[PATCH v4 15/20] fuzz: add fuzzer skeleton

["Oleinik, Alexander" <alxndr@bu.edu>]

From: Alexander Oleinik <alxndr@bu.edu>

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 Oleinik <alxndr@bu.edu>
---
 tests/fuzz/Makefile.include |   4 +-
 tests/fuzz/fuzz.c           | 177 ++++++++++++++++++++++++++++++++++++
 tests/fuzz/fuzz.h           |  66 ++++++++++++++
 3 files changed, 245 insertions(+), 2 deletions(-)
 create mode 100644 tests/fuzz/fuzz.c
 create mode 100644 tests/fuzz/fuzz.h

diff --git a/tests/fuzz/Makefile.include b/tests/fuzz/Makefile.include
index 324e6c1433..b415b056b0 100644
--- a/tests/fuzz/Makefile.include
+++ b/tests/fuzz/Makefile.include
@@ -1,4 +1,4 @@
-# QEMU_PROG_FUZZ=qemu-fuzz-$(TARGET_NAME)$(EXESUF)
+QEMU_PROG_FUZZ=qemu-fuzz-$(TARGET_NAME)$(EXESUF)
 fuzz-obj-y = $(libqos-obj-y)
 fuzz-obj-y += tests/libqtest.o
-
+fuzz-obj-y += tests/fuzz/fuzz.o
diff --git a/tests/fuzz/fuzz.c b/tests/fuzz/fuzz.c
new file mode 100644
index 0000000000..0e38f81c48
--- /dev/null
+++ b/tests/fuzz/fuzz.c
@@ -0,0 +1,177 @@
+/*
+ * 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.
+ *
+ */
+
+#include "qemu/osdep.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <wordexp.h>
+
+
+#include "tests/libqtest.h"
+#include "sysemu/qtest.h"
+#include "fuzz.h"
+#include "tests/libqos/qgraph.h"
+#include "sysemu/runstate.h"
+#include "sysemu/sysemu.h"
+#include "qemu/main-loop.h"
+
+typedef struct FuzzTargetState {
+        FuzzTarget *target;
+        QSLIST_ENTRY(FuzzTargetState) target_list;
+} FuzzTargetState;
+
+typedef QSLIST_HEAD(, FuzzTargetState) FuzzTargetList;
+
+static const char *fuzz_arch = TARGET_NAME;
+
+static FuzzTargetList *fuzz_target_list;
+static FuzzTarget *fuzz_target;
+static QTestState *fuzz_qts;
+
+
+
+void flush_events(QTestState *s)
+{
+    int i = 10;
+    while (g_main_context_pending(NULL) && i-- > 0) {
+        main_loop_wait(false);
+    }
+}
+
+static QTestState *qtest_setup(void)
+{
+    qtest_server_set_tx_handler(&qtest_client_inproc_recv, NULL);
+    return qtest_inproc_init(false, fuzz_arch, &qtest_server_inproc_recv);
+}
+
+void fuzz_add_target(FuzzTarget *target)
+{
+    FuzzTargetState *tmp;
+    FuzzTargetState *target_state;
+    if (!fuzz_target_list) {
+        fuzz_target_list = g_new0(FuzzTargetList, 1);
+    }
+
+    QSLIST_FOREACH(tmp, fuzz_target_list, target_list) {
+        if (g_strcmp0(tmp->target->name, target->name) == 0) {
+            fprintf(stderr, "Error: Fuzz target name %s already in use\n",
+                    target->name);
+            abort();
+        }
+    }
+    target_state = g_new0(FuzzTargetState, 1);
+    target_state->target = g_new0(FuzzTarget, 1);
+    *(target_state->target) = *target;
+    QSLIST_INSERT_HEAD(fuzz_target_list, target_state, target_list);
+}
+
+
+
+static void usage(char *path)
+{
+    printf("Usage: %s --fuzz-target=FUZZ_TARGET [LIBFUZZER ARGUMENTS]\n", path);
+    printf("where FUZZ_TARGET is one of:\n");
+    FuzzTargetState *tmp;
+    if (!fuzz_target_list) {
+        fprintf(stderr, "Fuzz target list not initialized\n");
+        abort();
+    }
