1 /*- 2 * Copyright (c) 2013, 2025, David E. O'Brien <deo@NUXI.org> 3 * Copyright (c) 2013 The FreeBSD Foundation 4 * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Portions of this software were developed by Konstantin Belousov 8 * under sponsorship from the FreeBSD Foundation. 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 * in this position and unchanged. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 21 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 22 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 23 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 24 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 25 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 29 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 * 31 */ 32 33 #include <sys/param.h> 34 #include <sys/kernel.h> 35 #include <sys/conf.h> 36 #include <sys/lock.h> 37 #include <sys/malloc.h> 38 #include <sys/module.h> 39 #include <sys/random.h> 40 #include <sys/sysctl.h> 41 #include <sys/systm.h> 42 43 #include <machine/md_var.h> 44 #include <machine/specialreg.h> 45 46 #include <dev/random/randomdev.h> 47 48 #define RETRY_COUNT 10 49 50 static u_int random_ivy_read(void *, u_int); 51 52 static const struct random_source random_ivy = { 53 .rs_ident = "Intel Secure Key RNG", 54 .rs_source = RANDOM_PURE_RDRAND, 55 .rs_read = random_ivy_read 56 }; 57 58 static bool acquire_independent_seed_samples = false; 59 60 static bool 61 x86_rdrand_store(u_long *buf) 62 { 63 u_long rndval, seed_iterations, i; 64 int retry; 65 66 /* Per [1], "§ 5.2.6 Generating Seeds from RDRAND," 67 * machines lacking RDSEED will guarantee RDRAND is reseeded every 8kB 68 * of generated output. 69 * 70 * [1]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide#inpage-nav-6-8 71 */ 72 if (acquire_independent_seed_samples) 73 seed_iterations = 8 * 1024 / sizeof(*buf); 74 else 75 seed_iterations = 1; 76 77 for (i = 0; i < seed_iterations; i++) { 78 retry = RETRY_COUNT; 79 __asm __volatile( 80 "1:\n\t" 81 "rdrand %1\n\t" /* read randomness into rndval */ 82 "jc 2f\n\t" /* CF is set on success, exit retry loop */ 83 "dec %0\n\t" /* otherwise, retry-- */ 84 "jne 1b\n\t" /* and loop if retries are not exhausted */ 85 "2:" 86 : "+r" (retry), "=r" (rndval) : : "cc"); 87 if (retry == 0) 88 return (false); 89 } 90 *buf = rndval; 91 return (true); 92 } 93 94 /* It is required that buf length is a multiple of sizeof(u_long). */ 95 static u_int 96 random_ivy_read(void *buf, u_int c) 97 { 98 u_long *b, rndval; 99 u_int count; 100 101 KASSERT(c % sizeof(*b) == 0, ("partial read %d", c)); 102 b = buf; 103 for (count = c; count > 0; count -= sizeof(*b)) { 104 if (!x86_rdrand_store(&rndval)) 105 break; 106 *b++ = rndval; 107 } 108 return (c - count); 109 } 110 111 static int 112 rdrand_modevent(module_t mod, int type, void *unused) 113 { 114 struct sysctl_ctx_list ctx; 115 struct sysctl_oid *o; 116 bool has_rdrand, has_rdseed; 117 int error = 0; 118 119 has_rdrand = (cpu_feature2 & CPUID2_RDRAND); 120 has_rdseed = (cpu_stdext_feature & CPUID_STDEXT_RDSEED); 121 122 switch (type) { 123 case MOD_LOAD: 124 if (has_rdrand && !has_rdseed) { 125 sysctl_ctx_init(&ctx); 126 o = SYSCTL_ADD_NODE(&ctx, SYSCTL_STATIC_CHILDREN(_kern_random), 127 OID_AUTO, "rdrand", CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 128 "rdrand (ivy) entropy source"); 129 SYSCTL_ADD_BOOL(&ctx, SYSCTL_CHILDREN(o), OID_AUTO, 130 "rdrand_independent_seed", CTLFLAG_RDTUN, 131 &acquire_independent_seed_samples, 0, 132 "If non-zero, use more expensive and slow, but safer, seeded samples " 133 "where RDSEED is not present."); 134 random_source_register(&random_ivy); 135 printf("random: fast provider: \"%s\"\n", random_ivy.rs_ident); 136 } 137 break; 138 139 case MOD_UNLOAD: 140 if (has_rdrand && !has_rdseed) 141 random_source_deregister(&random_ivy); 142 break; 143 144 case MOD_SHUTDOWN: 145 break; 146 147 default: 148 error = EOPNOTSUPP; 149 break; 150 151 } 152 153 return (error); 154 } 155 156 static moduledata_t rdrand_mod = { 157 "rdrand", 158 rdrand_modevent, 159 0 160 }; 161 162 DECLARE_MODULE(rdrand, rdrand_mod, SI_SUB_RANDOM, SI_ORDER_FOURTH); 163 MODULE_VERSION(rdrand, 1); 164 MODULE_DEPEND(rdrand, random_harvestq, 1, 1, 1); 165