| // Copyright (c) 2011 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. |
| |
| // Fuzz testing for EncodedProgram serialized format and assembly. |
| // |
| // We would like some assurance that if an EncodedProgram is malformed we will |
| // not crash. The EncodedProgram could be malformed either due to malicious |
| // attack to due to an error in patch generation. |
| // |
| // We try a lot of arbitrary modifications to the serialized form and make sure |
| // that the outcome is not a crash. |
| #include "courgette/encoded_program.h" |
| |
| #include <stddef.h> |
| |
| #include "base/memory/scoped_ptr.h" |
| #include "base/test/test_suite.h" |
| #include "courgette/assembly_program.h" |
| #include "courgette/base_test_unittest.h" |
| #include "courgette/courgette.h" |
| #include "courgette/program_detector.h" |
| #include "courgette/streams.h" |
| |
| class DecodeFuzzTest : public BaseTest { |
| public: |
| void FuzzExe(const char *) const; |
| |
| private: |
| void FuzzByte(const std::string& buffer, const std::string& output, |
| size_t index) const; |
| void FuzzBits(const std::string& buffer, const std::string& output, |
| size_t index, int bits_to_flip) const; |
| |
| // Returns true if could assemble, false if rejected. |
| bool TryAssemble(const std::string& buffer, std::string* output) const; |
| }; |
| |
| // Loads an executable and does fuzz testing in the serialized format. |
| void DecodeFuzzTest::FuzzExe(const char* file_name) const { |
| std::string file1 = FileContents(file_name); |
| |
| const void* original_buffer = file1.c_str(); |
| size_t original_length = file1.length(); |
| |
| scoped_ptr<courgette::AssemblyProgram> program; |
| const courgette::Status parse_status = |
| courgette::ParseDetectedExecutable(original_buffer, original_length, |
| &program); |
| EXPECT_EQ(courgette::C_OK, parse_status); |
| |
| scoped_ptr<courgette::EncodedProgram> encoded; |
| const courgette::Status encode_status = Encode(*program, &encoded); |
| EXPECT_EQ(courgette::C_OK, encode_status); |
| |
| program.reset(); |
| |
| courgette::SinkStreamSet sinks; |
| const courgette::Status write_status = |
| WriteEncodedProgram(encoded.get(), &sinks); |
| EXPECT_EQ(courgette::C_OK, write_status); |
| |
| encoded.reset(); |
| |
| courgette::SinkStream sink; |
| bool can_collect = sinks.CopyTo(&sink); |
| EXPECT_TRUE(can_collect); |
| |
| size_t length = sink.Length(); |
| |
| std::string base_buffer(reinterpret_cast<const char*>(sink.Buffer()), length); |
| std::string base_output; |
| bool ok = TryAssemble(base_buffer, &base_output); |
| EXPECT_TRUE(ok); |
| |
| // Now we have a good serialized EncodedProgram in |base_buffer|. Time to |
| // fuzz. |
| |
| // More intense fuzzing on the first part because it contains more control |
| // information like substeam lengths. |
| size_t position = 0; |
| for ( ; position < 100 && position < length; position += 1) { |
| FuzzByte(base_buffer, base_output, position); |
| } |
| // We would love to fuzz every position, but it takes too long. |
| for ( ; position < length; position += 900) { |
| FuzzByte(base_buffer, base_output, position); |
| } |
| } |
| |
| // FuzzByte tries to break the EncodedProgram deserializer and assembler. It |
| // takes a good serialization of and EncodedProgram, flips some bits, and checks |
| // that the behaviour is reasonable. It has testing checks for unreasonable |
| // behaviours. |
| void DecodeFuzzTest::FuzzByte(const std::string& base_buffer, |
| const std::string& base_output, |
| size_t index) const { |
| printf("Fuzzing position %d\n", static_cast<int>(index)); |
| |
| // The following 10 values are a compromize between run time and coverage of |
| // the 255 'wrong' values at this byte position. |
| |
| // 0xFF flips all the bits. |
| FuzzBits(base_buffer, base_output, index, 0xFF); |
| // 0x7F flips the most bits without changing Varint32 framing. |
| FuzzBits(base_buffer, base_output, index, 0x7F); |
| // These all flip one bit. |
| FuzzBits(base_buffer, base_output, index, 0x80); |