+    QSLIST_FOREACH(tmp, fuzz_target_list, target_list) {
+        printf(" %s  : %s\n", tmp->target->name,
+                tmp->target->description);
+    }
+    exit(0);
+}
+
+static FuzzTarget *fuzz_get_target(char* name)
+{
+    FuzzTargetState *tmp;
+    if (!fuzz_target_list) {
+        fprintf(stderr, "Fuzz target list not initialized\n");
+        abort();
+    }
+
+    QSLIST_FOREACH(tmp, fuzz_target_list, target_list) {
+        if (strcmp(tmp->target->name, name) == 0) {
+            return tmp->target;
+        }
+    }
+    return NULL;
+}
+
+
+/* Executed for each fuzzing-input */
+int LLVMFuzzerTestOneInput(const unsigned char *Data, size_t Size)
+{
+    if (fuzz_target->fuzz) {
+        fuzz_target->fuzz(fuzz_qts, Data, Size);
+    }
+    return 0;
+}
+
+/* Executed once, prior to fuzzing */
+int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp)
+{
+
+    char *target_name;
+
+    /* Initialize qgraph and modules */
+    qos_graph_init();
+    module_call_init(MODULE_INIT_FUZZ_TARGET);
+    module_call_init(MODULE_INIT_QOM);
+    module_call_init(MODULE_INIT_LIBQOS);
+
+    if (*argc <= 1) {
+        usage(**argv);
+    }
+
+    /* Identify the fuzz target */
+    target_name = (*argv)[1];
+    if (!strstr(target_name, "--fuzz-target=")) {
+        usage(**argv);
+    }
+
+    target_name += strlen("--fuzz-target=");
+
+    fuzz_target = fuzz_get_target(target_name);
+    if (!fuzz_target) {
+        usage(**argv);
+    }
+
+    fuzz_qts = qtest_setup();
+
+    if (!fuzz_target) {
+        fprintf(stderr, "Error: Fuzz fuzz_target name %s not found\n",
+                target_name);
+        usage(**argv);
+    }
+
+    if (fuzz_target->pre_vm_init) {
+        fuzz_target->pre_vm_init();
+    }
+
+    /* Run QEMU's softmmu main with the fuzz-target dependent arguments */
+    char *init_cmdline = fuzz_target->get_init_cmdline(fuzz_target);
+
+    wordexp_t result;
+    wordexp(init_cmdline, &result, 0);
+
+    qemu_init(result.we_wordc, result.we_wordv, NULL);
+
+    if (fuzz_target->pre_fuzz) {
+        fuzz_target->pre_fuzz(fuzz_qts);
+    }
+
+    return 0;
+}
diff --git a/tests/fuzz/fuzz.h b/tests/fuzz/fuzz.h
new file mode 100644
index 0000000000..b569b622d7
--- /dev/null
+++ b/tests/fuzz/fuzz.h
@@ -0,0 +1,66 @@
+/*
+ * 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 "exec/memory.h"
+#include "tests/libqtest.h"
+
+
+typedef struct FuzzTarget {
+    const char *name;         /* command-line option(FUZZ_TARGET) for the target */
+    const char *description;  /* help text */
+
+
+    /* returns the arg-list that is passed to qemu/softmmu init() */
+    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
+     */
+    void(*pre_vm_init)(void);
+
+    /*
+     * will run once, prior to to the fuzz-loop.
+     * eg: detect the memory map
+     */
+    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
+     */
+    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(FuzzTarget *target);
+
+int LLVMFuzzerTestOneInput(const unsigned char *Data, size_t Size);
+int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp);
+
+#endif
+
-- 
2.23.0