From 4f8d228278594b81d27b4ecb83c01670ef5ab33f Mon Sep 17 00:00:00 2001
From: Matt Borgerson <contact@mborgerson.com>
Date: Thu, 24 Aug 2023 18:45:20 -0700
Subject: [PATCH] Add basic COFF (.obj) file support

---
 cle/__init__.py          |   2 +
 cle/backends/__init__.py |   2 +
 cle/backends/coff.py     | 516 +++++++++++++++++++++++++++++++++++++++
 tests/test_coff.py       |  36 +++
 4 files changed, 556 insertions(+)
 create mode 100644 cle/backends/coff.py
 create mode 100644 tests/test_coff.py

diff --git a/cle/__init__.py b/cle/__init__.py
index ab1b072b..c63f6a3c 100644
--- a/cle/__init__.py
+++ b/cle/__init__.py
@@ -19,6 +19,7 @@
     BackedCGC,
     Backend,
     Blob,
+    Coff,
     ELFCore,
     ExceptionHandling,
     FunctionHint,
@@ -81,6 +82,7 @@
     "BackedCGC",
     "Backend",
     "Blob",
+    "Coff",
     "ELFCore",
     "ExceptionHandling",
     "FunctionHint",
diff --git a/cle/backends/__init__.py b/cle/backends/__init__.py
index fe9bfe3e..62d31b86 100644
--- a/cle/backends/__init__.py
+++ b/cle/backends/__init__.py
@@ -1,6 +1,7 @@
 from .backend import ALL_BACKENDS, Backend, ExceptionHandling, FunctionHint, FunctionHintSource, register_backend
 from .blob import Blob
 from .cgc import CGC, BackedCGC
+from .coff import Coff
 from .elf import ELF, ELFCore, MetaELF
 from .ihex import Hex
 from .java.apk import Apk
@@ -32,6 +33,7 @@
     "ELFCore",
     "MetaELF",
     "PE",
+    "Coff",
     "Blob",
     "CGC",
     "BackedCGC",
diff --git a/cle/backends/coff.py b/cle/backends/coff.py
new file mode 100644
index 00000000..889bcc60
--- /dev/null
+++ b/cle/backends/coff.py
@@ -0,0 +1,516 @@
+"""
+Basic MS COFF object loader based on https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
+"""
+import ctypes
+import logging
+import struct
+from enum import IntEnum, IntFlag
+from typing import Dict, Optional, Sequence, Type
+
+import archinfo
+
+from .backend import Backend, register_backend
+from .region import Section, Segment
+from .relocation import Relocation
+from .symbol import Symbol, SymbolType
+
+log = logging.getLogger(__name__)
+
+
+class IMAGE_FILE_MACHINE(IntEnum):
+    """
+    Machine Types
+    """
+
+    I386 = 0x14C
+    AMD64 = 0x8664
+
+
+class CoffFileHeader(ctypes.LittleEndianStructure):
+    """
+    COFF File Header
+    """
+
+    _pack_ = 1
+    _fields_ = [
+        ("Machine", ctypes.c_uint16),
+        ("NumberOfSections", ctypes.c_uint16),
+        ("TimeDateStamp", ctypes.c_uint32),
+        ("PointerToSymbolTable", ctypes.c_uint32),
+        ("NumberOfSymbols", ctypes.c_uint32),
+        ("SizeOfOptionalHeader", ctypes.c_uint16),
+        ("Characteristics", ctypes.c_uint16),
+    ]
+
+
+class IMAGE_SCN(IntFlag):
+    """
+    Section Flags (Characteristics field)
+    """
+
+    MEM_EXECUTE = 0x20000000
+    MEM_READ = 0x40000000
+    MEM_WRITE = 0x80000000
+    CNT_UNINITIALIZED_DATA = 0x00000080
+
+
+class CoffSectionTableEntry(ctypes.LittleEndianStructure):
+    """
+    COFF Section Header
+    """
+
+    _pack_ = 1
+    _fields_ = [
+        ("Name", ctypes.c_uint8 * 8),
+        ("VirtualSize", ctypes.c_uint32),
+        ("VirtualAddress", ctypes.c_uint32),
+        ("SizeOfRawData", ctypes.c_uint32),
+        ("PointerToRawData", ctypes.c_uint32),
+        ("PointerToRelocations", ctypes.c_uint32),
+        ("PointerToLinenumbers", ctypes.c_uint32),
+        ("NumberOfRelocations", ctypes.c_uint16),
+        ("NumberOfLinenumbers", ctypes.c_uint16),
