libfuzzer driver + llvm_mode compilation optimization

1 files changed, 281 insertions, 0 deletions

diff --git a/examples/aflpp_driver/aflpp_driver.cpp b/examples/aflpp_driver/aflpp_driver.cpp
new file mode 100644
index 00000000..3dcc8c3c
--- /dev/null
+++ b/examples/aflpp_driver/aflpp_driver.cpp
@@ -0,0 +1,281 @@
+//===- afl_driver.cpp - a glue between AFL and libFuzzer --------*- C++ -* ===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//===----------------------------------------------------------------------===//
+
+/* This file allows to fuzz libFuzzer-style target functions
+ (LLVMFuzzerTestOneInput) with AFL using AFL's persistent (in-process) mode.
+
+Usage:
+################################################################################
+cat << EOF > test_fuzzer.cc
+#include <stddef.h>
+#include <stdint.h>
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  if (size > 0 && data[0] == 'H')
+    if (size > 1 && data[1] == 'I')
+       if (size > 2 && data[2] == '!')
+       __builtin_trap();
+  return 0;
+}
+EOF
+# Build your target with -fsanitize-coverage=trace-pc-guard using fresh clang.
+clang -g -fsanitize-coverage=trace-pc-guard test_fuzzer.cc -c
+# Build afl-llvm-rt.o.c from the AFL distribution.
+clang -c -w $AFL_HOME/llvm_mode/afl-llvm-rt.o.c
+# Build this file, link it with afl-llvm-rt.o.o and the target code.
+clang++ afl_driver.cpp test_fuzzer.o afl-llvm-rt.o.o
+# Run AFL:
+rm -rf IN OUT; mkdir IN OUT; echo z > IN/z;
+$AFL_HOME/afl-fuzz -i IN -o OUT ./a.out
+################################################################################
+AFL_DRIVER_STDERR_DUPLICATE_FILENAME: Setting this *appends* stderr to the file
+specified. If the file does not exist, it is created. This is useful for getting
+stack traces (when using ASAN for example) or original error messages on hard
+to reproduce bugs. Note that any content written to stderr will be written to
+this file instead of stderr's usual location.
+
+AFL_DRIVER_CLOSE_FD_MASK: Similar to libFuzzer's -close_fd_mask behavior option.
+If 1, close stdout at startup. If 2 close stderr; if 3 close both.
+
+*/
+#include <assert.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <fstream>
+#include <iostream>
+#include <vector>
+
+// Platform detection. Copied from FuzzerInternal.h
+#ifdef __linux__
+#define LIBFUZZER_LINUX 1
+#define LIBFUZZER_APPLE 0
+#define LIBFUZZER_NETBSD 0
+#define LIBFUZZER_FREEBSD 0
+#define LIBFUZZER_OPENBSD 0
+#elif __APPLE__
+#define LIBFUZZER_LINUX 0
+#define LIBFUZZER_APPLE 1
+#define LIBFUZZER_NETBSD 0
+#define LIBFUZZER_FREEBSD 0
+#define LIBFUZZER_OPENBSD 0
+#elif __NetBSD__
+#define LIBFUZZER_LINUX 0
+#define LIBFUZZER_APPLE 0
+#define LIBFUZZER_NETBSD 1
+#define LIBFUZZER_FREEBSD 0
+#define LIBFUZZER_OPENBSD 0
+#elif __FreeBSD__
+#define LIBFUZZER_LINUX 0
+#define LIBFUZZER_APPLE 0
+#define LIBFUZZER_NETBSD 0
+#define LIBFUZZER_FREEBSD 1
+#define LIBFUZZER_OPENBSD 0
+#elif __OpenBSD__
+#define LIBFUZZER_LINUX 0
+#define LIBFUZZER_APPLE 0
+#define LIBFUZZER_NETBSD 0
+#define LIBFUZZER_FREEBSD 0
+#define LIBFUZZER_OPENBSD 1
+#else
+#error "Support for your platform has not been implemented"
+#endif
+
+int __afl_sharedmem_fuzzing = 1;
+extern unsigned int __afl_fuzz_len;
+extern unsigned char *__afl_fuzz_ptr;
+
+// libFuzzer interface is thin, so we don't include any libFuzzer headers.
+extern "C" {
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
+__attribute__((weak)) int LLVMFuzzerInitialize(int *argc, char ***argv);
+}
+
+// Notify AFL about persistent mode.
+static volatile char AFL_PERSISTENT[] = "##SIG_AFL_PERSISTENT##";
+extern "C" int __afl_persistent_loop(unsigned int);
+static volatile char suppress_warning2 = AFL_PERSISTENT[0];
+
+// Notify AFL about deferred forkserver.
+static volatile char AFL_DEFER_FORKSVR[] = "##SIG_AFL_DEFER_FORKSRV##";
+extern "C" void __afl_manual_init();
+static volatile char suppress_warning1 = AFL_DEFER_FORKSVR[0];
+
+// Input buffer.
+static const size_t kMaxAflInputSize = 1 << 20;
+static uint8_t AflInputBuf[kMaxAflInputSize];
+
+// Use this optionally defined function to output sanitizer messages even if
+// user asks to close stderr.
+__attribute__((weak)) extern "C" void __sanitizer_set_report_fd(void *);
+
+// Keep track of where stderr content is being written to, so that
+// dup_and_close_stderr can use the correct one.
+static FILE *output_file = stderr;
+
+// Experimental feature to use afl_driver without AFL's deferred mode.
+// Needs to run before __afl_auto_init.
+__attribute__((constructor(0))) static void __decide_deferred_forkserver(void) {
+  if (getenv("AFL_DRIVER_DONT_DEFER")) {
+    if (unsetenv("__AFL_DEFER_FORKSRV")) {
+      perror("Failed to unset __AFL_DEFER_FORKSRV");
+      abort();
+    }
+  }
+}
+
+// If the user asks us to duplicate stderr, then do it.
