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Diffstat (limited to 'contrib/devtools/pixie.py')
| -rw-r--r-- | contrib/devtools/pixie.py | 323 |
1 files changed, 323 insertions, 0 deletions
diff --git a/contrib/devtools/pixie.py b/contrib/devtools/pixie.py new file mode 100644 index 0000000000..8cf06a799a --- /dev/null +++ b/contrib/devtools/pixie.py @@ -0,0 +1,323 @@ +#!/usr/bin/env python3 +# Copyright (c) 2020 Wladimir J. van der Laan +# Distributed under the MIT software license, see the accompanying +# file COPYING or http://www.opensource.org/licenses/mit-license.php. +''' +Compact, self-contained ELF implementation for bitcoin-core security checks. +''' +import struct +import types +from typing import Dict, List, Optional, Union, Tuple + +# you can find all these values in elf.h +EI_NIDENT = 16 + +# Byte indices in e_ident +EI_CLASS = 4 # ELFCLASSxx +EI_DATA = 5 # ELFDATAxxxx + +ELFCLASS32 = 1 # 32-bit +ELFCLASS64 = 2 # 64-bit + +ELFDATA2LSB = 1 # little endian +ELFDATA2MSB = 2 # big endian + +# relevant values for e_machine +EM_386 = 3 +EM_PPC64 = 21 +EM_ARM = 40 +EM_AARCH64 = 183 +EM_X86_64 = 62 +EM_RISCV = 243 + +# relevant values for e_type +ET_DYN = 3 + +# relevant values for sh_type +SHT_PROGBITS = 1 +SHT_STRTAB = 3 +SHT_DYNAMIC = 6 +SHT_DYNSYM = 11 +SHT_GNU_verneed = 0x6ffffffe +SHT_GNU_versym = 0x6fffffff + +# relevant values for p_type +PT_LOAD = 1 +PT_GNU_STACK = 0x6474e551 +PT_GNU_RELRO = 0x6474e552 + +# relevant values for p_flags +PF_X = (1 << 0) +PF_W = (1 << 1) +PF_R = (1 << 2) + +# relevant values for d_tag +DT_NEEDED = 1 +DT_FLAGS = 30 + +# relevant values of `d_un.d_val' in the DT_FLAGS entry +DF_BIND_NOW = 0x00000008 + +# relevant d_tags with string payload +STRING_TAGS = {DT_NEEDED} + +# rrlevant values for ST_BIND subfield of st_info (symbol binding) +STB_LOCAL = 0 + +class ELFRecord(types.SimpleNamespace): + '''Unified parsing for ELF records.''' + def __init__(self, data: bytes, offset: int, eh: 'ELFHeader', total_size: Optional[int]) -> None: + hdr_struct = self.STRUCT[eh.ei_class][0][eh.ei_data] + if total_size is not None and hdr_struct.size > total_size: + raise ValueError(f'{self.__class__.__name__} header size too small ({total_size} < {hdr_struct.size})') + for field, value in zip(self.STRUCT[eh.ei_class][1], hdr_struct.unpack(data[offset:offset + hdr_struct.size])): + setattr(self, field, value) + +def BiStruct(chars: str) -> Dict[int, struct.Struct]: + '''Compile a struct parser for both endians.''' + return { + ELFDATA2LSB: struct.Struct('<' + chars), + ELFDATA2MSB: struct.Struct('>' + chars), + } + +class ELFHeader(ELFRecord): + FIELDS = ['e_type', 'e_machine', 'e_version', 'e_entry', 'e_phoff', 'e_shoff', 'e_flags', 'e_ehsize', 'e_phentsize', 'e_phnum', 'e_shentsize', 'e_shnum', 'e_shstrndx'] + STRUCT = { + ELFCLASS32: (BiStruct('HHIIIIIHHHHHH'), FIELDS), + ELFCLASS64: (BiStruct('HHIQQQIHHHHHH'), FIELDS), + } + + def __init__(self, data: bytes, offset: int) -> None: + self.e_ident = data[offset:offset + EI_NIDENT] + if self.e_ident[0:4] != b'\x7fELF': + raise ValueError('invalid ELF magic') + self.ei_class = self.e_ident[EI_CLASS] + self.ei_data = self.e_ident[EI_DATA] + + super().__init__(data, offset + EI_NIDENT, self, None) + + def __repr__(self) -> str: + return f'Header(e_ident={self.e_ident!r}, e_type={self.e_type}, e_machine={self.e_machine}, e_version={self.e_version}, e_entry={self.e_entry}, e_phoff={self.e_phoff}, e_shoff={self.e_shoff}, e_flags={self.e_flags}, e_ehsize={self.e_ehsize}, e_phentsize={self.e_phentsize}, e_phnum={self.e_phnum}, e_shentsize={self.e_shentsize}, e_shnum={self.e_shnum}, e_shstrndx={self.e_shstrndx})' + +class Section(ELFRecord): + name: Optional[bytes] = None + FIELDS = ['sh_name', 'sh_type', 'sh_flags', 'sh_addr', 'sh_offset', 'sh_size', 'sh_link', 'sh_info', 'sh_addralign', 'sh_entsize'] + STRUCT = { + ELFCLASS32: (BiStruct('IIIIIIIIII'), FIELDS), + ELFCLASS64: (BiStruct('IIQQQQIIQQ'), FIELDS), + } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None: + super().