[Zucchini] Add ELF fuzzer

This CL introduces a fuzzer for the ELF disassemblers in Zucchini. I
have already uploaded some corpus files to the clusterfuzz-corpus
Google Storage bucket.

Achieves ~700 exec/s locally. This is on-par with the DEX and Win32
disassemblers as it requires a largish representative file to serve
as a test. (Recommendation is ~1000 exec/s).

Brings up coverage of ELF related code from 0-30% to 80-100%

I expect this will find quite a few crashes early on but should
stabilize within a couple of weeks; est. 1-2 bugfixes per day
based on how DEX and Win32 went. Mostly checked_casts and bounds
issues.

Bug: 1013641
Change-Id: I205135547cad2a95e59f99d7f040c13d72c45b59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1856624
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705245}

components/zucchini/fuzzers/BUILD.gn

@@ -5,10 +5,21 @@
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//third_party/protobuf/proto_library.gni")
 
+static_library("zucchini_fuzz_utils") {
+  sources = [
+    "fuzz_utils.cc",
+    "fuzz_utils.h",
+  ]
+  deps = [
+    "//base",
+    "//components/zucchini:zucchini_lib",
+  ]
+}
+
 # To download the corpus for local fuzzing use:
 # gsutil -m rsync \
 #   gs://clusterfuzz-corpus/libfuzzer/zucchini_disassembler_dex_fuzzer \
-#   components/zucchini/fuzzing/testdata/disassembler_dex_fuzzer
+#   components/zucchini/fuzzing/testdata/disassembler_dex_fuzzer/
 fuzzer_test("zucchini_disassembler_dex_fuzzer") {
   sources = [
     "disassembler_dex_fuzzer.cc",
@@ -22,12 +33,28 @@ fuzzer_test("zucchini_disassembler_dex_fuzzer") {
 # To download the corpus for local fuzzing use:
 # gsutil -m rsync \
 #   gs://clusterfuzz-corpus/libfuzzer/zucchini_disassembler_win32_fuzzer \
-#   components/zucchini/fuzzing/testdata/disassembler_win32_fuzzer
+#   components/zucchini/fuzzing/testdata/disassembler_win32_fuzzer/
 fuzzer_test("zucchini_disassembler_win32_fuzzer") {
   sources = [
     "disassembler_win32_fuzzer.cc",
   ]
   deps = [
+    ":zucchini_fuzz_utils",
+    "//base",
+    "//components/zucchini:zucchini_lib",
+  ]
+}
+
+# To download the corpus for local fuzzing use:
+# gsutil -m rsync \
+#   gs://clusterfuzz-corpus/libfuzzer/zucchini_disassembler_elf_fuzzer \
+#   components/zucchini/fuzzing/testdata/disassembler_elf_fuzzer/
+fuzzer_test("zucchini_disassembler_elf_fuzzer") {
+  sources = [
+    "disassembler_elf_fuzzer.cc",
+  ]
+  deps = [
+    ":zucchini_fuzz_utils",
     "//base",
     "//components/zucchini:zucchini_lib",
   ]

components/zucchini/fuzzers/disassembler_elf_fuzzer.cc

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "components/zucchini/buffer_view.h"
+#include "components/zucchini/disassembler.h"
+#include "components/zucchini/disassembler_elf.h"
+#include "components/zucchini/fuzzers/fuzz_utils.h"
+
+namespace {
+
+struct Environment {
+  Environment() { logging::SetMinLogLevel(logging::LOG_FATAL); }
+};
+
+}  // namespace
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  static Environment env;
+  if (!size)
+    return 0;
+  // Prepare data.
+  std::vector<uint8_t> mutable_data(data, data + size);
+  zucchini::ConstBufferView image(mutable_data.data(), mutable_data.size());
+
+  // Create disassembler. Early exit on failure.
+  auto disassembler_elf_x64 =
+      zucchini::Disassembler::Make<zucchini::DisassemblerElfX64>(image);
+  if (disassembler_elf_x64) {
+    zucchini::ReadAndWriteReferences(std::move(disassembler_elf_x64),
+                                     &mutable_data);
+    return 0;
+  }
+
+  auto disassembler_elf_x86 =
+      zucchini::Disassembler::Make<zucchini::DisassemblerElfX86>(image);
+  if (disassembler_elf_x86)
+    zucchini::ReadAndWriteReferences(std::move(disassembler_elf_x86),
+                                     &mutable_data);
+  return 0;
+}

components/zucchini/fuzzers/disassembler_win32_fuzzer.cc

@@ -13,6 +13,7 @@
 #include "components/zucchini/buffer_view.h"
 #include "components/zucchini/disassembler.h"
 #include "components/zucchini/disassembler_win32.h"
+#include "components/zucchini/fuzzers/fuzz_utils.h"
 
 namespace {
 
@@ -22,33 +23,6 @@ struct Environment {
   }
 };
 
