// Copyright 2016 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 "courgette/disassembler_win32.h" #include #include "base/bind.h" #include "base/logging.h" #include "courgette/assembly_program.h" #include "courgette/courgette.h" #if COURGETTE_HISTOGRAM_TARGETS #include #endif namespace courgette { DisassemblerWin32::DisassemblerWin32(const uint8_t* start, size_t length) : Disassembler(start, length) {} RVA DisassemblerWin32::FileOffsetToRVA(FileOffset file_offset) const { for (int i = 0; i < number_of_sections_; ++i) { const Section* section = §ions_[i]; if (file_offset >= section->file_offset_of_raw_data) { FileOffset offset_in_section = file_offset - section->file_offset_of_raw_data; if (offset_in_section < section->size_of_raw_data) return static_cast(section->virtual_address + offset_in_section); } } NOTREACHED(); return kNoRVA; } FileOffset DisassemblerWin32::RVAToFileOffset(RVA rva) const { const Section* section = RVAToSection(rva); if (section != nullptr) { FileOffset offset_in_section = rva - section->virtual_address; // Need this extra check, since an |rva| may be valid for a section, but is // non-existent in an image (e.g. uninit data). if (offset_in_section >= section->size_of_raw_data) return kNoFileOffset; return static_cast(section->file_offset_of_raw_data + offset_in_section); } // Small RVA values point into the file header in the loaded image. // RVA 0 is the module load address which Windows uses as the module handle. // RVA 2 sometimes occurs, I'm not sure what it is, but it would map into the // DOS header. if (rva == 0 || rva == 2) return static_cast(rva); NOTREACHED(); return kNoFileOffset; } // ParseHeader attempts to match up the buffer with the Windows data // structures that exist within a Windows 'Portable Executable' format file. // Returns 'true' if the buffer matches, and 'false' if the data looks // suspicious. Rather than try to 'map' the buffer to the numerous windows // structures, we extract the information we need into the courgette::PEInfo // structure. // bool DisassemblerWin32::ParseHeader() { if (!IsRangeInBounds(kOffsetOfFileAddressOfNewExeHeader, 4)) return Bad("Too small"); // Have 'MZ' magic for a DOS header? if (start()[0] != 'M' || start()[1] != 'Z') return Bad("Not MZ"); // offset from DOS header to PE header is stored in DOS header. FileOffset pe_header_offset = static_cast( ReadU32(start(), kOffsetOfFileAddressOfNewExeHeader)); if (pe_header_offset % 8 != 0) return Bad("Misaligned PE header"); if (pe_header_offset < kOffsetOfFileAddressOfNewExeHeader + 4) return Bad("PE header pathological overlap"); if (!IsRangeInBounds(pe_header_offset, kMinPeHeaderSize)) return Bad("PE header past end of file"); const uint8_t* const pe_header = FileOffsetToPointer(pe_header_offset); // The 'PE' header is an IMAGE_NT_HEADERS structure as defined in WINNT.H. // See http://msdn.microsoft.com/en-us/library/ms680336(VS.85).aspx // // The first field of the IMAGE_NT_HEADERS is the signature. if (!(pe_header[0] == 'P' && pe_header[1] == 'E' && pe_header[2] == 0 && pe_header[3] == 0)) { return Bad("No PE signature"); } // The second field of the IMAGE_NT_HEADERS is the COFF header. // The COFF header is also called an IMAGE_FILE_HEADER // http://msdn.microsoft.com/en-us/library/ms680313(VS.85).aspx FileOffset coff_header_offset = pe_header_offset + 4; if (!IsRangeInBounds(coff_header_offset, kSizeOfCoffHeader)) return Bad("COFF header past end of file"); const uint8_t* const coff_header = start() + coff_header_offset; machine_type_ = ReadU16(coff_header, 0); number_of_sections_ = ReadU16(coff_header, 2); size_of_optional_header_ = ReadU16(coff_header, 16); // Check we can read the magic. if (size_of_optional_header_ < 2) return Bad("Optional header no magic"); // Check that we can read the rest of the the fixed fields. Data directories // directly follow the fixed fields of the IMAGE_OPTIONAL_HEADER. if (size_of_optional_header_ < RelativeOffsetOfDataDirectories()) return Bad("Optional header too short"); // The rest of the IMAGE_NT_HEADERS is the IMAGE_OPTIONAL_HEADER(32|64) FileOffset optional_header_offset = pe_header_offset + kMinPeHeaderSize; if (!IsRangeInBounds(optional_header_offset, size_of_optional_header_)) return Bad("Optional header past end of