__init__(data, offset, eh, eh.e_shentsize) + self._data = data + + def __repr__(self) -> str: + return f'Section(sh_name={self.sh_name}({self.name!r}), sh_type=0x{self.sh_type:x}, sh_flags={self.sh_flags}, sh_addr=0x{self.sh_addr:x}, sh_offset=0x{self.sh_offset:x}, sh_size={self.sh_size}, sh_link={self.sh_link}, sh_info={self.sh_info}, sh_addralign={self.sh_addralign}, sh_entsize={self.sh_entsize})' + + def contents(self) -> bytes: + '''Return section contents.''' + return self._data[self.sh_offset:self.sh_offset + self.sh_size] + +class ProgramHeader(ELFRecord): + STRUCT = { + # different ELF classes have the same fields, but in a different order to optimize space versus alignment + ELFCLASS32: (BiStruct('IIIIIIII'), ['p_type', 'p_offset', 'p_vaddr', 'p_paddr', 'p_filesz', 'p_memsz', 'p_flags', 'p_align']), + ELFCLASS64: (BiStruct('IIQQQQQQ'), ['p_type', 'p_flags', 'p_offset', 'p_vaddr', 'p_paddr', 'p_filesz', 'p_memsz', 'p_align']), + } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None: + super().__init__(data, offset, eh, eh.e_phentsize) + + def __repr__(self) -> str: + return f'ProgramHeader(p_type={self.p_type}, p_offset={self.p_offset}, p_vaddr={self.p_vaddr}, p_paddr={self.p_paddr}, p_filesz={self.p_filesz}, p_memsz={self.p_memsz}, p_flags={self.p_flags}, p_align={self.p_align})' + +class Symbol(ELFRecord): + STRUCT = { + # different ELF classes have the same fields, but in a different order to optimize space versus alignment + ELFCLASS32: (BiStruct('IIIBBH'), ['st_name', 'st_value', 'st_size', 'st_info', 'st_other', 'st_shndx']), + ELFCLASS64: (BiStruct('IBBHQQ'), ['st_name', 'st_info', 'st_other', 'st_shndx', 'st_value', 'st_size']), + } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader, symtab: Section, strings: bytes, version: Optional[bytes]) -> None: + super().__init__(data, offset, eh, symtab.sh_entsize) + self.name = _lookup_string(strings, self.st_name) + self.version = version + + def __repr__(self) -> str: + return f'Symbol(st_name={self.st_name}({self.name!r}), st_value={self.st_value}, st_size={self.st_size}, st_info={self.st_info}, st_other={self.st_other}, st_shndx={self.st_shndx}, version={self.version!r})' + + @property + def is_import(self) -> bool: + '''Returns whether the symbol is an imported symbol.''' + return self.st_bind != STB_LOCAL and self.st_shndx == 0 + + @property + def is_export(self) -> bool: + '''Returns whether the symbol is an exported symbol.''' + return self.st_bind != STB_LOCAL and self.st_shndx != 0 + + @property + def st_bind(self) -> int: + '''Returns STB_*.''' + return self.st_info >> 4 + +class Verneed(ELFRecord): + DEF = (BiStruct('HHIII'), ['vn_version', 'vn_cnt', 'vn_file', 'vn_aux', 'vn_next']) + STRUCT = { ELFCLASS32: DEF, ELFCLASS64: DEF } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None: + super().__init__(data, offset, eh, None) + + def __repr__(self) -> str: + return f'Verneed(vn_version={self.vn_version}, vn_cnt={self.vn_cnt}, vn_file={self.vn_file}, vn_aux={self.vn_aux}, vn_next={self.vn_next})' + +class Vernaux(ELFRecord): + DEF = (BiStruct('IHHII'), ['vna_hash', 'vna_flags', 'vna_other', 'vna_name', 'vna_next']) + STRUCT = { ELFCLASS32: DEF, ELFCLASS64: DEF } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader, strings: bytes) -> None: + super().__init__(data, offset, eh, None) + self.name = _lookup_string(strings, self.vna_name) + + def __repr__(self) -> str: + return f'Veraux(vna_hash={self.vna_hash}, vna_flags={self.vna_flags}, vna_other={self.vna_other}, vna_name={self.vna_name}({self.name!r}), vna_next={self.vna_next})' + +class DynTag(ELFRecord): + STRUCT = { + ELFCLASS32: (BiStruct('II'), ['d_tag', 'd_val']), + ELFCLASS64: (BiStruct('QQ'), ['d_tag', 'd_val']), + } + + def __init__(self, data: bytes, offset: int, eh: ELFHeader, section: Section) -> None: + super().__init__(data, offset, eh, section.sh_entsize) + + def __repr__(self) -> str: + return f'DynTag(d_tag={self.d_tag}, d_val={self.d_val})' + +def _lookup_string(data: bytes, index: int) -> bytes: + '''Look up string by offset in ELF string table.''' + endx = data.find(b'\x00', index) + assert endx != -1 + return data[index:endx] + +VERSYM_S = BiStruct('H') # .gnu_version section has a single 16-bit integer per symbol in the linked section +def _parse_symbol_table(section: Section, strings: bytes, eh: ELFHeader, versym: bytes, verneed: Dict[int, bytes]) -> List[Symbol]: + '''Parse symbol table, return a list of symbols.''' + data = section.contents() + symbols = [] + versym_iter = (verneed.get(v[0]) for v in VERSYM_S[eh.ei_data].iter_unpack(versym)) + for ofs, version in zip(range(0, len(data), section.sh_entsize), versym_iter): + symbols.append(Symbol(data, ofs, eh, section, strings, version)) + return symbols + +def _parse_verneed(section: Section, strings: bytes, eh: ELFHeader) -> Dict[int, bytes]: + '''Parse .gnu.version_r section, return a dictionary of {versym: 'GLIBC_...'