+        ("Characteristics", ctypes.c_uint32),
+    ]
+
+
+class IMAGE_SYM_CLASS(IntEnum):
+    """
+    Symbol Storage Class
+    """
+
+    EXTERNAL = 2
+    STATIC = 3
+    LABEL = 6
+    FUNCTION = 101
+
+
+class CoffSymbolTableEntry(ctypes.LittleEndianStructure):
+    """
+    COFF Symbol Table Entry
+    """
+
+    _pack_ = 1
+    _fields_ = [
+        ("Name", ctypes.c_uint8 * 8),
+        ("Value", ctypes.c_uint32),
+        ("SectionNumber", ctypes.c_int16),
+        ("Type", ctypes.c_uint16),
+        ("StorageClass", ctypes.c_uint8),
+        ("NumberOfAuxSymbols", ctypes.c_uint8),
+    ]
+
+
+class IMAGE_REL_I386(IntEnum):
+    """
+    i386 Relocation Types
+    """
+
+    DIR32 = 0x0006
+    DIR32NB = 0x0007
+    REL32 = 0x0014
+    SECTION = 0x000A
+    SECREL = 0x000B
+
+
+class IMAGE_REL_AMD64(IntEnum):
+    """
+    AMD64 Relocation Types
+    """
+
+    ADDR64 = 0x0001
+    ADDR32NB = 0x0003
+    REL32 = 0x0004
+    SECTION = 0x000A
+    SECREL = 0x000B
+
+
+class CoffRelocationTableEntry(ctypes.LittleEndianStructure):
+    """
+    COFF Relocations
+    """
+
+    _pack_ = 1
+    _fields_ = [
+        ("VirtualAddress", ctypes.c_uint32),
+        ("SymbolTableIndex", ctypes.c_uint32),
+        ("Type", ctypes.c_uint16),
+    ]
+
+
+class CoffParser:
+    """
+    Parses COFF object files.
+    """
+
+    data: bytes
+    header: CoffFileHeader
+    sections: Sequence[CoffSectionTableEntry]
+    relocations: Sequence[Sequence[CoffRelocationTableEntry]]
+    symbols: Sequence[CoffSymbolTableEntry]
+
+    # Note: Symbols are uniquely identified by their index. It is possible for multiple symbols to have the same name so
+    # in idx_to_symbol_name and symbol_name_to_idx, numeric suffixes are appended when necessary. To get the true name
+    # of a symbol at index `symbol_idx`, call get_symbol_name(symbol_idx, true_name=True).
+    idx_to_symbol_name: Dict[int, str]
+    symbol_name_to_idx: Dict[str, int]
+
+    def __init__(self, data: bytes):
+        if data.startswith(b"\x00\x00\xff\xff"):
+            raise ValueError(
+                "This object file appears to have been compiled with whole program optimization (/GL flag)"
+                " and cannot be parsed by this library"
+            )
+        self.data: bytes = data
+        self._parse()
+
+    def _parse(self) -> None:
+        self.header = CoffFileHeader.from_buffer_copy(self.data)
+        if self.header.Machine not in {
+            IMAGE_FILE_MACHINE.I386,
+            IMAGE_FILE_MACHINE.AMD64,
+        }:
+            raise NotImplementedError("Unsupported machine type")
+
+        strings_offset = (
+            self.header.PointerToSymbolTable + ctypes.sizeof(CoffSymbolTableEntry) * self.header.NumberOfSymbols
+        )
+        strings_size = struct.unpack("<I", self.data[strings_offset : strings_offset + 4])[0]
+        self.strings: bytes = self.data[strings_offset : strings_offset + strings_size]
+
+        self.symbols = []
+        self.symbol_name_to_idx = {}
+        self.idx_to_symbol_name = {}
+
+        offset = self.header.PointerToSymbolTable
+        aux = 0
+        for i in range(self.header.NumberOfSymbols):
+            symbol = CoffSymbolTableEntry.from_buffer_copy(self.data, offset)
+            offset += ctypes.sizeof(CoffSymbolTableEntry)
+            self.symbols.append(symbol)
+            if aux:
+                aux -= 1
+                continue