| FuzzBits(base_buffer, base_output, index, 0x40); |
| FuzzBits(base_buffer, base_output, index, 0x20); |
| FuzzBits(base_buffer, base_output, index, 0x10); |
| FuzzBits(base_buffer, base_output, index, 0x08); |
| FuzzBits(base_buffer, base_output, index, 0x04); |
| FuzzBits(base_buffer, base_output, index, 0x02); |
| FuzzBits(base_buffer, base_output, index, 0x01); |
| } |
| |
| // FuzzBits tries to break the EncodedProgram deserializer and assembler. It |
| // takes a good serialization of and EncodedProgram, flips some bits, and checks |
| // that the behaviour is reasonable. |
| // |
| // There are EXPECT calls to check for unreasonable behaviour. These are |
| // somewhat arbitrary in that the parameters cannot easily be derived from first |
| // principles. They may need updating as the serialized format evolves. |
| void DecodeFuzzTest::FuzzBits(const std::string& base_buffer, |
| const std::string& base_output, |
| size_t index, int bits_to_flip) const { |
| std::string modified_buffer = base_buffer; |
| std::string modified_output; |
| modified_buffer[index] ^= bits_to_flip; |
| |
| bool ok = TryAssemble(modified_buffer, &modified_output); |
| |
| if (ok) { |
| // We normally expect TryAssemble to fail. But sometimes it succeeds. |
| // What could have happened? We changed one byte in the serialized form: |
| // |
| // * If we changed one of the copied bytes, we would see a single byte |
| // change in the output. |
| // * If we changed an address table element, all the references to that |
| // address would be different. |
| // * If we changed a copy count, we would run out of data in some stream, |
| // or leave data remaining, so should not be here. |
| // * If we changed an origin address, it could affect all relocations based |
| // off that address. If no relocations were based off the address then |
| // there will be no changes. |
| // * If we changed an origin address, it could cause some abs32 relocs to |
| // shift from one page to the next, changing the number and layout of |
| // blocks in the base relocation table. |
| |
| // Generated length could vary slightly due to base relocation table layout. |
| // In the worst case the number of base relocation blocks doubles, approx |
| // 12/4096 or 0.3% size of file. |
| size_t base_length = base_output.length(); |
| size_t modified_length = modified_output.length(); |
| ptrdiff_t diff = base_length - modified_length; |
| if (diff < -200 || diff > 200) { |
| EXPECT_EQ(base_length, modified_length); |
| } |
| |
| size_t changed_byte_count = 0; |
| for (size_t i = 0; i < base_length && i < modified_length; ++i) { |
| changed_byte_count += (base_output[i] != modified_output[i]); |
| } |
| |
| if (index > 60) { // Beyond the origin addresses ... |
| EXPECT_NE(0U, changed_byte_count); // ... we expect some difference. |
| } |
| // Currently all changes are smaller than this number: |
| EXPECT_GE(45000U, changed_byte_count); |
| } |
| } |
| |
| bool DecodeFuzzTest::TryAssemble(const std::string& buffer, |
| std::string* output) const { |
| scoped_ptr<courgette::EncodedProgram> encoded; |
| bool result = false; |
| |
| courgette::SourceStreamSet sources; |
| bool can_get_source_streams = sources.Init(buffer.c_str(), buffer.length()); |
| if (can_get_source_streams) { |
| const courgette::Status read_status = |
| ReadEncodedProgram(&sources, &encoded); |
| if (read_status == courgette::C_OK) { |
| courgette::SinkStream assembled; |
| const courgette::Status assemble_status = |
| Assemble(encoded.get(), &assembled); |
| |
| if (assemble_status == courgette::C_OK) { |
| const void* assembled_buffer = assembled.Buffer(); |
| size_t assembled_length = assembled.Length(); |
| |
| output->clear(); |
| output->assign(reinterpret_cast<const char*>(assembled_buffer), |
| assembled_length); |
| result = true; |
| } |
| } |
| } |
| |
| return result; |
| } |
| |
| TEST_F(DecodeFuzzTest, All) { |
| FuzzExe("setup1.exe"); |
| FuzzExe("elf-32-1.exe"); |
| } |
| |
| int main(int argc, char** argv) { |
| return base::TestSuite(argc, argv).Run(); |
| } |