 		struct arm_smccc_res res;
155 
156 		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
157 		if ((int)res.a0 >= 0) {
158 			*v = res.a3;
159 			return true;
160 		}
161 	}
162 
163 	if (__early_cpu_has_rndr() && __arm64_rndr(v))
164 		return true;
165 
166 	return false;
167 }
168 #define arch_get_random_seed_long_early arch_get_random_seed_long_early
169 
170 #else /* !CONFIG_ARCH_RANDOM */
171 
172 static inline bool __init smccc_probe_trng(void)
173 {
174 	return false;
175 }
176 
177 #endif /* CONFIG_ARCH_RANDOM */
178 #endif /* _ASM_ARCHRANDOM_H */
179