}.''' + data = section.contents() + ofs = 0 + result = {} + while True: + verneed = Verneed(data, ofs, eh) + aofs = verneed.vn_aux + while True: + vernaux = Vernaux(data, aofs, eh, strings) + result[vernaux.vna_other] = vernaux.name + if not vernaux.vna_next: + break + aofs += vernaux.vna_next + + if not verneed.vn_next: + break + ofs += verneed.vn_next + + return result + +def _parse_dyn_tags(section: Section, strings: bytes, eh: ELFHeader) -> List[Tuple[int, Union[bytes, int]]]: + '''Parse dynamic tags. Return array of tuples.''' + data = section.contents() + ofs = 0 + result = [] + for ofs in range(0, len(data), section.sh_entsize): + tag = DynTag(data, ofs, eh, section) + val = _lookup_string(strings, tag.d_val) if tag.d_tag in STRING_TAGS else tag.d_val + result.append((tag.d_tag, val)) + + return result + +class ELFFile: + sections: List[Section] + program_headers: List[ProgramHeader] + dyn_symbols: List[Symbol] + dyn_tags: List[Tuple[int, Union[bytes, int]]] + + def __init__(self, data: bytes) -> None: + self.data = data + self.hdr = ELFHeader(self.data, 0) + self._load_sections() + self._load_program_headers() + self._load_dyn_symbols() + self._load_dyn_tags() + self._section_to_segment_mapping() + + def _load_sections(self) -> None: + self.sections = [] + for idx in range(self.hdr.e_shnum): + offset = self.hdr.e_shoff + idx * self.hdr.e_shentsize + self.sections.append(Section(self.data, offset, self.hdr)) + + shstr = self.sections[self.hdr.e_shstrndx].contents() + for section in self.sections: + section.name = _lookup_string(shstr, section.sh_name) + + def _load_program_headers(self) -> None: + self.program_headers = [] + for idx in range(self.hdr.e_phnum): + offset = self.hdr.e_phoff + idx * self.hdr.e_phentsize + self.program_headers.append(ProgramHeader(self.data, offset, self.hdr)) + + def _load_dyn_symbols(self) -> None: + # first, load 'verneed' section + verneed = None + for section in self.sections: + if section.sh_type == SHT_GNU_verneed: + strtab = self.sections[section.sh_link].contents() # associated string table + assert verneed is None # only one section of this kind please + verneed = _parse_verneed(section, strtab, self.hdr) + assert verneed is not None + + # then, correlate GNU versym sections with dynamic symbol sections + versym = {} + for section in self.sections: + if section.sh_type == SHT_GNU_versym: + versym[section.sh_link] = section + + # finally, load dynsym sections + self.dyn_symbols = [] + for idx, section in enumerate(self.sections): + if section.sh_type == SHT_DYNSYM: # find dynamic symbol tables + strtab_data = self.sections[section.sh_link].contents() # associated string table + versym_data = versym[idx].contents() # associated symbol version table + self.dyn_symbols += _parse_symbol_table(section, strtab_data, self.hdr, versym_data, verneed) + + def _load_dyn_tags(self) -> None: + self.dyn_tags = [] + for idx, section in enumerate(self.sections): + if section.sh_type == SHT_DYNAMIC: # find dynamic tag tables + strtab = self.sections[section.sh_link].contents() # associated string table + self.dyn_tags += _parse_dyn_tags(section, strtab, self.hdr) + + def _section_to_segment_mapping(self) -> None: + for ph in self.program_headers: + ph.sections = [] + for section in self.sections: + if ph.p_vaddr <= section.sh_addr < (ph.p_vaddr + ph.p_memsz): + ph.sections.append(section) + + def query_dyn_tags(self, tag_in: int) -> List[Union[int, bytes]]: + '''Return the values of all dyn tags with the specified tag.''' + return [val for (tag, val) in self.dyn_tags if tag == tag_in] + + +def load(filename: str) -> ELFFile: + with open(filename, 'rb') as f: + data = f.read() + return ELFFile(data) |