1 | /* $NetBSD: cpu_rng.c,v 1.5 2016/02/29 00:17:54 riastradh Exp $ */ |
2 | |
3 | /*- |
4 | * Copyright (c) 2015 The NetBSD Foundation, Inc. |
5 | * All rights reserved. |
6 | * |
7 | * This code is derived from software contributed to The NetBSD Foundation |
8 | * by Thor Lancelot Simon. |
9 | * |
10 | * Redistribution and use in source and binary forms, with or without |
11 | * modification, are permitted provided that the following conditions |
12 | * are met: |
13 | * 1. Redistributions of source code must retain the above copyright |
14 | * notice, this list of conditions and the following disclaimer. |
15 | * 2. Redistributions in binary form must reproduce the above copyright |
16 | * notice, this list of conditions and the following disclaimer in the |
17 | * documentation and/or other materials provided with the distribution. |
18 | * |
19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
29 | * POSSIBILITY OF SUCH DAMAGE. |
30 | */ |
31 | |
32 | /* |
33 | * The VIA RNG code in this file is inspired by Jason Wright and |
34 | * Theo de Raadt's OpenBSD version but has been rewritten in light of |
35 | * comments from Henric Jungheim on the tech@openbsd.org mailing list. |
36 | */ |
37 | |
38 | #include <sys/param.h> |
39 | #include <sys/systm.h> |
40 | #include <sys/cpu.h> |
41 | |
42 | #include <x86/specialreg.h> |
43 | |
44 | #include <machine/cpufunc.h> |
45 | #include <machine/cpuvar.h> |
46 | #include <machine/cpu_rng.h> |
47 | |
48 | static enum { |
49 | CPU_RNG_NONE = 0, |
50 | CPU_RNG_RDRAND, |
51 | CPU_RNG_RDSEED, |
52 | CPU_RNG_VIA |
53 | } cpu_rng_mode __read_mostly = CPU_RNG_NONE; |
54 | |
55 | bool |
56 | cpu_rng_init(void) |
57 | { |
58 | |
59 | if (cpu_feature[5] & CPUID_SEF_RDSEED) { |
60 | cpu_rng_mode = CPU_RNG_RDSEED; |
61 | aprint_normal("cpu_rng: RDSEED\n" ); |
62 | return true; |
63 | } else if (cpu_feature[1] & CPUID2_RDRAND) { |
64 | cpu_rng_mode = CPU_RNG_RDRAND; |
65 | aprint_normal("cpu_rng: RDRAND\n" ); |
66 | return true; |
67 | } else if (cpu_feature[4] & CPUID_VIA_HAS_RNG) { |
68 | cpu_rng_mode = CPU_RNG_VIA; |
69 | aprint_normal("cpu_rng: VIA\n" ); |
70 | return true; |
71 | } |
72 | return false; |
73 | } |
74 | |
75 | static size_t |
76 | cpu_rng_rdrand(cpu_rng_t *out) |
77 | { |
78 | uint8_t rndsts; |
79 | |
80 | #ifdef __i386__ |
81 | uint32_t lo, hi; |
82 | |
83 | __asm __volatile("rdrand %0; setc %1" : "=r" (lo), "=qm" (rndsts)); |
84 | if (rndsts != 1) |
85 | return 0; |
86 | __asm __volatile("rdrand %0; setc %1" : "=r" (hi), "=qm" (rndsts)); |
87 | |
88 | *out = (uint64_t)lo | ((uint64_t)hi << 32); |
89 | explicit_memset(&lo, 0, sizeof(lo)); |
90 | explicit_memset(&hi, 0, sizeof(hi)); |
91 | if (rndsts != 1) |
92 | return sizeof(lo) * NBBY; |
93 | #else |
94 | __asm __volatile("rdrand %0; setc %1" : "=r" (*out), "=qm" (rndsts)); |
95 | if (rndsts != 1) |
96 | return 0; |
97 | #endif |
98 | return sizeof(*out) * NBBY; |
99 | } |
100 | |
101 | static size_t |
102 | cpu_rng_rdseed(cpu_rng_t *out) |
