| 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 | |