sandbox: Add libfuzzer integration

Add an implementation of LLVMFuzzerTestOneInput() that starts the
sandbox on a secondary thread and exposes a function to synchronize the
generation of fuzzing inputs with their consumption by the sandbox.

Signed-off-by: Andrew Scull <ascull@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/fuzzing_engine.h

@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2022 Google, Inc.
+ * Written by Andrew Scull <ascull@google.com>
+ */
+
+#ifndef __ASM_FUZZING_ENGINE_H
+#define __ASM_FUZZING_ENGINE_H
+
+/** Function to get fuzzing engine input data. */
+/**
+ * sandbox_fuzzing_engine_get_input() - get an input from the sandbox fuzzing
+ * 					engine
+ *
+ * The function will return a pointer to the input data and the size of the
+ * data pointed to. The pointer will remain valid until the next invocation of
+ * this function.
+ *
+ * @data:	output pointer to input data
+ * @size	output size of input data
+ * Return:	0 if OK, -ve on error
+ */
+int sandbox_fuzzing_engine_get_input(const uint8_t **data, size_t *size);
+
+#endif /* __ASM_FUZZING_ENGINE_H */