+            idx = len(self.symbols) - 1
+            name = self.get_symbol_name(idx)
+            aux = symbol.NumberOfAuxSymbols
+
+            # Ensure unique symbol names
+            i = 1
+            base_name = name
+            while name in self.symbol_name_to_idx:
+                name = base_name + f"__{i}"
+                i += 1
+            self.symbol_name_to_idx[name] = idx
+            self.idx_to_symbol_name[idx] = name
+
+        self.sections = []
+        self.relocations = []
+
+        for i in range(self.header.NumberOfSections):
+            offset = ctypes.sizeof(self.header) + ctypes.sizeof(CoffSectionTableEntry) * i
+            section = CoffSectionTableEntry.from_buffer_copy(self.data, offset)
+            self.sections.append(section)
+
+            # Relocations
+            relocs = []
+            offset = section.PointerToRelocations
+            for i in range(section.NumberOfRelocations):
+                reloc = CoffRelocationTableEntry.from_buffer_copy(self.data, offset)
+                relocs.append(reloc)
+                offset += ctypes.sizeof(reloc)
+            self.relocations.append(relocs)
+
+    @staticmethod
+    def _decode_cstring(data: bytes, offset: int, encoding: Optional[str] = None) -> str:
+        name = bytearray()
+        while True:
+            x = data[offset]
+            if x == 0:
+                break
+            name.append(x)
+            offset += 1
+        return str(name, encoding=(encoding or "ascii"))
+
+    def get_symbol_name(self, symbol_idx: int, true_name: bool = False) -> str:
+        if symbol_idx in self.idx_to_symbol_name and not true_name:
+            return self.idx_to_symbol_name[symbol_idx]
+
+        name_encoded = bytes(self.symbols[symbol_idx].Name)
+        if name_encoded[0:4] == b"\x00\x00\x00\x00":
+            offset = struct.unpack("<II", name_encoded)[1]
+            return self._decode_cstring(self.strings, offset)
+        return name_encoded.rstrip(b"\x00").decode("ascii")
+
+    def get_section_name(self, section_idx: int) -> str:
+        name = bytes(self.sections[section_idx].Name).rstrip(b"\x00").decode("ascii")
+        if name.startswith("/"):
+            return self.get_symbol_name(int(name[1:]))
+        return name
+
+
+class CoffSection(Section):
+    """
+    Section of the COFF object.
+    """
+
+    def __init__(
+        self,
+        name: str,
+        file_offset: int,
+        file_size: int,
+        virtual_addr: int,
+        virtual_size: int,
+        coff_sec: CoffSectionTableEntry,
+    ):
+        super().__init__(name, file_offset, virtual_addr, virtual_size)
+        self.filesize = file_size
+        self._coff_sec = coff_sec
+
+    @property
+    def is_readable(self):
+        return (self._coff_sec.Characteristics & IMAGE_SCN.MEM_READ) != 0
+
+    @property
+    def is_writable(self):
+        return (self._coff_sec.Characteristics & IMAGE_SCN.MEM_WRITE) != 0
+
+    @property
+    def is_executable(self):
+        return (self._coff_sec.Characteristics & IMAGE_SCN.MEM_EXECUTE) != 0
+
+    @property
+    def only_contains_uninitialized_data(self):
+        return (self._coff_sec.Characteristics & IMAGE_SCN.CNT_UNINITIALIZED_DATA) != 0
+
+
+class CoffRelocation(Relocation):
+    """
+    Relocation for a COFF object.
+    """
+
+    def relocate(self):
+        value = self.value
+        if value is None:
+            log.debug("Unresolved relocation with no symbol.")
