| 1 | /* $NetBSD: kern_rndsink.c,v 1.17 2016/05/21 15:33:40 riastradh Exp $ */ |
| 2 | |
| 3 | /*- |
| 4 | * Copyright (c) 2013 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: kern_rndsink.c,v 1.17 2016/05/21 15:33:40 riastradh Exp $" ); |
| 34 | |
| 35 | #include <sys/param.h> |
| 36 | #include <sys/types.h> |
| 37 | #include <sys/condvar.h> |
| 38 | #include <sys/kmem.h> |
| 39 | #include <sys/mutex.h> |
| 40 | #include <sys/queue.h> |
| 41 | #include <sys/rndsink.h> |
| 42 | |
| 43 | #include <dev/rnd_private.h> |
| 44 | |
| 45 | enum rsink_state { |
| 46 | RNDSINK_IDLE, /* no callback in progress */ |
| 47 | RNDSINK_QUEUED, /* queued for callback */ |
| 48 | RNDSINK_IN_FLIGHT, /* callback called */ |
| 49 | RNDSINK_REQUEUED, /* queued again before callback done */ |
| 50 | RNDSINK_DEAD, /* destroyed */ |
| 51 | }; |
| 52 | |
| 53 | struct rndsink { |
| 54 | /* Callback state. */ |
| 55 | enum rsink_state rsink_state; |
| 56 | |
| 57 | /* Entry on the queue of rndsinks, iff in the RNDSINK_QUEUED state. */ |
| 58 | TAILQ_ENTRY(rndsink) rsink_entry; |
| 59 | |
| 60 | /* rndsink_create parameters. */ |
| 61 | unsigned int rsink_bytes; |
| 62 | rndsink_callback_t *rsink_callback; |
| 63 | void *rsink_arg; |
| 64 | }; |
| 65 | |
| 66 | static struct { |
| 67 | kmutex_t lock; |
| 68 | kcondvar_t cv; |
| 69 | TAILQ_HEAD(, rndsink) q; |
| 70 | } rndsinks __cacheline_aligned; |
| 71 | |
| 72 | void |
| 73 | rndsinks_init(void) |
| 74 | { |
| 75 | |
| 76 | /* |
| 77 | * This mutex must be at an ipl as high as the highest ipl of |
| 78 | * anyone who wants to call rndsink_request. |
| 79 | * |
| 80 | * XXX Call this IPL_RND, perhaps. |
| 81 | */ |
| 82 | mutex_init(&rndsinks.lock, MUTEX_DEFAULT, IPL_VM); |
| 83 | cv_init(&rndsinks.cv, "rndsink" ); |
| 84 | TAILQ_INIT(&rndsinks.q); |
| 85 | } |
| 86 | |
| 87 | void |
| 88 | rndsinks_distribute(void) |
| 89 | { |
| 90 | uint8_t buffer[RNDSINK_MAX_BYTES]; |
| 91 | struct rndsink *rndsink; |
| 92 | |
| 93 | explicit_memset(buffer, 0, sizeof(buffer)); /* paranoia */ |
| 94 | |
| 95 | mutex_spin_enter(&rndsinks.lock); |
| 96 | while ((rndsink = TAILQ_FIRST(&rndsinks.q)) != NULL) { |
| 97 | KASSERT(rndsink->rsink_state == RNDSINK_QUEUED); |
| 98 | |
| 99 | /* Bail if we can't get some entropy for this rndsink. */ |
| 100 | if (!rnd_tryextract(buffer, rndsink->rsink_bytes)) |
| 101 | break; |
| 102 | |
| 103 | /* |
| 104 | * Got some entropy. Take the sink off the queue and |
| 105 | * feed the entropy to the callback, with rndsinks_lock |
| 106 | * dropped. While running the callback, lock out |
| 107 | * rndsink_destroy by marking the sink in flight. |
| 108 | */ |
| 109 | TAILQ_REMOVE(&rndsinks.q, rndsink, rsink_entry); |
| 110 | rndsink->rsink_state = RNDSINK_IN_FLIGHT; |
| 111 | mutex_spin_exit(&rndsinks.lock); |
| 112 | |
| 113 | (*rndsink->rsink_callback)(rndsink->rsink_arg, buffer, |
| 114 | rndsink->rsink_bytes); |
| 115 | explicit_memset(buffer, 0, rndsink->rsink_bytes); |
| 116 | |
| 117 | mutex_spin_enter(&rndsinks.lock); |
| 118 | |
| 119 | /* |
| 120 | * If, while the callback was running, anyone requested |
| 121 | * it be queued up again, do so now. Otherwise, idle. |
| 122 | * Either way, it is now safe to destroy, so wake the |
| 123 | * pending rndsink_destroy, if there is one. |
| 124 | */ |
| 125 | if (rndsink->rsink_state == RNDSINK_REQUEUED) { |
| 126 | TAILQ_INSERT_TAIL(&rndsinks.q, rndsink, rsink_entry); |
| 127 | rndsink->rsink_state = RNDSINK_QUEUED; |
| 128 | } else { |
| 129 | KASSERT(rndsink->rsink_state == RNDSINK_IN_FLIGHT); |
| 130 | rndsink->rsink_state = RNDSINK_IDLE; |
| 131 | } |
| 132 | cv_broadcast(&rndsinks.cv); |
| 133 | } |
| 134 | mutex_spin_exit(&rndsinks.lock); |
| 135 | |
| 136 | explicit_memset(buffer, 0, sizeof(buffer)); /* paranoia */ |