+static void maybe_duplicate_stderr() {
+  char *stderr_duplicate_filename =
+      getenv("AFL_DRIVER_STDERR_DUPLICATE_FILENAME");
+
+  if (!stderr_duplicate_filename)
+    return;
+
+  FILE *stderr_duplicate_stream =
+      freopen(stderr_duplicate_filename, "a+", stderr);
+
+  if (!stderr_duplicate_stream) {
+    fprintf(
+        stderr,
+        "Failed to duplicate stderr to AFL_DRIVER_STDERR_DUPLICATE_FILENAME");
+    abort();
+  }
+  output_file = stderr_duplicate_stream;
+}
+
+// Most of these I/O functions were inspired by/copied from libFuzzer's code.
+static void discard_output(int fd) {
+  FILE *temp = fopen("/dev/null", "w");
+  if (!temp)
+    abort();
+  dup2(fileno(temp), fd);
+  fclose(temp);
+}
+
+static void close_stdout() { discard_output(STDOUT_FILENO); }
+
+// Prevent the targeted code from writing to "stderr" but allow sanitizers and
+// this driver to do so.
+static void dup_and_close_stderr() {
+  int output_fileno = fileno(output_file);
+  int output_fd = dup(output_fileno);
+  if (output_fd <= 0)
+    abort();
+  FILE *new_output_file = fdopen(output_fd, "w");
+  if (!new_output_file)
+    abort();
+  if (!__sanitizer_set_report_fd)
+    return;
+  __sanitizer_set_report_fd(reinterpret_cast<void *>(output_fd));
+  discard_output(output_fileno);
+}
+
+static void Printf(const char *Fmt, ...) {
+  va_list ap;
+  va_start(ap, Fmt);
+  vfprintf(output_file, Fmt, ap);
+  va_end(ap);
+  fflush(output_file);
+}
+
+// Close stdout and/or stderr if user asks for it.
+static void maybe_close_fd_mask() {
+  char *fd_mask_str = getenv("AFL_DRIVER_CLOSE_FD_MASK");
+  if (!fd_mask_str)
+    return;
+  int fd_mask = atoi(fd_mask_str);
+  if (fd_mask & 2)
+    dup_and_close_stderr();
+  if (fd_mask & 1)
+    close_stdout();
+}
+
+// Define LLVMFuzzerMutate to avoid link failures for targets that use it
+// with libFuzzer's LLVMFuzzerCustomMutator.
+extern "C" size_t LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
+  assert(false && "LLVMFuzzerMutate should not be called from afl_driver");
+  return 0;
+}
+
+// Execute any files provided as parameters.
+static int ExecuteFilesOnyByOne(int argc, char **argv) {
+  for (int i = 1; i < argc; i++) {
+    std::ifstream in(argv[i], std::ios::binary);
+    in.seekg(0, in.end);
+    size_t length = in.tellg();
+    in.seekg (0, in.beg);
+    std::cout << "Reading " << length << " bytes from " << argv[i] << std::endl;
+    // Allocate exactly length bytes so that we reliably catch buffer overflows.
+    std::vector<char> bytes(length);
+    in.read(bytes.data(), bytes.size());
+    assert(in);
+    LLVMFuzzerTestOneInput(reinterpret_cast<const uint8_t *>(bytes.data()),
+                           bytes.size());
+    std::cout << "Execution successful" << std::endl;
+  }
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  Printf(
+      "======================= INFO =========================\n"
+      "This binary is built for AFL-fuzz.\n"
+      "To run the target function on individual input(s) execute this:\n"
+      "  %s < INPUT_FILE\n"
+      "or\n"
+      "  %s INPUT_FILE1 [INPUT_FILE2 ... ]\n"
+      "To fuzz with afl-fuzz execute this:\n"
+      "  afl-fuzz [afl-flags] %s [-N]\n"
+      "afl-fuzz will run N iterations before "
+      "re-spawning the process (default: 1000)\n"
+      "======================================================\n",
+          argv[0], argv[0], argv[0]);
+
+  maybe_duplicate_stderr();
+  maybe_close_fd_mask();
+  if (LLVMFuzzerInitialize)
+    LLVMFuzzerInitialize(&argc, &argv);
+  // Do any other expensive one-time initialization here.
+
+  int N = 1000;
+  if (argc == 2 && argv[1][0] == '-')
+      N = atoi(argv[1] + 1);
+  else if(argc == 2 && (N = atoi(argv[1])) > 0)
+      Printf("WARNING: using the deprecated call style `%s %d`\n", argv[0], N);
+  else if (argc > 1) {
+    if (!getenv("AFL_DRIVER_DONT_DEFER")) {
+      __afl_sharedmem_fuzzing = 0;
+      __afl_manual_init();
+    }
+    return ExecuteFilesOnyByOne(argc, argv);
+    exit(0);
+  }
+
+  assert(N > 0);
+
+  if (!getenv("AFL_DRIVER_DONT_DEFER"))
+    __afl_manual_init();
+
+  // Call LLVMFuzzerTestOneInput here so that coverage caused by initialization
+  // on the first execution of LLVMFuzzerTestOneInput is ignored.
+  uint8_t dummy_input[1] = {0};
+  LLVMFuzzerTestOneInput(dummy_input, 1);
+
+  int num_runs = 0;
+  while (__afl_persistent_loop(N)) {
+    if (__afl_fuzz_len > 0) {
+      num_runs++;
+      LLVMFuzzerTestOneInput(__afl_fuzz_ptr, __afl_fuzz_len);
+    }
+  }
+  Printf("%s: successfully executed %d input(s)\n", argv[0], num_runs);
+}