1 /* $OpenBSD: getentropy_osx.c,v 1.12 2018/11/20 08:04:28 deraadt Exp $ */
4 * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
5 * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
19 * Emulation of getentropy(2) as documented at:
20 * http://man.openbsd.org/getentropy.2
23 #include <TargetConditionals.h>
24 #include <sys/types.h>
25 #include <sys/param.h>
26 #include <sys/ioctl.h>
27 #include <sys/resource.h>
28 #include <sys/syscall.h>
29 #include <sys/sysctl.h>
30 #include <sys/statvfs.h>
31 #include <sys/socket.h>
32 #include <sys/mount.h>
46 #include <mach/mach_time.h>
47 #include <mach/mach_host.h>
48 #include <mach/host_info.h>
50 #include <sys/socketvar.h>
51 #include <sys/vmmeter.h>
53 #include <netinet/in.h>
54 #include <netinet/tcp.h>
56 #include <netinet/udp.h>
57 #include <netinet/ip_var.h>
58 #include <netinet/tcp_var.h>
59 #include <netinet/udp_var.h>
61 #include <CommonCrypto/CommonDigest.h>
62 #define SHA512_Update(a, b, c) (CC_SHA512_Update((a), (b), (c)))
63 #define SHA512_Init(xxx) (CC_SHA512_Init((xxx)))
64 #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy)))
65 #define SHA512_CTX CC_SHA512_CTX
66 #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH
69 #define min(a, b) (((a) < (b)) ? (a) : (b))
79 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
80 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
81 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
83 int getentropy(void *buf, size_t len);
85 static int getentropy_urandom(void *buf, size_t len);
86 static int getentropy_fallback(void *buf, size_t len);
89 getentropy(void *buf, size_t len)
99 * Try to get entropy with /dev/urandom
101 * This can fail if the process is inside a chroot or if file
102 * descriptors are exhausted.
104 ret = getentropy_urandom(buf, len);
109 * Entropy collection via /dev/urandom and sysctl have failed.
111 * No other API exists for collecting entropy, and we have
112 * no failsafe way to get it on OSX that is not sensitive
113 * to resource exhaustion.
115 * We have very few options:
116 * - Even syslog_r is unsafe to call at this low level, so
117 * there is no way to alert the user or program.
118 * - Cannot call abort() because some systems have unsafe
120 * - Could raise(SIGKILL) resulting in silent program termination.
121 * - Return EIO, to hint that arc4random's stir function
122 * should raise(SIGKILL)
123 * - Do the best under the circumstances....
125 * This code path exists to bring light to the issue that OSX
126 * does not provide a failsafe API for entropy collection.
128 * We hope this demonstrates that OSX should consider
129 * providing a new failsafe API which works in a chroot or
130 * when file descriptors are exhausted.
132 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
133 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
136 ret = getentropy_fallback(buf, len);
145 getentropy_urandom(void *buf, size_t len)
150 int save_errno = errno;
161 fd = open("/dev/urandom", flags, 0);
168 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
171 /* Lightly verify that the device node looks sane */
172 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
176 for (i = 0; i < len; ) {
177 size_t wanted = len - i;
178 ssize_t ret = read(fd, (char *)buf + i, wanted);
181 if (errno == EAGAIN || errno == EINTR)
190 return (0); /* satisfied */
197 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS };
198 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS };
199 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS };
201 static int kmib[] = { CTL_KERN, KERN_USRSTACK };
202 static int hwmib[] = { CTL_HW, HW_USERMEM };
205 getentropy_fallback(void *buf, size_t len)
207 uint8_t results[SHA512_DIGEST_LENGTH];
208 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
216 static pid_t lastpid;
221 struct tcpstat tcpstat;
222 struct udpstat udpstat;
223 struct ipstat ipstat;
230 if (lastpid == pid) {
238 for (i = 0; i < len; ) {
241 for (j = 0; j < repeat; j++) {
242 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
244 cnt += (int)tv.tv_sec;
245 cnt += (int)tv.tv_usec;
248 mach_time = mach_absolute_time();
252 HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]),
253 &addr, &ii, NULL, 0) == -1, addr);
256 HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]),
257 &idata, &ii, NULL, 0) == -1, idata);
260 ii = sizeof(tcpstat);
261 HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]),
262 &tcpstat, &ii, NULL, 0) == -1, tcpstat);
264 ii = sizeof(udpstat);
265 HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]),
266 &udpstat, &ii, NULL, 0) == -1, udpstat);
269 HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]),
270 &ipstat, &ii, NULL, 0) == -1, ipstat);
273 HX((pid = getpid()) == -1, pid);
274 HX((pid = getsid(pid)) == -1, pid);
275 HX((pid = getppid()) == -1, pid);
276 HX((pid = getpgid(0)) == -1, pid);
277 HX((e = getpriority(0, 0)) == -1, e);
282 (void) nanosleep(&ts, NULL);
285 HX(sigpending(&sigset) == -1, sigset);
286 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
289 HF(getentropy); /* an addr in this library */
290 HF(printf); /* an addr in libc */
292 HD(p); /* an addr on stack */
294 HD(p); /* the addr of errno */
297 struct sockaddr_storage ss;
298 struct statvfs stvfs;
305 * Prime-sized mappings encourage fragmentation;
306 * thus exposing some address entropy.
