fuzz: add fuzzer skeleton

tests/fuzz/fuzz.c serves as the entry point for the virtual-device
fuzzer. Namely, libfuzzer invokes the LLVMFuzzerInitialize and
LLVMFuzzerTestOneInput functions, both of which are defined in this
file. This change adds a "FuzzTarget" struct, along with the
fuzz_add_target function, which should be used to define new fuzz
targets.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200220041118.23264-13-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 95 insertions, 0 deletions

diff --git a/tests/qtest/fuzz/fuzz.h b/tests/qtest/fuzz/fuzz.h
new file mode 100644
index 0000000000..03901d414e
--- /dev/null
+++ b/tests/qtest/fuzz/fuzz.h
@@ -0,0 +1,95 @@
+/*
+ * fuzzing driver
+ *
+ * Copyright Red Hat Inc., 2019
+ *
+ * Authors:
+ *  Alexander Bulekov   <alxndr@bu.edu>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef FUZZER_H_
+#define FUZZER_H_
+
+#include "qemu/osdep.h"
+#include "qemu/units.h"
+#include "qapi/error.h"
+
+#include "tests/qtest/libqtest.h"
+
+/**
+ * A libfuzzer fuzzing target
+ *
+ * The QEMU fuzzing binary is built with all available targets, each
+ * with a unique @name that can be specified on the command-line to
+ * select which target should run.
+ *
+ * A target must implement ->fuzz() to process a random input.  If QEMU
+ * crashes in ->fuzz() then libfuzzer will record a failure.
+ *
+ * Fuzzing targets are registered with fuzz_add_target():
+ *
+ *   static const FuzzTarget fuzz_target = {
+ *       .name = "my-device-fifo",
+ *       .description = "Fuzz the FIFO buffer registers of my-device",
+ *       ...
+ *   };
+ *
+ *   static void register_fuzz_target(void)
+ *   {
+ *       fuzz_add_target(&fuzz_target);
+ *   }
+ *   fuzz_target_init(register_fuzz_target);
+ */
+typedef struct FuzzTarget {
+    const char *name;         /* target identifier (passed to --fuzz-target=)*/
+    const char *description;  /* help text */
+
+
+    /*
+     * returns the arg-list that is passed to qemu/softmmu init()
+     * Cannot be NULL
+     */
+    const char* (*get_init_cmdline)(struct FuzzTarget *);
+
+    /*
+     * will run once, prior to running qemu/softmmu init.
+     * eg: set up shared-memory for communication with the child-process
+     * Can be NULL
+     */
+    void(*pre_vm_init)(void);
+
+    /*
+     * will run once, after QEMU has been initialized, prior to the fuzz-loop.
+     * eg: detect the memory map
+     * Can be NULL
+     */
+    void(*pre_fuzz)(QTestState *);
+
+    /*
+     * accepts and executes an input from libfuzzer. this is repeatedly
+     * executed during the fuzzing loop. Its should handle setup, input
+     * execution and cleanup.
+     * Cannot be NULL
+     */
+    void(*fuzz)(QTestState *, const unsigned char *, size_t);
+
+} FuzzTarget;
+
+void flush_events(QTestState *);
+void reboot(QTestState *);
+
+/*
+ * makes a copy of *target and adds it to the target-list.
+ * i.e. fine to set up target on the caller's stack
+ */
+void fuzz_add_target(const FuzzTarget *target);
+
+int LLVMFuzzerTestOneInput(const unsigned char *Data, size_t Size);
+int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp);
+
+#endif
+