+            return
+        self.owner.memory.store(self.relative_addr, value)
+
+
+class CoffRelocationREL32(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_*_REL32
+    """
+
+    @property
+    def value(self):
+        org_bytes = self.owner.memory.load(self.relative_addr, 4)
+        org_value = struct.unpack("<I", org_bytes)[0]
+        return struct.pack("<i", org_value + self.resolvedby.rebased_addr - (self.rebased_addr + 4))
+
+
+class CoffRelocationDIR32(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_*_DIR32
+    """
+
+    @property
+    def value(self):
+        org_bytes = self.owner.memory.load(self.relative_addr, 4)
+        org_value = struct.unpack("<I", org_bytes)[0]
+        return struct.pack("<i", org_value + self.resolvedby.rebased_addr)
+
+
+class CoffRelocationDIR32NB(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_*_DIR32
+    """
+
+    @property
+    def value(self):
+        org_bytes = self.owner.memory.load(self.relative_addr, 4)
+        org_value = struct.unpack("<I", org_bytes)[0]
+        return struct.pack("<i", org_value + self.resolvedby.relative_addr)
+
+
+class CoffRelocationADDR32NB(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_AMD64_ADDR32NB
+    """
+
+    @property
+    def value(self):
+        return struct.pack("<I", self.resolvedby.relative_addr)
+
+
+class CoffRelocationADDR64(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_AMD64_ADDR64
+    """
+
+    @property
+    def value(self):
+        return struct.pack("<Q", self.resolvedby.rebased_addr)
+
+
+class CoffRelocationSECTION(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_*_SECTION
+    """
+
+    @property
+    def value(self):
+        assert isinstance(self.owner, Coff)
+        section_idx = 0  # FIXME
+        return struct.pack("<H", section_idx)
+
+
+class CoffRelocationSECREL(CoffRelocation):
+    """
+    Relocation for IMAGE_REL_*_SECREL
+    """
+
+    @property
+    def value(self):
+        assert isinstance(self.owner, Coff)
+        offset_to_symbol = 0  # FIXME
+        return struct.pack("<I", offset_to_symbol)
+
+
+RELOC_CLASSES: Dict[IntEnum, Dict[IntEnum, Type[Relocation]]] = {
+    IMAGE_FILE_MACHINE.I386: {
+        IMAGE_REL_I386.REL32: CoffRelocationREL32,
+        IMAGE_REL_I386.DIR32: CoffRelocationDIR32,
+        IMAGE_REL_I386.DIR32NB: CoffRelocationDIR32NB,
+        IMAGE_REL_I386.SECTION: CoffRelocationSECTION,
+        IMAGE_REL_I386.SECREL: CoffRelocationSECREL,
+    },
+    IMAGE_FILE_MACHINE.AMD64: {
+        IMAGE_REL_AMD64.ADDR64: CoffRelocationADDR64,
+        IMAGE_REL_AMD64.ADDR32NB: CoffRelocationADDR32NB,
+        IMAGE_REL_AMD64.REL32: CoffRelocationREL32,
+        IMAGE_REL_AMD64.SECTION: CoffRelocationSECTION,
+        IMAGE_REL_AMD64.SECREL: CoffRelocationSECREL,
+    },
+}
+
+COFF_MACHINE_TO_ARCH_NAME = {
+    IMAGE_FILE_MACHINE.I386: "x86",
+    IMAGE_FILE_MACHINE.AMD64: "AMD64",
+}
+
+
+class Coff(Backend):
+    """
+    COFF object loader.
+    """
+
+    is_default = True
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        if self.binary is None:
+            self._data = self._binary_stream.read()
+        else:
+            with open(self.binary, "rb") as f:
+                self._data = f.read()
+
+        self._coff = CoffParser(self._data)
+
+        arch = archinfo.arch_from_id(COFF_MACHINE_TO_ARCH_NAME[self._coff.header.Machine])
+        self.set_arch(arch)
+
+        # FIXME: Currently we just map the whole object file for convenience. Create a better memory map from the
+        # section, discarding object file structure data.