103 | { |
104 | uint8_t rndsts; |
105 | |
106 | #ifdef __i386__ |
107 | uint32_t lo, hi; |
108 | |
109 | __asm __volatile("rdseed %0; setc %1" : "=r" (lo), "=qm" (rndsts)); |
110 | if (rndsts != 1) |
111 | goto exhausted; |
112 | __asm __volatile("rdseed %0; setc %1" : "=r" (hi), "=qm" (rndsts)); |
113 | if (rndsts != 1) |
114 | goto exhausted; |
115 | |
116 | *out = (uint64_t)lo | ((uint64_t)hi << 32); |
117 | explicit_memset(&lo, 0, sizeof(lo)); |
118 | explicit_memset(&hi, 0, sizeof(hi)); |
119 | #else |
120 | __asm __volatile("rdseed %0; setc %1" : "=r" (*out), "=qm" (rndsts)); |
121 | #endif |
122 | if (rndsts != 1) |
123 | goto exhausted; |
124 | |
125 | return sizeof(*out) * NBBY; |
126 | |
127 | /* |
128 | * Userspace could have exhausted RDSEED, but the |
129 | * CPU-internal generator feeding RDRAND is guaranteed |
130 | * to be seeded even in this case. |
131 | */ |
132 | exhausted: |
133 | return cpu_rng_rdrand(out); |
134 | } |
135 | |
136 | static size_t |
137 | cpu_rng_via(cpu_rng_t *out) |
138 | { |
139 | uint32_t creg0, rndsts; |
140 | |
141 | /* |
142 | * Sadly, we have to monkey with the coprocessor enable and fault |
143 | * registers, which are really for the FPU, in order to read |
144 | * from the RNG. |
145 | * |
146 | * Don't remove CR0_TS from the call below -- comments in the Linux |
147 | * driver indicate that the xstorerng instruction can generate |
148 | * spurious DNA faults though no FPU or SIMD state is changed |
149 | * even if such a fault is generated. |
150 | * |
151 | * XXX can this really happen if we don't use "rep xstorrng"? |
152 | * |
153 | */ |
154 | kpreempt_disable(); |
155 | x86_disable_intr(); |
156 | creg0 = rcr0(); |
157 | lcr0(creg0 & ~(CR0_EM|CR0_TS)); /* Permit access to SIMD/FPU path */ |
158 | /* |
159 | * The VIA RNG has an output queue of 8-byte values. Read one. |
160 | * This is atomic, so if the FPU were already enabled, we could skip |
161 | * all the preemption and interrupt frobbing. If we had bread, |
162 | * we could have a ham sandwich, if we had any ham. |
163 | */ |
164 | __asm __volatile("xstorerng" |
165 | : "=a" (rndsts), "+D" (out) : "d" (0) : "memory" ); |
166 | /* Put CR0 back how it was */ |
167 | lcr0(creg0); |
168 | x86_enable_intr(); |
169 | kpreempt_enable(); |
170 | |
171 | /* |
172 | * The Cryptography Research paper on the VIA RNG estimates |
173 | * 0.75 bits of entropy per output bit and advises users to |
174 | * be "even more conservative". |
175 | */ |
176 | return rndsts & 0xf ? 0 : sizeof(cpu_rng_t) * NBBY / 2; |
177 | } |
178 | |
179 | size_t |
180 | cpu_rng(cpu_rng_t *out) |
181 | { |
182 | |
183 | switch (cpu_rng_mode) { |
184 | case CPU_RNG_NONE: |
185 | return 0; |
186 | case CPU_RNG_RDSEED: |
187 | return cpu_rng_rdseed(out); |
188 | case CPU_RNG_RDRAND: |
189 | return cpu_rng_rdrand(out); |
190 | case CPU_RNG_VIA: |
191 | return cpu_rng_via(out); |
192 | default: |
193 | panic("cpu_rng: unknown mode %d" , (int)cpu_rng_mode); |
194 | } |
195 | } |
196 | |