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| """Convert an ELF64 PIE OEP memory dump back to file-time state."""
import argparse
import os
import struct
from pathlib import Path
PT_LOAD = 1
PT_DYNAMIC = 2
DT_NULL = 0
DT_DEBUG = 21
DT_RELA = 7
DT_RELASZ = 8
DT_RELAENT = 9
DT_JMPREL = 23
DT_PLTRELSZ = 2
R_X86_64_GLOB_DAT = 6
R_X86_64_JUMP_SLOT = 7
R_X86_64_RELATIVE = 8
DYNAMIC_POINTER_TAGS = {
3,
4,
5,
6,
7,
12,
13,
17,
23,
25,
26,
32,
0x6FFFFEF5,
0x6FFFFFF0,
0x6FFFFFFC,
0x6FFFFFFE,
}
def parse_program_headers(data):
if data[:6] != b"\x7fELF\x02\x01":
raise ValueError("input is not a little-endian ELF64 file")
phoff = struct.unpack_from("<Q", data, 0x20)[0]
phentsize = struct.unpack_from("<H", data, 0x36)[0]
phnum = struct.unpack_from("<H", data, 0x38)[0]
if phentsize < 0x38 or not 0 < phnum < 0x1000:
raise ValueError("invalid program header table")
return [
struct.unpack_from("<IIQQQQQQ", data, phoff + i * phentsize)
for i in range(phnum)
]
def vaddr_to_offset(loads, vaddr, size=1):
for ph in loads:
file_offset, segment_vaddr, filesz = ph[2], ph[3], ph[5]
if segment_vaddr <= vaddr and vaddr + size <= segment_vaddr + filesz:
return file_offset + vaddr - segment_vaddr
raise ValueError("virtual address 0x%x is not file-backed" % vaddr)
def repair_dynamic(data, phdrs, old_base):
loads = [ph for ph in phdrs if ph[0] == PT_LOAD]
image_min = min(ph[3] for ph in loads)
image_max = max(ph[3] + ph[6] for ph in loads)
runtime_min = old_base + image_min
runtime_max = old_base + image_max
dynamic = next((ph for ph in phdrs if ph[0] == PT_DYNAMIC), None)
if dynamic is None:
raise ValueError("ELF has no PT_DYNAMIC")
dynamic_offset = vaddr_to_offset(loads, dynamic[3], dynamic[5])
values = {}
changes = []
for relative in range(0, dynamic[5], 16):
offset = dynamic_offset + relative
tag, value = struct.unpack_from("<QQ", data, offset)
if tag == DT_NULL:
break
repaired = value
reason = None
if tag == DT_DEBUG and value != 0:
repaired = 0
reason = "clear DT_DEBUG"
elif tag in DYNAMIC_POINTER_TAGS and runtime_min <= value < runtime_max:
repaired = value - old_base
reason = "remove old load bias from dynamic pointer"
if repaired != value:
struct.pack_into("<Q", data, offset + 8, repaired)
changes.append((offset + 8, value, repaired, reason))
values[tag] = repaired
return loads, values, changes
def iter_rela(data, loads, vaddr, size, entry_size):
if entry_size < 24 or size % entry_size:
raise ValueError("invalid ELF64 RELA table")
offset = vaddr_to_offset(loads, vaddr, size)
for relative in range(0, size, entry_size):
yield struct.unpack_from("<QQq", data, offset + relative)
def repair_relocation_targets(data, loads, dynamic):
rela_vaddr = dynamic.get(DT_RELA)
rela_size = dynamic.get(DT_RELASZ, 0)
rela_entry = dynamic.get(DT_RELAENT, 24)
if rela_vaddr is None:
raise ValueError("ELF has no DT_RELA")
relocations = list(iter_rela(data, loads, rela_vaddr, rela_size, rela_entry))
jmprel_vaddr = dynamic.get(DT_JMPREL)
jmprel_size = dynamic.get(DT_PLTRELSZ, 0)
if jmprel_vaddr is not None and jmprel_size:
relocations.extend(
iter_rela(data, loads, jmprel_vaddr, jmprel_size, rela_entry)
)
changes = []
for r_offset, r_info, r_addend in relocations:
relocation_type = r_info & 0xFFFFFFFF
try:
target = vaddr_to_offset(loads, r_offset, 8)
except ValueError:
continue
current = struct.unpack_from("<Q", data, target)[0]
if relocation_type == R_X86_64_RELATIVE:
repaired = r_addend & 0xFFFFFFFFFFFFFFFF
reason = "restore R_X86_64_RELATIVE addend"
elif relocation_type in (R_X86_64_GLOB_DAT, R_X86_64_JUMP_SLOT):
repaired = 0
reason = "clear resolved symbol slot"
else:
continue
if repaired != current:
struct.pack_into("<Q", data, target, repaired)
changes.append((target, current, repaired, reason))
return changes
def repair(input_path, output_path, old_base):
data = bytearray(Path(input_path).read_bytes())
phdrs = parse_program_headers(data)
loads, dynamic, dynamic_changes = repair_dynamic(data, phdrs, old_base)
relocation_changes = repair_relocation_targets(data, loads, dynamic)
Path(output_path).write_bytes(data)
os.chmod(output_path, 0o755)
for offset, old, new, reason in dynamic_changes + relocation_changes:
print("0x%04x: 0x%x -> 0x%x (%s)" % (offset, old, new, reason))
print(
"wrote %s: %d dynamic fixes, %d relocation-target fixes"
% (output_path, len(dynamic_changes), len(relocation_changes))
)
def main():
parser = argparse.ArgumentParser()
parser.add_argument("input")
parser.add_argument("output")
parser.add_argument(
"old_base",
type=lambda value: int(value, 0),
help="load bias of the process from which the OEP dump was taken",
)
args = parser.parse_args()
repair(args.input, args.output, args.old_base)
if __name__ == "__main__":
main()
|