| 137 | } |
| 138 | |
| 139 | static void |
| 140 | rndsinks_enqueue(struct rndsink *rndsink) |
| 141 | { |
| 142 | |
| 143 | KASSERT(mutex_owned(&rndsinks.lock)); |
| 144 | |
| 145 | /* Kick on-demand entropy sources. */ |
| 146 | rnd_getmore(rndsink->rsink_bytes); |
| 147 | |
| 148 | /* Ensure this rndsink is on the queue. */ |
| 149 | switch (rndsink->rsink_state) { |
| 150 | case RNDSINK_IDLE: |
| 151 | /* Not on the queue and nobody is handling it. */ |
| 152 | TAILQ_INSERT_TAIL(&rndsinks.q, rndsink, rsink_entry); |
| 153 | rndsink->rsink_state = RNDSINK_QUEUED; |
| 154 | break; |
| 155 | |
| 156 | case RNDSINK_QUEUED: |
| 157 | /* Already on the queue. */ |
| 158 | break; |
| 159 | |
| 160 | case RNDSINK_IN_FLIGHT: |
| 161 | /* Someone is handling it. Ask to queue it up again. */ |
| 162 | rndsink->rsink_state = RNDSINK_REQUEUED; |
| 163 | break; |
| 164 | |
| 165 | case RNDSINK_REQUEUED: |
| 166 | /* Already asked to queue it up again. */ |
| 167 | break; |
| 168 | |
| 169 | case RNDSINK_DEAD: |
| 170 | panic("requesting entropy from dead rndsink: %p" , rndsink); |
| 171 | |
| 172 | default: |
| 173 | panic("rndsink %p in unknown state: %d" , rndsink, |
| 174 | (int)rndsink->rsink_state); |
| 175 | } |
| 176 | } |
| 177 | |
| 178 | struct rndsink * |
| 179 | rndsink_create(size_t bytes, rndsink_callback_t *callback, void *arg) |
| 180 | { |
| 181 | struct rndsink *const rndsink = kmem_alloc(sizeof(*rndsink), KM_SLEEP); |
| 182 | |
| 183 | KASSERT(bytes <= RNDSINK_MAX_BYTES); |
| 184 | |
| 185 | rndsink->rsink_state = RNDSINK_IDLE; |
| 186 | rndsink->rsink_bytes = bytes; |
| 187 | rndsink->rsink_callback = callback; |
| 188 | rndsink->rsink_arg = arg; |
| 189 | |
| 190 | return rndsink; |
| 191 | } |
| 192 | |
| 193 | void |
| 194 | rndsink_destroy(struct rndsink *rndsink) |
| 195 | { |
| 196 | |
| 197 | /* |
| 198 | * Make sure the rndsink is off the queue, and if it's already |
| 199 | * in flight, wait for the callback to complete. |
| 200 | */ |
| 201 | mutex_spin_enter(&rndsinks.lock); |
| 202 | while (rndsink->rsink_state != RNDSINK_IDLE) { |
| 203 | switch (rndsink->rsink_state) { |
| 204 | case RNDSINK_QUEUED: |
| 205 | TAILQ_REMOVE(&rndsinks.q, rndsink, rsink_entry); |
| 206 | rndsink->rsink_state = RNDSINK_IDLE; |
| 207 | break; |
| 208 | |
| 209 | case RNDSINK_IN_FLIGHT: |
| 210 | case RNDSINK_REQUEUED: |
| 211 | cv_wait(&rndsinks.cv, &rndsinks.lock); |
| 212 | break; |
| 213 | |
| 214 | case RNDSINK_DEAD: |
| 215 | panic("destroying dead rndsink: %p" , rndsink); |
| 216 | |
| 217 | default: |
| 218 | panic("rndsink %p in unknown state: %d" , rndsink, |
| 219 | (int)rndsink->rsink_state); |
| 220 | } |
| 221 | } |
| 222 | rndsink->rsink_state = RNDSINK_DEAD; |
| 223 | mutex_spin_exit(&rndsinks.lock); |
| 224 | |
| 225 | kmem_free(rndsink, sizeof(*rndsink)); |
| 226 | } |
| 227 | |
| 228 | void |
| 229 | rndsink_schedule(struct rndsink *rndsink) |
| 230 | { |
| 231 | |
| 232 | /* Optimistically check without the lock whether we're queued. */ |
| 233 | if ((rndsink->rsink_state != RNDSINK_QUEUED) && |
| 234 | (rndsink->rsink_state != RNDSINK_REQUEUED)) { |
| 235 | mutex_spin_enter(&rndsinks.lock); |
| 236 | rndsinks_enqueue(rndsink); |
| 237 | mutex_spin_exit(&rndsinks.lock); |
| 238 | } |
| 239 | } |
| 240 | |
| 241 | bool |
| 242 | rndsink_request(struct rndsink *rndsink, void *buffer, size_t bytes) |
| 243 | { |
| 244 | |
| 245 | KASSERT(bytes == rndsink->rsink_bytes); |
| 246 | |
| 247 | mutex_spin_enter(&rndsinks.lock); |
| 248 | const bool full_entropy = rnd_extract(buffer, bytes); |
| 249 | if (!full_entropy) |
| 250 | rndsinks_enqueue(rndsink); |
| 251 | mutex_spin_exit(&rndsinks.lock); |
| 252 | |
| 253 | return full_entropy; |
| 254 | } |
| 255 | |