1 files changed, 135 insertions, 0 deletions
diff --git a/util/libreboot-utils/lib/rand.c b/util/libreboot-utils/lib/rand.c
new file mode 100644
index 00000000..7b53b6a4
--- /dev/null
+++ b/util/libreboot-utils/lib/rand.c
@@ -0,0 +1,135 @@
+/* SPDX-License-Identifier: MIT
+ * Copyright (c) 2026 Leah Rowe <leah@libreboot.org>
+ *
+ * Random number generation
+ */
+
+#ifndef RAND_H
+#define RAND_H
+
+#ifdef __OpenBSD__
+#include <sys/param.h>
+#endif
+#include <sys/types.h>
+
+#ifndef USE_URANDOM
+#define USE_URANDOM 0
+#endif
+
+#include <errno.h>
+#if defined(USE_URANDOM) && \
+    ((USE_URANDOM) > 0)
+#include <fcntl.h> /* if not arc4random: /dev/urandom */
+#endif
+
+#include <fcntl.h>
+#include <limits.h>
+#include <stddef.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "../include/common.h"
+
+/* Regarding Linux getrandom/urandom:
+ *
+ * For maximum security guarantee, we *only*
+ * use getrandom via syscall, or /dev/urandom;
+ * use of urandom is ill advised. This is why
+ * we use the syscall, in case the libc version
+ * of getrandom() might defer to /dev/urandom
+ *
+ * We *abort* on error, for both /dev/urandom
+ * and getrandom(), because the BSD arc4random
+ * never returns with error; therefore, for the
+ * most parity in terms of behaviour, we abort,
+ * because otherwise the function would have two
+ * return modes: always successful (BSD), or only
+ * sometimes (Linux). The BSD arc4random could
+ * theoretically abort; it is extremely unlikely
+ * there, and just so on Linux, hence this design.
+ *
+ * This is important, because cryptographic code
+ * for example must not rely on weak randomness.
+ * We must therefore treat broken randomness as
+ * though the world is broken, and burn accordingly.
+ *
+ * Similarly, any invalid input (NULL, zero bytes
+ * requested) are treated as fatal errors; again,
+ * cryptographic code must be reliable. If your
+ * code erroneously requested zero bytes, you might
+ * then end up with a non-randomised buffer, where
+ * you likely intended otherwise.
+ *
+ * In other words: call rset() correctly, or your
+ * program dies, and rset will behave correctly,
+ * or your program dies.
+ */
+
+void
+rset(void *buf, size_t n)
+{
+	int saved_errno = errno;
+
+	if (if_err(buf == NULL, EFAULT))
+		goto err;
+
+	if (n == 0)
+		err_no_cleanup(0, EPERM,
+		  "rset: zero-byte length request");
+
+#if (defined(__OpenBSD__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__APPLE__) || \
+    defined(__DragonFly__)) && !(defined(USE_URANDOM) && \
+    ((USE_URANDOM) > 0))
+
+	arc4random_buf(buf, n);
+	goto out;
+#else
+	size_t off = 0;
+	ssize_t rc = 0;
+
+#if defined(USE_URANDOM) && \
+    ((USE_URANDOM) > 0)
+	int fd = -1;
+
+	if ((fd = open("/dev/urandom", O_RDONLY)) < 0)
+		goto err;
+retry_rand:
+	if ((rc = read(fd, (unsigned char *)buf + off, n - off)) < 0) {
+#elif defined(__linux__)
+retry_rand:
+	if ((rc = (ssize_t)syscall(SYS_getrandom,
+	    (unsigned char *)buf + off, n - off, 0)) < 0) {
+#else
+#error Unsupported operating system (possibly unsecure randomisation)
+#endif
+		if (errno == EINTR ||
+		    errno == EAGAIN)
+			goto retry_rand;
+
+		goto err; /* possibly unsupported by kernel */
+	}
+
+	if (rc == 0)
+		goto err; /* prevent infinite loop on fatal err */
+
+	if ((off += (size_t)rc) < n)
+		goto retry_rand;
+
+#if defined(USE_URANDOM) && \
+    ((USE_URANDOM) > 0)
+	close_no_err(&fd);
+#endif
+	goto out;
+#endif
+out:
+	errno = saved_errno;
+	return;
+err:
+	err_no_cleanup(0, ECANCELED,
+	    "Randomisation failure, possibly unsupported in your kernel");
+	exit(EXIT_FAILURE);
+}
+#endif