+        self._image_vmem = self._data
+
+        # Add each section
+        for section_idx, section in enumerate(self._coff.sections):
+            section_name = self._coff.get_section_name(section_idx)
+            vaddr = section.PointerToRawData
+            vsize = section.SizeOfRawData
+            self.segments.append(Segment(section.PointerToRawData, vaddr, section.SizeOfRawData, vsize))
+            self.sections.append(
+                CoffSection(
+                    section_name,
+                    section.PointerToRawData,
+                    section.SizeOfRawData,
+                    vaddr,
+                    vsize,
+                    section,
+                )
+            )
+
+        self.memory.add_backer(0, bytes(self._image_vmem))
+        self.mapped_base = self.linked_base = 0
+        self.pic = True
+
+        self._add_defined_symbols()
+        self._add_relocs()
+
+        # FIXME: Expose __imp_* symbols through self.imports
+
+    def _add_defined_symbols(self) -> None:
+        for sym_name, sym_idx in self._coff.symbol_name_to_idx.items():
+            sym = self._coff.symbols[sym_idx]
+            if sym.SectionNumber > 0 and sym.StorageClass in {
+                IMAGE_SYM_CLASS.STATIC,
+                IMAGE_SYM_CLASS.LABEL,
+                IMAGE_SYM_CLASS.EXTERNAL,
+            }:
+                self.symbols.add(self.get_symbol(sym_name))
+
+    def _add_relocs(self) -> None:
+        for section_idx, section in enumerate(self._coff.sections):
+            for reloc in self._coff.relocations[section_idx]:
+                sym = self._coff.symbols[reloc.SymbolTableIndex]
+                sym_name = self._coff.get_symbol_name(reloc.SymbolTableIndex)
+                patch_offset = section.PointerToRawData + reloc.VirtualAddress
+
+                if sym.StorageClass in {
+                    IMAGE_SYM_CLASS.STATIC,
+                    IMAGE_SYM_CLASS.LABEL,
+                    IMAGE_SYM_CLASS.EXTERNAL,
+                }:
+                    reloc_class = RELOC_CLASSES[self._coff.header.Machine].get(reloc.Type, None)
+                    if reloc_class is not None:
+                        cle_symbol = self.get_symbol(sym_name, produce_extern_symbols=True)
+                        self.relocs.append(reloc_class(self, cle_symbol, patch_offset))
+                        continue
+
+                log.warning("Skipped relocation type %#x at %#x for symbol %s", reloc.Type, patch_offset, sym_name)
+
+    @staticmethod
+    def is_compatible(stream):
+        stream.seek(0)
+        identstring = stream.read(2)
+        stream.seek(0)
+        return int.from_bytes(identstring, "little") in (IMAGE_FILE_MACHINE.I386, IMAGE_FILE_MACHINE.AMD64)
+
+    def get_symbol(self, name: str, produce_extern_symbols: bool = False) -> Optional[Symbol]:
+        if name not in self._coff.symbol_name_to_idx:
+            return None
+
+        if name == "__ImageBase":
+            return Symbol(self, name, 0, 0, SymbolType.TYPE_OTHER)
+
+        sym = self._coff.symbols[self._coff.symbol_name_to_idx[name]]
+        if sym.StorageClass in {
+            IMAGE_SYM_CLASS.STATIC,
+            IMAGE_SYM_CLASS.LABEL,
+            IMAGE_SYM_CLASS.EXTERNAL,
+        }:
+            symbol_type = SymbolType.TYPE_FUNCTION if sym.Type == 0x20 else SymbolType.TYPE_OTHER
+            if sym.SectionNumber > 0:
+                sym_addr = self._coff.sections[sym.SectionNumber - 1].PointerToRawData + sym.Value
+                return Symbol(self, name, sym_addr, 1, symbol_type)
+            elif sym.SectionNumber == 0:
+                if produce_extern_symbols:
+                    return Symbol(self, name, 0, sym.Value, symbol_type)
+                return None
+
+        raise NotImplementedError("Unsupported symbol")
+
+
+register_backend("COFF", Coff)
diff --git a/tests/test_coff.py b/tests/test_coff.py
new file mode 100644
index 00000000..4aefb6e0
--- /dev/null
+++ b/tests/test_coff.py
@@ -0,0 +1,36 @@
+# pylint:disable=no-self-use
+
+import os
+import unittest
+
+import cle
+
+TEST_BASE = os.path.join(os.path.dirname(os.path.realpath(__file__)), os.path.join("..", "..", "binaries"))
+
+
+class TestCoff(unittest.TestCase):
+    """
+    Test COFF loader.
+    """
+
+    def test_x86(self):
+        exe = os.path.join(TEST_BASE, "tests", "x86", "fauxware.obj")
+        ld = cle.Loader(exe)
+        symbol_names = {sym.name for sym in ld.main_object.symbols}
+        assert "_main" in symbol_names
+        assert "_accepted" in symbol_names
+        assert "_rejected" in symbol_names
+        assert "_authenticate" in symbol_names
+
+    def test_x86_64(self):
+        exe = os.path.join(TEST_BASE, "tests", "x86_64", "fauxware.obj")
+        ld = cle.Loader(exe)
+        symbol_names = {sym.name for sym in ld.main_object.symbols}
+        assert "main" in symbol_names
+        assert "accepted" in symbol_names
+        assert "rejected" in symbol_names
+        assert "authenticate" in symbol_names
+
+
+if __name__ == "__main__":
+    unittest.main()