Index: head/lib/libc/gen/getentropy.c
===================================================================
--- head/lib/libc/gen/getentropy.c	(revision 338083)
+++ head/lib/libc/gen/getentropy.c	(revision 338084)
@@ -1,128 +1,149 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
  * Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/random.h>
 #include <sys/sysctl.h>
 
 #include <errno.h>
+#include <stdbool.h>
 #include <stdlib.h>
 
 #include "libc_private.h"
 
+/* First __FreeBSD_version bump after introduction of getrandom(2) (r331279) */
+#define GETRANDOM_FIRST 1200061
+
 extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t);
 
 static size_t
 arnd_sysctl(u_char *buf, size_t size)
 {
 	int mib[2];
 	size_t len, done;
 
 	mib[0] = CTL_KERN;
 	mib[1] = KERN_ARND;
 	done = 0;
 
 	do {
 		len = size;
 		if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
 			return (done);
 		done += len;
 		buf += len;
 		size -= len;
 	} while (size > 0);
 
 	return (done);
 }
 
 /*
  * If a newer libc is accidentally installed on an older kernel, provide high
  * quality random data anyway.  The sysctl interface is not as fast and does
  * not block by itself, but is provided by even very old kernels.
  */
 static int
 getentropy_fallback(void *buf, size_t buflen)
 {
 	/*
 	 * oldp (buf) == NULL has a special meaning for sysctl that results in
 	 * no EFAULT.  For compatibility with the kernel getrandom(2), detect
 	 * this case and return the appropriate error.
 	 */
 	if (buf == NULL && buflen > 0) {
 		errno = EFAULT;
 		return (-1);
 	}
 	if (arnd_sysctl(buf, buflen) != buflen) {
 		if (errno == EFAULT)
 			return (-1);
 		/*
 		 * This cannot happen.  _arc4_sysctl() spins until the random
 		 * device is seeded and then repeatedly reads until the full
 		 * request is satisfied.  The only way for this to return a zero
 		 * byte or short read is if sysctl(2) on the kern.arandom MIB
 		 * fails.  In this case, exceping the user-provided-a-bogus-
 		 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir).
 		 */
 		abort();
 	}
 	return (0);
 }
 
 int
 getentropy(void *buf, size_t buflen)
 {
 	ssize_t rd;
+	bool have_getrandom;
 
 	if (buflen > 256) {
 		errno = EIO;
 		return (-1);
 	}
 
+	have_getrandom = (__getosreldate() >= GETRANDOM_FIRST);
+
 	while (buflen > 0) {
-		rd = getrandom(buf, buflen, 0);
-		if (rd == -1) {
-			if (errno == EINTR)
-				continue;
-			else if (errno == ENOSYS || errno == ECAPMODE)
-				return (getentropy_fallback(buf, buflen));
-			else
-				return (-1);
+		if (have_getrandom) {
+			rd = getrandom(buf, buflen, 0);
+			if (rd == -1) {
+				switch (errno) {
+				case ECAPMODE:
+					/*
+					 * Kernel >= r331280 and < r337999
+					 * will return ECAPMODE when the
+					 * caller is already in capability
+					 * mode, fallback to traditional
+					 * method in this case.
+					 */
+					have_getrandom = false;
+					continue;
+				case EINTR:
+					continue;
+				default:
+					return (-1);
+				}
+			}
+		} else {
+			return (getentropy_fallback(buf, buflen));
 		}
 
 		/* This cannot happen. */
 		if (rd == 0)
 			abort();
 
 		buf = (char *)buf + rd;
 		buflen -= rd;
 	}
 
 	return (0);
 }