144 lines
5.4 KiB
Python
144 lines
5.4 KiB
Python
#-------------------------------------------------------------------------------
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# elftools: elf/segments.py
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#
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# ELF segments
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#
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# Eli Bendersky (eliben@gmail.com)
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# This code is in the public domain
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#-------------------------------------------------------------------------------
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from __future__ import annotations
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from typing import IO, TYPE_CHECKING, Any, Literal, overload
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from ..construct import CString
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from ..common.utils import struct_parse
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from .constants import SH_FLAGS
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from .notes import iter_notes
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if TYPE_CHECKING:
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from collections.abc import Iterator
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from ..construct import Container
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from .elffile import ELFFile
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from .sections import Section
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class Segment:
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def __init__(self, header: Container, stream: IO[bytes]) -> None:
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self.header = header
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self.stream = stream
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def data(self) -> bytes:
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""" The segment data from the file.
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"""
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self.stream.seek(self['p_offset'])
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return self.stream.read(self['p_filesz'])
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@overload
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def __getitem__(self, name: Literal["p_filesz", "p_memsz", "p_offset", "p_vaddr"]) -> int: ...
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@overload
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def __getitem__(self, name: Literal["p_type"]) -> str: ...
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@overload
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def __getitem__(self, name: str) -> Any: ...
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def __getitem__(self, name: str) -> Any:
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""" Implement dict-like access to header entries
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"""
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return self.header[name]
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def section_in_segment(self, section: Section) -> bool:
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""" Is the given section contained in this segment?
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Note: this tries to reproduce the intricate rules of the
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ELF_SECTION_IN_SEGMENT_STRICT macro of the header
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elf/include/internal.h in the source of binutils.
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"""
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# Only the 'strict' checks from ELF_SECTION_IN_SEGMENT_1 are included
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segtype: str = self['p_type']
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sectype: str = section['sh_type']
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secflags: int = section['sh_flags']
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# Only PT_LOAD, PT_GNU_RELRO and PT_TLS segments can contain SHF_TLS
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# sections
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if ( secflags & SH_FLAGS.SHF_TLS and
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segtype in ('PT_TLS', 'PT_GNU_RELRO', 'PT_LOAD')):
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pass
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# PT_TLS segment contains only SHF_TLS sections, PT_PHDR no sections
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# at all
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elif ( (secflags & SH_FLAGS.SHF_TLS) == 0 and
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segtype not in ('PT_TLS', 'PT_PHDR')):
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pass
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else:
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return False
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# PT_LOAD and similar segments only have SHF_ALLOC sections.
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if ( (secflags & SH_FLAGS.SHF_ALLOC) == 0 and
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segtype in ('PT_LOAD', 'PT_DYNAMIC', 'PT_GNU_EH_FRAME',
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'PT_GNU_RELRO', 'PT_GNU_STACK')):
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return False
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# In ELF_SECTION_IN_SEGMENT_STRICT the flag check_vma is on, so if
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# this is an alloc section, check whether its VMA is in bounds.
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if secflags & SH_FLAGS.SHF_ALLOC:
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secaddr: int = section['sh_addr']
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vaddr: int = self['p_vaddr']
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# This checks that the section is wholly contained in the segment.
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# The third condition is the 'strict' one - an empty section will
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# not match at the very end of the segment (unless the segment is
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# also zero size, which is handled by the second condition).
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# Seva 2024-07-12: a zero length section at a zero offset
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# in a zero length segment should match - in GNU readelf, p_memsz
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# is unsigned, on a zero length segment p_memsz-1 wraps around
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# and the third condition matches.
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if not (secaddr >= vaddr and
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secaddr - vaddr + section['sh_size'] <= self['p_memsz'] and
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(self['p_memsz'] == 0 or secaddr - vaddr <= self['p_memsz'] - 1)):
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return False
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# If we've come this far and it's a NOBITS section, it's in the segment
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if sectype == 'SHT_NOBITS':
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return True
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secoffset: int = section['sh_offset']
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poffset: int = self['p_offset']
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# Same logic as with secaddr vs. vaddr checks above, just on offsets in
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# the file
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# Seva 2024-07-12: similar discrepancy with readelf from unsignedness of p_filesz
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return (secoffset >= poffset and
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secoffset - poffset + section['sh_size'] <= self['p_filesz'] and
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(self['p_filesz'] == 0 or secoffset - poffset <= self['p_filesz'] - 1))
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class InterpSegment(Segment):
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""" INTERP segment. Knows how to obtain the path to the interpreter used
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for this ELF file.
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"""
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def __init__(self, header: Container, stream: IO[bytes]) -> None:
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super().__init__(header, stream)
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def get_interp_name(self) -> str:
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""" Obtain the interpreter path used for this ELF file.
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"""
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path_offset: int = self['p_offset']
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return struct_parse(
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CString('', encoding='utf-8'),
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self.stream,
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stream_pos=path_offset)
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class NoteSegment(Segment):
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""" NOTE segment. Knows how to parse notes.
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"""
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def __init__(self, header: Container, stream: IO[bytes], elffile: ELFFile) -> None:
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super().__init__(header, stream)
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self.elffile = elffile
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def iter_notes(self) -> Iterator[Container]:
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""" Yield all the notes in the segment. Each result is a dictionary-
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like object with "n_name", "n_type", and "n_desc" fields, amongst
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others.
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"""
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return iter_notes(self.elffile, self['p_offset'], self['p_filesz'])
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