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78 lines
3.1 KiB
78 lines
3.1 KiB
5 years ago
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#-------------------------------------------------------------------------------
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# elftools: elf/hash.py
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#
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# ELF hash table sections
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#
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# Andreas Ziegler (andreas.ziegler@fau.de)
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# This code is in the public domain
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#-------------------------------------------------------------------------------
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from ..common.utils import struct_parse
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class HashSection(object):
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""" Minimal part of an ELF hash section to find the number of symbols in the
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symbol table - useful for super-stripped binaries without section
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headers where only the start of the symbol table is known from the
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dynamic segment. The layout and contents are nicely described at
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https://flapenguin.me/2017/04/24/elf-lookup-dt-hash/.
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"""
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def __init__(self, stream, offset, elffile):
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self._stream = stream
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self._offset = offset
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self._elffile = elffile
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self.params = struct_parse(self._elffile.structs.Elf_Hash,
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self._stream,
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self._offset)
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def get_number_of_symbols(self):
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""" Get the number of symbols from the hash table parameters.
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"""
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return self.params['nchains']
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class GNUHashSection(object):
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""" Minimal part of a GNU hash section to find the number of symbols in the
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symbol table - useful for super-stripped binaries without section
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headers where only the start of the symbol table is known from the
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dynamic segment. The layout and contents are nicely described at
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https://flapenguin.me/2017/05/10/elf-lookup-dt-gnu-hash/.
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"""
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def __init__(self, stream, offset, elffile):
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self._stream = stream
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self._offset = offset
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self._elffile = elffile
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self.params = struct_parse(self._elffile.structs.Gnu_Hash,
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self._stream,
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self._offset)
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def get_number_of_symbols(self):
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""" Get the number of symbols in the hash table by finding the bucket
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with the highest symbol index and walking to the end of its chain.
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"""
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# Element sizes in the hash table
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wordsize = self._elffile.structs.Elf_word('').sizeof()
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xwordsize = self._elffile.structs.Elf_xword('').sizeof()
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# Find highest index in buckets array
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max_idx = max(self.params['buckets'])
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if max_idx < self.params['symoffset']:
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return self.params['symoffset']
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# Position the stream at the start of the corresponding chain
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chain_pos = self._offset + 4 * wordsize + \
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self.params['bloom_size'] * xwordsize + \
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self.params['nbuckets'] * wordsize + \
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(max_idx - self.params['symoffset']) * wordsize
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# Walk the chain to its end (lowest bit is set)
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while True:
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cur_hash = struct_parse(self._elffile.structs.Elf_word('elem'),
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self._stream,
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chain_pos)
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if cur_hash & 1:
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return max_idx + 1
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max_idx += 1
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chain_pos += wordsize
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