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109 lines
3.2 KiB
109 lines
3.2 KiB
7 months ago
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"""
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ELF file parser.
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This provides a class ``ELFFile`` that parses an ELF executable in a similar
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interface to ``ZipFile``. Only the read interface is implemented.
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Based on: https://gist.github.com/lyssdod/f51579ae8d93c8657a5564aefc2ffbca
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ELF header: https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html
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"""
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import enum
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import os
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import struct
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from typing import IO, Optional, Tuple
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class ELFInvalid(ValueError):
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pass
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class EIClass(enum.IntEnum):
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C32 = 1
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C64 = 2
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class EIData(enum.IntEnum):
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Lsb = 1
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Msb = 2
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class EMachine(enum.IntEnum):
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I386 = 3
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S390 = 22
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Arm = 40
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X8664 = 62
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AArc64 = 183
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class ELFFile:
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"""
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Representation of an ELF executable.
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"""
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def __init__(self, f: IO[bytes]) -> None:
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self._f = f
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try:
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ident = self._read("16B")
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except struct.error:
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raise ELFInvalid("unable to parse identification")
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magic = bytes(ident[:4])
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if magic != b"\x7fELF":
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raise ELFInvalid(f"invalid magic: {magic!r}")
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self.capacity = ident[4] # Format for program header (bitness).
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self.encoding = ident[5] # Data structure encoding (endianness).
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try:
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# e_fmt: Format for program header.
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# p_fmt: Format for section header.
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# p_idx: Indexes to find p_type, p_offset, and p_filesz.
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e_fmt, self._p_fmt, self._p_idx = {
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(1, 1): ("<HHIIIIIHHH", "<IIIIIIII", (0, 1, 4)), # 32-bit LSB.
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(1, 2): (">HHIIIIIHHH", ">IIIIIIII", (0, 1, 4)), # 32-bit MSB.
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(2, 1): ("<HHIQQQIHHH", "<IIQQQQQQ", (0, 2, 5)), # 64-bit LSB.
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(2, 2): (">HHIQQQIHHH", ">IIQQQQQQ", (0, 2, 5)), # 64-bit MSB.
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}[(self.capacity, self.encoding)]
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except KeyError:
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raise ELFInvalid(
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f"unrecognized capacity ({self.capacity}) or "
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f"encoding ({self.encoding})"
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)
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try:
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(
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_,
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self.machine, # Architecture type.
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_,
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_,
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self._e_phoff, # Offset of program header.
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_,
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self.flags, # Processor-specific flags.
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_,
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self._e_phentsize, # Size of section.
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self._e_phnum, # Number of sections.
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) = self._read(e_fmt)
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except struct.error as e:
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raise ELFInvalid("unable to parse machine and section information") from e
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def _read(self, fmt: str) -> Tuple[int, ...]:
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return struct.unpack(fmt, self._f.read(struct.calcsize(fmt)))
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@property
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def interpreter(self) -> Optional[str]:
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"""
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The path recorded in the ``PT_INTERP`` section header.
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"""
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for index in range(self._e_phnum):
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self._f.seek(self._e_phoff + self._e_phentsize * index)
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try:
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data = self._read(self._p_fmt)
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except struct.error:
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continue
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if data[self._p_idx[0]] != 3: # Not PT_INTERP.
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continue
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self._f.seek(data[self._p_idx[1]])
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return os.fsdecode(self._f.read(data[self._p_idx[2]])).strip("\0")
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return None
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