cprng_fast.c revision 1.18
1 /* $NetBSD: cprng_fast.c,v 1.18 2022/09/01 18:32:25 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 1.18 2022/09/01 18:32:25 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 #include <sys/pserialize.h> 45 46 #include <crypto/chacha/chacha.h> 47 48 #define CPRNG_FAST_SEED_BYTES CHACHA_STREAM_KEYBYTES 50 51 struct cprng_fast { 52 /* 128-bit vector unit generates 256 bytes at once */ 53 uint8_t buf[256]; 54 uint8_t key[CPRNG_FAST_SEED_BYTES]; 55 uint8_t nonce[CHACHA_STREAM_NONCEBYTES]; 56 unsigned i; 57 struct evcnt *reseed_evcnt; 58 unsigned epoch; 59 }; 60 61 static void cprng_fast_init_cpu(void *, void *, struct cpu_info *); 62 static void cprng_fast_reseed(struct cprng_fast *); 63 64 static void cprng_fast_seed(struct cprng_fast *, const void *); 65 static void cprng_fast_buf(struct cprng_fast *, void *, unsigned); 66 67 static void cprng_fast_buf_short(void *, size_t); 68 static void cprng_fast_buf_long(void *, size_t); 69 70 static percpu_t *cprng_fast_percpu __read_mostly; 71 72 void 73 cprng_fast_init(void) 74 { 75 76 cprng_fast_percpu = percpu_create(sizeof(struct cprng_fast), 77 cprng_fast_init_cpu, NULL, NULL); 78 } 79 80 static void 81 cprng_fast_init_cpu(void *p, void *arg __unused, struct cpu_info *ci) 82 { 83 struct cprng_fast *const cprng = p; 84 85 cprng->epoch = 0; 86 87 cprng->reseed_evcnt = kmem_alloc(sizeof(*cprng->reseed_evcnt), 88 KM_SLEEP); 89 evcnt_attach_dynamic(cprng->reseed_evcnt, EVCNT_TYPE_MISC, NULL, 90 ci->ci_cpuname, "cprng_fast reseed"); 91 } 92 93 static int 95 cprng_fast_get(struct cprng_fast **cprngp) 96 { 97 struct cprng_fast *cprng; 98 int s; 99 100 KASSERT(!cpu_intr_p()); 101 KASSERT(pserialize_not_in_read_section()); 102 103 *cprngp = cprng = percpu_getref(cprng_fast_percpu); 104 s = splsoftserial(); 105 106 if (__predict_false(cprng->epoch != entropy_epoch())) { 107 splx(s); 108 cprng_fast_reseed(cprng); 109 s = splsoftserial(); 110 } 111 112 return s; 113 } 114 115 static void 116 cprng_fast_put(struct cprng_fast *cprng, int s) 117 { 118 119 KASSERT((cprng == percpu_getref(cprng_fast_percpu)) && 120 (percpu_putref(cprng_fast_percpu), true)); 121 splx(s); 122 percpu_putref(cprng_fast_percpu); 123 } 124 125 static void 126 cprng_fast_reseed(struct cprng_fast *cprng) 127 { 128 unsigned epoch = entropy_epoch(); 129 uint8_t seed[CPRNG_FAST_SEED_BYTES]; 130 int s; 131 132 cprng_strong(kern_cprng, seed, sizeof(seed), 0); 133 134 s = splsoftserial(); 135 cprng_fast_seed(cprng, seed); 136 cprng->epoch = epoch; 137 cprng->reseed_evcnt->ev_count++; 138 splx(s); 139 140 explicit_memset(seed, 0, sizeof(seed)); 141 } 142 143 /* CPRNG algorithm */ 145 146 static void 147 cprng_fast_seed(struct cprng_fast *cprng, const void *seed) 148 { 149 150 (void)memset(cprng->buf, 0, sizeof cprng->buf); 151 (void)memcpy(cprng->key, seed, sizeof cprng->key); 152 (void)memset(cprng->nonce, 0, sizeof cprng->nonce); 153 cprng->i = sizeof cprng->buf; 154 } 155 156 static void 157 cprng_fast_buf(struct cprng_fast *cprng, void *buf, unsigned len) 158 { 159 uint8_t *p = buf; 160 unsigned n = len, n0; 161 162 KASSERT(cprng->i <= sizeof(cprng->buf)); 163 KASSERT(len <= sizeof(cprng->buf)); 164 165 n0 = MIN(n, sizeof(cprng->buf) - cprng->i); 166 memcpy(p, &cprng->buf[cprng->i], n0); 167 if ((n -= n0) == 0) { 168 cprng->i += n0; 169 KASSERT(cprng->i <= sizeof(cprng->buf)); 170 return; 171 } 172 p += n0; 173 le64enc(cprng->nonce, 1 + le64dec(cprng->nonce)); 174 chacha_stream(cprng->buf, sizeof(cprng->buf), 0, cprng->nonce, 175 cprng->key, 8); 176 memcpy(p, cprng->buf, n); 177 cprng->i = n; 178 } 179 180 /* Public API */ 182 183 static void 184 cprng_fast_buf_short(void *buf, size_t len) 185 { 186 struct cprng_fast *cprng; 187 int s; 188 189 KASSERT(len <= sizeof(cprng->buf)); 190 191 s = cprng_fast_get(&cprng); 192 cprng_fast_buf(cprng, buf, len); 193 cprng_fast_put(cprng, s); 194 } 195 196 static void 197 cprng_fast_buf_long(void *buf, size_t len) 198 { 199 uint8_t seed[CHACHA_STREAM_KEYBYTES]; 200 uint8_t nonce[CHACHA_STREAM_NONCEBYTES] = {0}; 201 202 CTASSERT(sizeof(seed) <= sizeof(((struct cprng_fast *)0)->buf)); 203 204 #if SIZE_MAX >= 0x3fffffffff 205 /* >=256 GB is not reasonable */ 206 KASSERT(len <= 0x3fffffffff); 207 #endif 208 209 cprng_fast_buf_short(seed, sizeof seed); 210 chacha_stream(buf, len, 0, nonce, seed, 8); 211 212 (void)explicit_memset(seed, 0, sizeof seed); 213 } 214 215 uint32_t 216 cprng_fast32(void) 217 { 218 uint32_t v; 219 220 cprng_fast_buf_short(&v, sizeof v); 221 222 return v; 223 } 224 225 uint64_t 226 cprng_fast64(void) 227 { 228 uint64_t v; 229 230 cprng_fast_buf_short(&v, sizeof v); 231 232 return v; 233 } 234 235 size_t 236 cprng_fast(void *buf, size_t len) 237 { 238 239 /* 240 * We don't want to hog the CPU, so we use the short version, 241 * to generate output without preemption, only if we can do it 242 * with at most one ChaCha call. 243 */ 244 if (len <= sizeof(((struct cprng_fast *)0)->buf)) 245 cprng_fast_buf_short(buf, len); 246 else 247 cprng_fast_buf_long(buf, len); 248 249 return len; /* hysterical raisins */ 250 } 251
Indexes created Wed Oct 01 07:09:59 GMT 2025