cprng_fast.c revision 1.17
1 /* $NetBSD: cprng_fast.c,v 1.17 2022/06/01 15:44:37 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2014 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Taylor R. Campbell. 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 #include <sys/cdefs.h> 33 __KERNEL_RCSID(0, "$NetBSD: cprng_fast.c,v 1.17 2022/06/01 15:44:37 riastradh Exp $"); 34 35 #include <sys/types.h> 36 #include <sys/param.h> 37 #include <sys/bitops.h> 38 #include <sys/cprng.h> 39 #include <sys/cpu.h> 40 #include <sys/entropy.h> 41 #include <sys/evcnt.h> 42 #include <sys/kmem.h> 43 #include <sys/percpu.h> 44 45 #include <crypto/chacha/chacha.h> 46 47 #define CPRNG_FAST_SEED_BYTES CHACHA_STREAM_KEYBYTES 49 50 struct cprng_fast { 51 /* 128-bit vector unit generates 256 bytes at once */ 52 uint8_t buf[256]; 53 uint8_t key[CPRNG_FAST_SEED_BYTES]; 54 uint8_t nonce[CHACHA_STREAM_NONCEBYTES]; 55 unsigned i; 56 struct evcnt *reseed_evcnt; 57 unsigned epoch; 58 }; 59 60 static void cprng_fast_init_cpu(void *, void *, struct cpu_info *); 61 static void cprng_fast_reseed(struct cprng_fast *); 62 63 static void cprng_fast_seed(struct cprng_fast *, const void *); 64 static void cprng_fast_buf(struct cprng_fast *, void *, unsigned); 65 66 static void cprng_fast_buf_short(void *, size_t); 67 static void cprng_fast_buf_long(void *, size_t); 68 69 static percpu_t *cprng_fast_percpu __read_mostly; 70 71 void 72 cprng_fast_init(void) 73 { 74 75 cprng_fast_percpu = percpu_create(sizeof(struct cprng_fast), 76 cprng_fast_init_cpu, NULL, NULL); 77 } 78 79 static void 80 cprng_fast_init_cpu(void *p, void *arg __unused, struct cpu_info *ci) 81 { 82 struct cprng_fast *const cprng = p; 83 84 cprng->epoch = 0; 85 86 cprng->reseed_evcnt = kmem_alloc(sizeof(*cprng->reseed_evcnt), 87 KM_SLEEP); 88 evcnt_attach_dynamic(cprng->reseed_evcnt, EVCNT_TYPE_MISC, NULL, 89 ci->ci_cpuname, "cprng_fast reseed"); 90 } 91 92 static int 94 cprng_fast_get(struct cprng_fast **cprngp) 95 { 96 struct cprng_fast *cprng; 97 int s; 98 99 KASSERT(!cpu_intr_p()); 100 101 *cprngp = cprng = percpu_getref(cprng_fast_percpu); 102 s = splsoftserial(); 103 104 if (__predict_false(cprng->epoch != entropy_epoch())) { 105 splx(s); 106 cprng_fast_reseed(cprng); 107 s = splsoftserial(); 108 } 109 110 return s; 111 } 112 113 static void 114 cprng_fast_put(struct cprng_fast *cprng, int s) 115 { 116 117 KASSERT((cprng == percpu_getref(cprng_fast_percpu)) && 118 (percpu_putref(cprng_fast_percpu), true)); 119 splx(s); 120 percpu_putref(cprng_fast_percpu); 121 } 122 123 static void 124 cprng_fast_reseed(struct cprng_fast *cprng) 125 { 126 unsigned epoch = entropy_epoch(); 127 uint8_t seed[CPRNG_FAST_SEED_BYTES]; 128 int s; 129 130 cprng_strong(kern_cprng, seed, sizeof(seed), 0); 131 132 s = splsoftserial(); 133 cprng_fast_seed(cprng, seed); 134 cprng->epoch = epoch; 135 cprng->reseed_evcnt->ev_count++; 136 splx(s); 137 138 explicit_memset(seed, 0, sizeof(seed)); 139 } 140 141 /* CPRNG algorithm */ 143 144 static void 145 cprng_fast_seed(struct cprng_fast *cprng, const void *seed) 146 { 147 148 (void)memset(cprng->buf, 0, sizeof cprng->buf); 149 (void)memcpy(cprng->key, seed, sizeof cprng->key); 150 (void)memset(cprng->nonce, 0, sizeof cprng->nonce); 151 cprng->i = sizeof cprng->buf; 152 } 153 154 static void 155 cprng_fast_buf(struct cprng_fast *cprng, void *buf, unsigned len) 156 { 157 uint8_t *p = buf; 158 unsigned n = len, n0; 159 160 KASSERT(cprng->i <= sizeof(cprng->buf)); 161 KASSERT(len <= sizeof(cprng->buf)); 162 163 n0 = MIN(n, sizeof(cprng->buf) - cprng->i); 164 memcpy(p, &cprng->buf[cprng->i], n0); 165 if ((n -= n0) == 0) { 166 cprng->i += n0; 167 KASSERT(cprng->i <= sizeof(cprng->buf)); 168 return; 169 } 170 p += n0; 171 le64enc(cprng->nonce, 1 + le64dec(cprng->nonce)); 172 chacha_stream(cprng->buf, sizeof(cprng->buf), 0, cprng->nonce, 173 cprng->key, 8); 174 memcpy(p, cprng->buf, n); 175 cprng->i = n; 176 } 177 178 /* Public API */ 180 181 static void 182 cprng_fast_buf_short(void *buf, size_t len) 183 { 184 struct cprng_fast *cprng; 185 int s; 186 187 KASSERT(len <= sizeof(cprng->buf)); 188 189 s = cprng_fast_get(&cprng); 190 cprng_fast_buf(cprng, buf, len); 191 cprng_fast_put(cprng, s); 192 } 193 194 static void 195 cprng_fast_buf_long(void *buf, size_t len) 196 { 197 uint8_t seed[CHACHA_STREAM_KEYBYTES]; 198 uint8_t nonce[CHACHA_STREAM_NONCEBYTES] = {0}; 199 200 CTASSERT(sizeof(seed) <= sizeof(((struct cprng_fast *)0)->buf)); 201 202 #if SIZE_MAX >= 0x3fffffffff 203 /* >=256 GB is not reasonable */ 204 KASSERT(len <= 0x3fffffffff); 205 #endif 206 207 cprng_fast_buf_short(seed, sizeof seed); 208 chacha_stream(buf, len, 0, nonce, seed, 8); 209 210 (void)explicit_memset(seed, 0, sizeof seed); 211 } 212 213 uint32_t 214 cprng_fast32(void) 215 { 216 uint32_t v; 217 218 cprng_fast_buf_short(&v, sizeof v); 219 220 return v; 221 } 222 223 uint64_t 224 cprng_fast64(void) 225 { 226 uint64_t v; 227 228 cprng_fast_buf_short(&v, sizeof v); 229 230 return v; 231 } 232 233 size_t 234 cprng_fast(void *buf, size_t len) 235 { 236 237 /* 238 * We don't want to hog the CPU, so we use the short version, 239 * to generate output without preemption, only if we can do it 240 * with at most one ChaCha call. 241 */ 242 if (len <= sizeof(((struct cprng_fast *)0)->buf)) 243 cprng_fast_buf_short(buf, len); 244 else 245 cprng_fast_buf_long(buf, len); 246 247 return len; /* hysterical raisins */ 248 } 249
Indexes created Wed Oct 01 07:09:59 GMT 2025