util: Add qemu_guest_getrandom and associated routines

This routine is intended to produce high-quality random numbers to the
guest.  Normally, such numbers are crypto quality from the host, but a
command-line option can force the use of a fully deterministic sequence
for use while debugging.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/include/qemu/guest-random.h b/include/qemu/guest-random.h
new file mode 100644
index 0000000000..09ff9c2236
--- /dev/null
+++ b/include/qemu/guest-random.h
@@ -0,0 +1,68 @@
+/*
+ * QEMU guest-visible random functions
+ *
+ * Copyright 2019 Linaro, Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#ifndef QEMU_GUEST_RANDOM_H
+#define QEMU_GUEST_RANDOM_H
+
+/**
+ * qemu_guest_random_seed_main(const char *optarg, Error **errp)
+ * @optarg: a non-NULL pointer to a C string
+ * @errp: an error indicator
+ *
+ * The @optarg value is that which accompanies the -seed argument.
+ * This forces qemu_guest_getrandom into deterministic mode.
+ *
+ * Returns 0 on success, < 0 on failure while setting *errp.
+ */
+int qemu_guest_random_seed_main(const char *optarg, Error **errp);
+
+/**
+ * qemu_guest_random_seed_thread_part1(void)
+ *
+ * If qemu_getrandom is in deterministic mode, returns an
+ * independent seed for the new thread.  Otherwise returns 0.
+ */
+uint64_t qemu_guest_random_seed_thread_part1(void);
+
+/**
+ * qemu_guest_random_seed_thread_part2(uint64_t seed)
+ * @seed: a value for the new thread.
+ *
+ * If qemu_guest_getrandom is in deterministic mode, this stores an
+ * independent seed for the new thread.  Otherwise a no-op.
+ */
+void qemu_guest_random_seed_thread_part2(uint64_t seed);
+
+/**
+ * qemu_guest_getrandom(void *buf, size_t len, Error **errp)
+ * @buf: a buffer of bytes to be written
+ * @len: the number of bytes in @buf
+ * @errp: an error indicator
+ *
+ * Fills len bytes in buf with random data.  This should only be used
+ * for data presented to the guest.  Host-side crypto services should
+ * use qcrypto_random_bytes.
+ *
+ * Returns 0 on success, < 0 on failure while setting *errp.
+ */
+int qemu_guest_getrandom(void *buf, size_t len, Error **errp);
+
+/**
+ * qemu_guest_getrandom_nofail(void *buf, size_t len)
+ * @buf: a buffer of bytes to be written
+ * @len: the number of bytes in @buf
+ *
+ * Like qemu_guest_getrandom, but will assert for failure.
+ * Use this when there is no reasonable recovery.
+ */
+void qemu_guest_getrandom_nofail(void *buf, size_t len);
+
+#endif /* QEMU_GUEST_RANDOM_H */