1 files changed, 114 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..a8fbb706
--- /dev/null
+++ b/util/libreboot-utils/lib/rand.c
@@ -0,0 +1,114 @@
+/* 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>
+
+#include <errno.h>
+#if !((defined(__OpenBSD__) && (OpenBSD) >= 201) || \
+    defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__APPLE__))
+#include <fcntl.h> /* if not arc4random: /dev/urandom */
+#endif
+#include <limits.h>
+#include <stddef.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+#include "../include/common.h"
+
+/* Random numbers
+ */
+
+/* when calling this: save errno
+ * first, then set errno to zero.
+ * on error, this function will
+ * set errno and possibly return
+ *
+ * rlong also preserves errno
+ * and leaves it unchanged on
+ * success, so if you do it
+ * right, you can detect error.
+ * this is because it uses
+ * /dev/urandom which can err.
+ * ditto getrandom (EINTR),
+ * theoretically.
+ */
+
+/* for the linux version: we use only the
+ * syscall, because we cannot trust /dev/urandom
+ * to be as robust, and some libc implementations
+ * may default to /dev/urandom under fault conditions.
+ *
+ * for general high reliability, we must abort on
+ * failure. in practise, it will likely never fail.
+ * the arc4random call on bsd never returns error.
+ */
+
+size_t
+rlong(void)
+{
+	size_t rval;
+	int saved_errno = errno;
+	errno = 0;
+
+#if (defined(__OpenBSD__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__APPLE__) || \
+    defined(__DragonFly__))
+
+	arc4random_buf(&rval, sizeof(size_t));
+	goto out;
+
+#elif defined(__linux__)
+
+	size_t off = 0;
+	size_t len = sizeof(rval);
+	ssize_t rc;
+
+retry_rand:
+	rc = (ssize_t)syscall(SYS_getrandom,
+	    (char *)&rval + off, len - off, 0);
+
+	if (rc < 0) {
+		if (errno == EINTR || errno == EAGAIN) {
+			usleep(100);
+			goto retry_rand;
+		}
+
+		goto err; /* possibly unsupported by kernel */
+	}
+
+	if ((off += (size_t)rc) < len)
+		goto retry_rand;
+
+	goto out;
+err:
+	/*
+	 * getrandom can return with error, butt arc4random
+	 * doesn't. generally, getrandom will be reliably,
+	 * but we of course have to maintain parity with
+	 * BSD. So a rand failure is to be interpreted as
+	 * a major systems failure, and we act accordingly.
+	 */
+	err_no_cleanup(1, ECANCELED,
+	    "Randomisation failure, possibly unsupported in your kernel.");
+	exit(EXIT_FAILURE);
+
+#else
+#error Unsupported operating system (possibly unsecure randomisation)
+#endif
+
+out:
+	errno = saved_errno;
+	return rval;
+}
+#endif