312 { 17, MAP_FAILED }, { 3, MAP_FAILED },
313 { 11, MAP_FAILED }, { 2, MAP_FAILED },
314 { 5, MAP_FAILED }, { 3, MAP_FAILED },
315 { 7, MAP_FAILED }, { 1, MAP_FAILED },
316 { 57, MAP_FAILED }, { 3, MAP_FAILED },
317 { 131, MAP_FAILED }, { 1, MAP_FAILED },
320 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
321 HX(mm[m].p = mmap(NULL,
323 PROT_READ|PROT_WRITE,
324 MAP_PRIVATE|MAP_ANON, -1,
326 if (mm[m].p != MAP_FAILED) {
329 /* Touch some memory... */
332 (mm[m].npg * pgs - 1);
334 cnt += (int)((long)(mm[m].p)
338 /* Check cnts and times... */
339 mach_time = mach_absolute_time();
341 cnt += (int)mach_time;
343 HX((e = getrusage(RUSAGE_SELF,
346 cnt += (int)ru.ru_utime.tv_sec;
347 cnt += (int)ru.ru_utime.tv_usec;
351 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
352 if (mm[m].p != MAP_FAILED)
353 munmap(mm[m].p, mm[m].npg * pgs);
354 mm[m].p = MAP_FAILED;
357 HX(stat(".", &st) == -1, st);
358 HX(statvfs(".", &stvfs) == -1, stvfs);
359 HX(statfs(".", &stfs) == -1, stfs);
361 HX(stat("/", &st) == -1, st);
362 HX(statvfs("/", &stvfs) == -1, stvfs);
363 HX(statfs("/", &stfs) == -1, stfs);
365 HX((e = fstat(0, &st)) == -1, st);
367 if (S_ISREG(st.st_mode) ||
368 S_ISFIFO(st.st_mode) ||
369 S_ISSOCK(st.st_mode)) {
370 HX(fstatvfs(0, &stvfs) == -1,
372 HX(fstatfs(0, &stfs) == -1,
374 HX((off = lseek(0, (off_t)0,
375 SEEK_CUR)) < 0, off);
377 if (S_ISCHR(st.st_mode)) {
378 HX(tcgetattr(0, &tios) == -1,
380 } else if (S_ISSOCK(st.st_mode)) {
381 memset(&ss, 0, sizeof ss);
384 (void *)&ss, &ssl) == -1,
389 HX((e = getrusage(RUSAGE_CHILDREN,
392 cnt += (int)ru.ru_utime.tv_sec;
393 cnt += (int)ru.ru_utime.tv_usec;
396 /* Subsequent hashes absorb previous result */
400 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
402 cnt += (int)tv.tv_sec;
403 cnt += (int)tv.tv_usec;
409 SHA512_Final(results, &ctx);
410 memcpy((char *)buf + i, results, min(sizeof(results), len - i));
411 i += min(sizeof(results), len - i);
413 explicit_bzero(&ctx, sizeof ctx);
414 explicit_bzero(results, sizeof results);
416 return (0); /* satisfied */