file"); optional_header_ = start() + optional_header_offset; uint16_t magic = ReadU16(optional_header_, 0); switch (kind()) { case EXE_WIN_32_X86: if (magic != kImageNtOptionalHdr32Magic) return Bad("64 bit executables are not supported by this disassembler"); break; case EXE_WIN_32_X64: if (magic != kImageNtOptionalHdr64Magic) return Bad("32 bit executables are not supported by this disassembler"); break; default: return Bad("Unrecognized magic"); } // The optional header is either an IMAGE_OPTIONAL_HEADER32 or // IMAGE_OPTIONAL_HEADER64 // http://msdn.microsoft.com/en-us/library/ms680339(VS.85).aspx // // Copy the fields we care about. size_of_code_ = ReadU32(optional_header_, 4); size_of_initialized_data_ = ReadU32(optional_header_, 8); size_of_uninitialized_data_ = ReadU32(optional_header_, 12); base_of_code_ = ReadU32(optional_header_, 20); switch (kind()) { case EXE_WIN_32_X86: base_of_data_ = ReadU32(optional_header_, 24); image_base_ = ReadU32(optional_header_, 28); size_of_image_ = ReadU32(optional_header_, 56); number_of_data_directories_ = ReadU32(optional_header_, 92); break; case EXE_WIN_32_X64: base_of_data_ = 0; image_base_ = ReadU64(optional_header_, 24); size_of_image_ = ReadU32(optional_header_, 56); number_of_data_directories_ = ReadU32(optional_header_, 108); break; default: NOTREACHED(); } if (size_of_image_ >= 0x80000000U) return Bad("Invalid SizeOfImage"); if (size_of_code_ >= length() || size_of_initialized_data_ >= length() || size_of_code_ + size_of_initialized_data_ >= length()) { // This validation fires on some perfectly fine executables. // return Bad("code or initialized data too big"); } // TODO(sra): we can probably get rid of most of the data directories. bool b = true; // 'b &= ...' could be short circuit 'b = b && ...' but it is not necessary // for correctness and it compiles smaller this way. b &= ReadDataDirectory(0, &export_table_); b &= ReadDataDirectory(1, &import_table_); b &= ReadDataDirectory(2, &resource_table_); b &= ReadDataDirectory(3, &exception_table_); b &= ReadDataDirectory(5, &base_relocation_table_); b &= ReadDataDirectory(11, &bound_import_table_); b &= ReadDataDirectory(12, &import_address_table_); b &= ReadDataDirectory(13, &delay_import_descriptor_); b &= ReadDataDirectory(14, &clr_runtime_header_); if (!b) return Bad("Malformed data directory"); // Sections follow the optional header. FileOffset sections_offset = optional_header_offset + size_of_optional_header_; if (!IsArrayInBounds(sections_offset, number_of_sections_, sizeof(Section))) return Bad("Sections past end of file"); sections_ = reinterpret_cast(start() + sections_offset); if (!CheckSectionRanges()) return Bad("Out of bound section"); size_t detected_length = 0; for (int i = 0; i < number_of_sections_; ++i) { const Section* section = §ions_[i]; // TODO(sra): consider using the 'characteristics' field of the section // header to see if the section contains instructions. if (memcmp(section->name, ".text", 6) == 0) has_text_section_ = true; uint32_t section_end = section->file_offset_of_raw_data + section->size_of_raw_data; if (section_end > detected_length) detected_length = section_end; } // Pretend our in-memory copy is only as long as our detected length. ReduceLength(detected_length); if (!has_text_section()) { return Bad("Resource-only executables are not yet supported"); } return Good(); } //////////////////////////////////////////////////////////////////////////////// bool DisassemblerWin32::ParseRelocs(std::vector* relocs) { relocs->clear(); size_t relocs_size = base_relocation_table_.size_; if (relocs_size == 0) return true; // The format of the base relocation table is a sequence of variable sized // IMAGE_BASE_RELOCATION blocks. Search for // "The format of the base relocation data is somewhat quirky" // at http://msdn.microsoft.com/en-us/library/ms809762.aspx const uint8_t* relocs_start = RVAToPointer(base_relocation_table_.address_); if (relocs_start == nullptr || relocs_start < start() || relocs_start >= end()) return Bad(".relocs outside image"); // Make sure entire base relocation table is within the buffer. if (relocs_size > static_cast(end() - relocs_start)) return Bad(".relocs outside image"); const uint8_t* relocs_end = relocs_start + relocs_size; const uint8_t* block = relocs_start; // Walk the variable sized blocks. while (block + 8 < relocs_end) { RVA page_rva = ReadU32(block, 0); uint32_t size = ReadU32(block, 4); if (size < 8 || // Size includes header ... size % 4 != 0) // ... and is word aligned. return Bad("Unreasonable relocs block"); const uint8_t* end_entries = block + size; if (end_entries <= block || end_entries <= start() || end_entries > end()) return Bad(".relocs block outside image"); // Walk through the two-byte entries. for (const uint8_t* p = block + 8; p < end_entries; p += 2) { uint16_t entry = ReadU16(p, 0); int type = entry >> 12; int offset = entry & 0xFFF; RVA rva = page_rva + offset; // Skip the relocs that live outside of the image. It might be the case // if a reloc is relative to a register, e.g.: // mov ecx,dword ptr [eax+044D5888h] RVA target_rva = PointerToTargetRVA(RVAToPointer(rva)); if (target_rva == kNoRVA) { continue; } if (SupportsRelTableType(type)) { relocs->push_back(rva); } else if (type == 0) { // IMAGE_REL_BASED_ABSOLUTE // Ignore, used as padding. } else { // Does not occur in Windows x86/x64 executables. return Bad("Unknown type of reloc"); } } block += size; } std::sort(relocs->begin(), relocs->end()); DCHECK(relocs->empty() || relocs->back() != kUnassignedRVA); return true; } const Section* DisassemblerWin32::RVAToSection(RVA rva) const { for (int i = 0; i < number_of_sections_; ++i) { const Section* section = §ions_[i]; if (rva >= section->virtual_address) { FileOffset offset_in_section = rva - section->virtual_address; if (offset_in_section < section->virtual_size) return section; } } return nullptr; } std::string DisassemblerWin32::SectionName(const Section* section) { if (section == nullptr) return ""; char name[9]; memcpy(name, section->name, 8); name[8] = '\0'; // Ensure termination. return name; } // static bool DisassemblerWin32::QuickDetect(const uint8_t* start, size_t length, uint16_t magic) { if (length < kOffsetOfFileAddressOfNewExeHeader + 4) return false; // Have 'MZ' magic for a DOS header? if (start[0] != 'M' || start[1] != 'Z') return false; FileOffset pe_header_offset = static_cast( ReadU32(start, kOffsetOfFileAddressOfNewExeHeader)); if (pe_header_offset % 8 != 0 || pe_header_offset < kOffsetOfFileAddressOfNewExeHeader + 4 || pe_header_offset >= length || length - pe_header_offset < kMinPeHeaderSize) { return false; } const uint8_t* pe_header = start + pe_header_offset; if (!(pe_header[0] == 'P' && pe_header[1] == 'E' && pe_header[2] == 0 && pe_header[3] == 0)) { return false; } FileOffset optional_header_offset = pe_header_offset + kMinPeHeaderSize; if (optional_header_offset >= length || length - optional_header_offset < 2) return false; const uint8_t* optional_header = start + optional_header_offset; return magic == ReadU16(optional_header, 0); } bool DisassemblerWin32::IsRvaRangeInBounds(size_t start, size_t length) { return start < size_of_image_ && length <= size_of_image_ - start; } bool DisassemblerWin32::CheckSectionRanges() { for (int i = 0; i < number_of_sections_; ++i) { const Section* section = §ions_[i]; if (!IsRangeInBounds(section->file_offset_of_raw_data, section->size_of_raw_data) || !IsRvaRangeInBounds(section->virtual_address, section->virtual_size)) { return false; } } return true; } bool DisassemblerWin32::ExtractAbs32Locations() { abs32_locations_.clear(); if (!ParseRelocs(&abs32_locations_)) return false; #if COURGETTE_HISTOGRAM_TARGETS for (size_t i = 0; i < abs32_locations_.size(); ++i) { RVA rva = abs32_locations_[i]; // The 4 bytes at the relocation are a reference to some address. ++abs32_target_rvas_[PointerToTargetRVA(RVAToPointer(rva))]; } #endif return true; } bool DisassemblerWin32::ExtractRel32Locations() { FileOffset file_offset = 0; while (file_offset < length()) { const Section* section = FindNextSection(file_offset); if (section == nullptr) break; if (file_offset < section->file_offset_of_raw_data) file_offset = section->file_offset_of_raw_data; ParseRel32RelocsFromSection(section); file_offset += section->size_of_raw_data; } std::sort(rel32_locations_.begin(), rel32_locations_.end()); DCHECK(rel32_locations_.empty() || rel32_locations_.back() != kUnassignedRVA); #if COURGETTE_HISTOGRAM_TARGETS VLOG(1) << "abs32_locations_ " << abs32_locations_.size() << "\nrel32_locations_ " << rel32_locations_.size() << "\nabs32_target_rvas_ " << abs32_target_rvas_.size() << "\nrel32_target_rvas_ " << rel32_target_rvas_.size(); int common = 0; std::map::iterator abs32_iter = abs32_target_rvas_.begin(); std::map::iterator rel32_iter = rel32_target_rvas_.begin(); while (abs32_iter != abs32_target_rvas_.end() && rel32_iter != rel32_target_rvas_.end()) { if (abs32_iter->first < rel32_iter->first) { ++abs32_iter; } else if (rel32_iter->first < abs32_iter->first) { ++rel32_iter; } else { ++common; ++abs32_iter; ++rel32_iter; } } VLOG(1) << "common " << common; #endif return true; } RvaVisitor* DisassemblerWin32::CreateAbs32TargetRvaVisitor() { return new RvaVisitor_Abs32(abs32_locations_, *this); } RvaVisitor* DisassemblerWin32::CreateRel32TargetRvaVisitor() { return new RvaVisitor_Rel32(rel32_locations_, *this); } void DisassemblerWin32::RemoveUnusedRel32Locations( AssemblyProgram* program) { auto cond = [this, program](RVA rva) -> bool { // + 4 since offset is relative to start of next instruction. RVA target_rva = rva + 4 + Read32LittleEndian(RVAToPointer(rva)); return program->FindRel32Label(target_rva) == nullptr; }; rel32_locations_.erase( std::remove_if(rel32_locations_.begin(), rel32_locations_.end(), cond), rel32_locations_.end()); } InstructionGenerator DisassemblerWin32::GetInstructionGenerator( AssemblyProgram* program) { return base::BindRepeating(&DisassemblerWin32::ParseFile, base::Unretained(this), program); } CheckBool DisassemblerWin32::ParseFile(AssemblyProgram* program, InstructionReceptor* receptor) const { // Walk all the bytes in the file, whether or not in a section. FileOffset file_offset = 0; while (file_offset < length()) { const Section* section = FindNextSection(file_offset); if (section == nullptr) { // No more sections. There should not be extra stuff following last // section. // ParseNonSectionFileRegion(file_offset, pe_info().length(), receptor); break; } if (file_offset < section->file_offset_of_raw_data) { FileOffset section_start_offset = section->file_offset_of_raw_data; if (!ParseNonSectionFileRegion(file_offset, section_start_offset, receptor)) { return false; } file_offset = section_start_offset; } FileOffset end = file_offset + section->size_of_raw_data; if (!ParseFileRegion(section, file_offset, end, program, receptor)) return false; file_offset = end; } #if COURGETTE_HISTOGRAM_TARGETS HistogramTargets("abs32 relocs", abs32_target_rvas_); HistogramTargets("rel32 relocs", rel32_target_rvas_); #endif return true; } CheckBool DisassemblerWin32::ParseNonSectionFileRegion( FileOffset start_file_offset, FileOffset end_file_offset, InstructionReceptor* receptor) const { if (incomplete_disassembly_) return true; if (end_file_offset > start_file_offset) { if (!receptor->EmitMultipleBytes(FileOffsetToPointer(start_file_offset), end_file_offset - start_file_offset)) { return false; } } return true; } CheckBool DisassemblerWin32::ParseFileRegion( const Section* section, FileOffset start_file_offset, FileOffset end_file_offset, AssemblyProgram* program, InstructionReceptor* receptor) const { RVA relocs_start_rva = base_relocation_table().address_; const uint8_t* start_pointer = FileOffsetToPointer(start_file_offset); const uint8_t* end_pointer = FileOffsetToPointer(end_file_offset); RVA start_rva = FileOffsetToRVA(start_file_offset); RVA end_rva = start_rva + section->virtual_size; const int kVAWidth = AbsVAWidth(); // Quick way to convert from Pointer to RVA within a single Section is to // subtract 'pointer_to_rva'. const uint8_t* const adjust_pointer_to_rva = start_pointer - start_rva; std::vector::const_iterator rel32_pos = rel32_locations_.begin(); std::vector::const_iterator abs32_pos = abs32_locations_.begin(); if (!receptor->EmitOrigin(start_rva)) return false; const uint8_t* p = start_pointer; while (p < end_pointer) { RVA current_rva = static_cast(p - adjust_pointer_to_rva); // The base relocation table is usually in the .relocs section, but it could // actually be anywhere. Make sure we skip it because we will regenerate it // during assembly. if (current_rva == relocs_start_rva) { if (!receptor->EmitPeRelocs()) return false; uint32_t relocs_size = base_relocation_table().size_; if (relocs_size) { p += relocs_size; continue; } } while (abs32_pos != abs32_locations_.end() && *abs32_pos < current_rva) ++abs32_pos; if (abs32_pos != abs32_locations_.end() && *abs32_pos == current_rva) { RVA target_rva = PointerToTargetRVA(p); DCHECK_NE(kNoRVA, target_rva); // TODO(sra): target could be Label+offset. It is not clear how to guess // which it might be. We assume offset==0. Label* label = program->FindAbs32Label(target_rva); DCHECK(label); if (!EmitAbs(label, receptor)) return false; p += kVAWidth; continue; } while (rel32_pos != rel32_locations_.end() && *rel32_pos < current_rva) ++rel32_pos; if (rel32_pos != rel32_locations_.end() && *rel32_pos == current_rva) { // + 4 since offset is relative to start of next instruction. RVA target_rva = current_rva + 4 + Read32LittleEndian(p); Label* label = program->FindRel32Label(target_rva); DCHECK(label); if (!receptor->EmitRel32(label)) return false; p += 4; continue; } if (incomplete_disassembly_) { if ((abs32_pos == abs32_locations_.end() || end_rva <= *abs32_pos) && (rel32_pos == rel32_locations_.end() || end_rva <= *rel32_pos) && (end_rva <= relocs_start_rva || current_rva >= relocs_start_rva)) { // No more relocs in this section, don't bother encoding bytes. break; } } if (!receptor->EmitSingleByte(*p)) return false; p += 1; } return true; } #if COURGETTE_HISTOGRAM_TARGETS // Histogram is printed to std::cout. It is purely for debugging the algorithm // and is only enabled manually in 'exploration' builds. I don't want to add // command-line configuration for this feature because this code has to be // small, which means compiled-out. void DisassemblerWin32::HistogramTargets(const char* kind, const std::map& map) const { int total = 0; std::map> h; for (std::map::const_iterator p = map.begin(); p != map.end(); ++p) { h[p->second].push_back(p->first); total += p->second; } std::cout << total << " " << kind << " to " << map.size() << " unique targets" << std::endl; std::cout << "indegree: #targets-with-indegree (example)" << std::endl; const int kFirstN = 15; bool someSkipped = false; int index = 0; for (std::map>::reverse_iterator p = h.rbegin(); p != h.rend(); ++p) { ++index; if (index <= kFirstN || p->first <= 3) { if (someSkipped) { std::cout << "..." << std::endl; } size_t count = p->second.size(); std::cout << std::dec << p->first << ": " << count; if (count <= 2) { for (size_t i = 0; i < count; ++i) std::cout << " " << DescribeRVA(p->second[i]); } std::cout << std::endl; someSkipped = false; } else { someSkipped = true; } } } #endif // COURGETTE_HISTOGRAM_TARGETS // DescribeRVA is for debugging only. I would put it under #ifdef DEBUG except // that during development I'm finding I need to call it when compiled in // Release mode. Hence: // TODO(sra): make this compile only for debug mode. std::string DisassemblerWin32::DescribeRVA(RVA rva) const { const Section* section = RVAToSection(rva); std::ostringstream s; s << std::hex << rva; if (section) { s << " ("; s << SectionName(section) << "+" << std::hex << (rva - section->virtual_address) << ")"; } return s.str(); } const Section* DisassemblerWin32::FindNextSection( FileOffset file_offset) const { const Section* best = nullptr; for (int i = 0; i < number_of_sections_; ++i) { const Section* section = §ions_[i]; if (section->size_of_raw_data > 0) { // i.e. has data in file. if (file_offset <= section->file_offset_of_raw_data) { if (best == nullptr || section->file_offset_of_raw_data < best->file_offset_of_raw_data) { best = section; } } } } return best; } bool DisassemblerWin32::ReadDataDirectory(int index, ImageDataDirectory* directory) { if (index < number_of_data_directories_) { FileOffset file_offset = index * 8 + RelativeOffsetOfDataDirectories(); if (file_offset >= size_of_optional_header_) return Bad("Number of data directories inconsistent"); const uint8_t* data_directory = optional_header_ + file_offset; if (data_directory < start() || data_directory + 8 >= end()) return Bad("Data directory outside image"); RVA rva = ReadU32(data_directory, 0); size_t size = ReadU32(data_directory, 4); if (size > size_of_image_) return Bad("Data directory size too big"); // TODO(sra): validate RVA. directory->address_ = rva; directory->size_ = static_cast(size); return true; } else { directory->address_ = 0; directory->size_ = 0; return true; } } } // namespace courgette