diff --git a/libc/bionic/getentropy.cpp b/libc/bionic/getentropy.cpp
new file mode 100644
index 0000000..2c6e417
--- /dev/null
+++ b/libc/bionic/getentropy.cpp
@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * 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 COPYRIGHT HOLDERS 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
+ * COPYRIGHT OWNER 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 <errno.h>
+#include <fcntl.h>
+#include <sys/random.h>
+#include <unistd.h>
+
+static int getentropy_urandom(void* buffer, size_t buffer_size, int saved_errno) {
+  int fd = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY | O_NOFOLLOW | O_CLOEXEC, 0));
+  if (fd == -1) return -1;
+
+  size_t collected = 0;
+  while (collected < buffer_size) {
+    ssize_t count = TEMP_FAILURE_RETRY(read(fd, static_cast<char*>(buffer) + collected,
+                                            buffer_size - collected));
+    if (count == -1) {
+      close(fd);
+      return -1;
+    }
+    collected += count;
+  }
+
+  close(fd);
+  errno = saved_errno;
+  return 0;
+}
+
+int getentropy(void* buffer, size_t buffer_size) {
+  if (buffer_size > 256) {
+    errno = EIO;
+    return -1;
+  }
+
+  int saved_errno = errno;
+
+  size_t collected = 0;
+  while (collected < buffer_size) {
+    long count = TEMP_FAILURE_RETRY(getrandom(static_cast<char*>(buffer) + collected,
+                                              buffer_size - collected, GRND_NONBLOCK));
+    if (count == -1) {
+      // EAGAIN: there isn't enough entropy right now.
+      // ENOSYS/EINVAL: getrandom(2) or GRND_NONBLOCK isn't supported.
+      // EFAULT: `buffer` is invalid.
+      // Try /dev/urandom regardless because it can't hurt,
+      // and we don't need to optimize the EFAULT case.
+      // See http://b/33059407 and http://b/67015565.
+      return getentropy_urandom(buffer, buffer_size, saved_errno);
+    }
+    collected += count;
+  }
+
+  errno = saved_errno;
+  return 0;
+}