-// Helper function that uses |disassembler| to read all references from
-// |mutable_image| and write them back.
-void ReadAndWriteReferences(
-    std::unique_ptr<zucchini::Disassembler> disassembler,
-    std::vector<uint8_t>* mutable_data) {
-  zucchini::MutableBufferView mutable_image(mutable_data->data(),
-                                            disassembler->size());
-  std::vector<zucchini::Reference> references;
-  auto groups = disassembler->MakeReferenceGroups();
-  std::map<zucchini::PoolTag, std::vector<zucchini::Reference>>
-      references_of_pool;
-  for (const auto& group : groups) {
-    auto reader = group.GetReader(disassembler.get());
-    std::vector<zucchini::Reference>* refs =
-        &references_of_pool[group.pool_tag()];
-    for (auto ref = reader->GetNext(); ref.has_value();
-         ref = reader->GetNext()) {
-      refs->push_back(ref.value());
-    }
-  }
-  for (const auto& group : groups) {
-    auto writer = group.GetWriter(mutable_image, disassembler.get());
-    for (const auto& ref : references_of_pool[group.pool_tag()])
-      writer->PutNext(ref);
-  }
-}
-
 }  // namespace
 
 // Entry point for LibFuzzer.
@@ -64,13 +38,15 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   auto disassembler_win32x86 =
       zucchini::Disassembler::Make<zucchini::DisassemblerWin32X86>(image);
   if (disassembler_win32x86) {
-    ReadAndWriteReferences(std::move(disassembler_win32x86), &mutable_data);
+    zucchini::ReadAndWriteReferences(std::move(disassembler_win32x86),
+                                     &mutable_data);
     return 0;
   }
 
   auto disassembler_win32x64 =
       zucchini::Disassembler::Make<zucchini::DisassemblerWin32X64>(image);
   if (disassembler_win32x64)
-    ReadAndWriteReferences(std::move(disassembler_win32x64), &mutable_data);
+    zucchini::ReadAndWriteReferences(std::move(disassembler_win32x64),
+                                     &mutable_data);
   return 0;
 }

components/zucchini/fuzzers/fuzz_utils.cc

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/zucchini/fuzzers/fuzz_utils.h"
+
+#include <map>
+#include <memory>
+#include <vector>
+
+#include "components/zucchini/disassembler.h"
+
+namespace zucchini {
+
+void ReadAndWriteReferences(
+    std::unique_ptr<zucchini::Disassembler> disassembler,
+    std::vector<uint8_t>* mutable_data) {
+  zucchini::MutableBufferView mutable_image(mutable_data->data(),
+                                            disassembler->size());
+  std::vector<zucchini::Reference> references;
+  auto groups = disassembler->MakeReferenceGroups();
+  std::map<zucchini::PoolTag, std::vector<zucchini::Reference>>
+      references_of_pool;
+  for (const auto& group : groups) {
+    auto reader = group.GetReader(disassembler.get());
+    std::vector<zucchini::Reference>* refs =
+        &references_of_pool[group.pool_tag()];
+    for (auto ref = reader->GetNext(); ref.has_value();
+         ref = reader->GetNext()) {
+      refs->push_back(ref.value());
+    }
+  }
+  for (const auto& group : groups) {
+    auto writer = group.GetWriter(mutable_image, disassembler.get());
+    for (const auto& ref : references_of_pool[group.pool_tag()])
+      writer->PutNext(ref);
+  }
+}
+
+}  // namespace zucchini

components/zucchini/fuzzers/fuzz_utils.h

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_ZUCCHINI_FUZZERS_FUZZ_UTILS_H_
+#define COMPONENTS_ZUCCHINI_FUZZERS_FUZZ_UTILS_H_
+
+#include <stdint.h>
+
+#include <memory>
+#include <vector>
+
+#include "components/zucchini/disassembler.h"
+
+namespace zucchini {
+
+// Helper function that uses |disassembler| to read all references from
+// |mutable_data| and write them back.
+void ReadAndWriteReferences(
+    std::unique_ptr<zucchini::Disassembler> disassembler,
+    std::vector<uint8_t>* mutable_data);
+
+}  // namespace zucchini
+
+#endif  // COMPONENTS_ZUCCHINI_FUZZERS_FUZZ_UTILS_H_