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kfinder.py
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kfinder.py
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#
# Simple POC to retrive kernel symbols from a
# physical memory dump.
#
# Mariano Graziano - graziano@eurecom.fr
#
#
# References:
# - https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-4.md
# - Linux kernel source code
# - https://github.com/psviderski/volatility-android/blob/master/volatility/plugins/linux/auto_ksymbol.py
#
# The last link is basically the same idea/approach applied to Android. I discovered it
# few days ago. Really cool work, it's a pity his thesis is not available in
# english (only in russian).
#
# Thanks:
# Andrew Case and Enrico Perla
#
#
# XXD Manual Debugging:
#
# cat System.map-3.2.0-23-generic-pae | grep -i dns_query
# c1574e30 T dns_query
# c17d0fc0 r __ksymtab_dns_query
# c17dc4ec r __kcrctab_dns_query
# c17fde42 r __kstrtab_dns_query
#
# 21:42:06 emdel -> xxd kernelexp.ram | grep -ni dns_query -A 1 -B 1
# 1450737-1622f00: 6174 6500 646e 735f 7265 736f 6c76 6572 ate.dns_resolver
# 1450738:1622f10: 2e64 6562 7567 0064 6e73 5f71 7565 7279 .debug.dns_query
# 1450739-1622f20: 0000 0000 0000 00c1 0000 00c1 db00 00c1 ................
#--
# 1572324-17fde30: 5f6e 6574 5f73 7973 6374 6c5f 7461 626c _net_sysctl_tabl
# 1572325:17fde40: 6500 646e 735f 7175 6572 7900 6b6c 6973 e.dns_query.klis
# 1572326-17fde50: 745f 6e65 7874 006b 6c69 7374 5f69 7465 t_next.klist_ite
#
# c17fde42 --> 42de7fc1
#
# 21:44:25 emdel -> xxd kernelexp.ram | grep -ni "42de 7fc1"
# 1464144:16574f0: f0dd 7fc1 0cde 7fc1 28de 7fc1 42de 7fc1 ........(...B...
# 1560829:17d0fc0: [[304e 57c1]] 42de 7fc1 30e4 34c1 621c 7fc1 0NW.B...0.4.b...
#
import mmap, sys, struct, os, string
from collections import OrderedDict
PAGE_SIZE = 4096
ELF_MAGIC = 0x7F454C46
x64 = 0
x86 = 0
is_x86 = False
is_x64 = False
THRESHOLD = 20
ei_class_table = {
0x01: "32bit format",
0x02: "64bit format"
}
ei_osabi_table = {
0x00: "System V",
0x01: "HP-UX",
0x02: "NetBSD",
0x03: "Linix",
0x06: "Solaris",
0x07: "AIX",
0x08: "IRIX",
0x09: "FreeBSD",
0x0C: "OpenBSD",
0x0D: "OpenVMS",
0x0E: "NonStop Kernel",
0x0F: "AROS",
0x10: "Fenix OS",
0x11: "CloudABI",
0x53: "Sortix"
}
e_type_table = {
0x01: "relocatable",
0x02: "executable",
0x03: "shared",
0x04: "core"
}
e_machine_table = {
0x00: "No specific instruction set",
0x02: "SPARC",
0x03: "x86",
0x08: "MIPS",
0x14: "PowerPC",
0x28: "ARM",
0x2A: "SuperH",
0x32: "IA-64",
0x3E: "x86_64",
0xB7: "AArch64"
}
def lookup(m, ksymtab_pa, symbol_addr_raw):
for addr in xrange(ksymtab_pa, 0x3000000, 0x04):
m.seek(addr)
if is_x86:
raw = m.read(4)
elif is_x64:
raw = m.read(8)
if raw == symbol_addr_raw:
if is_x86:
symbol_offset = (addr - 4)
elif is_x64:
symbol_offset = (addr - 8)
if len(sys.argv) > 2:
print ":: symbol_va packed found at 0x%08x" % symbol_offset
m.seek(symbol_offset)
if is_x86:
addr_raw = m.read(4)
symbol_addr = struct.unpack("<L", addr_raw)[0]
elif is_x64:
addr_raw = m.read(8)
symbol_addr = struct.unpack("<Q", addr_raw)[0]
return symbol_addr
return None
def find_ksymtab_strings(m, start_addr, end_addr):
candidate_value = ""
ksymtab_strings = None
for page in range(start_addr, end_addr, PAGE_SIZE):
#print "\tPage: %x" % page
for addr in range(page, page + PAGE_SIZE - 1, 0x01):
m.seek(addr)
raw = m.read(1)
if raw != "\x00":
candidate_value += raw
continue
if "init_task" in candidate_value:
ksymtab_strings = addr
print ":: init_task found at offset: 0x%x" % addr
print ":: __ksymtab_strings found at offset: 0x%x" % (addr - len("init_task"))
return ksymtab_strings
candidate_value = ""
return None
def main():
global x64, x86, is_x64, is_x86
if len(sys.argv) < 2:
print "[-] Usage: %s %s %s" % (sys.argv[0], "<memory_dump>", "[symbol]")
sys.exit(1)
# Open the memory dump
try:
fd = os.open(sys.argv[1], os.O_RDONLY)
except:
print "[-] Error: fopen.\n"
sys.exit(1)
# mmap the dump
try:
m = mmap.mmap(fd, 0, mmap.MAP_PRIVATE, mmap.PROT_READ)
except:
print "[-] Error: memmap.\n"
sys.exit(1)
# Scan for ELF files and get the architecture
print "Size: " , m.size()
for page in range(0, m.size(), PAGE_SIZE):
m.seek(page)
raw = m.read(4)
value = struct.unpack(">L", raw)[0]
if value == ELF_MAGIC:
print "Page: %x" % page
raw = m.read(1)
ei_class = struct.unpack("<B", raw)[0]
try:
print "\t - ei_class: %s" % ei_class_table[ei_class]
except KeyError:
continue
m.seek(page + 0x07)
raw = m.read(1)
ei_osabi = struct.unpack("<B", raw)[0]
try:
print "\t - ABI: %s" % ei_osabi_table[ei_osabi]
except KeyError:
continue
m.seek(page + 0x10)
raw = m.read(2)
e_type = struct.unpack("<H", raw)[0]
try:
print "\t - e_type: %s" % e_type_table[e_type]
except KeyError:
continue
m.seek(page + 0x12)
raw = m.read(2)
e_machine = struct.unpack("<H", raw)[0]
try:
machine = e_machine_table[e_machine]
print "\t - e_machine %s" % machine
if machine == "x86_64":
x64 += 1
elif machine == "x86":
x86 += 1
except KeyError:
continue
if x64 > THRESHOLD and x86 > THRESHOLD:
print "Something went wrong."
os.close(fd)
m.close()
sys.exit(1)
elif x64 > THRESHOLD:
print "\n:: Architecture identified: x86_64"
is_x64 = True
elif x86 > THRESHOLD:
print "\n:: Architecture identified: x86"
is_x86 = True
if is_x86:
ksymtab_strings = find_ksymtab_strings(m, 0x01000000, 0x02000000)
elif is_x64:
ksymtab_strings = find_ksymtab_strings(m, 0x100000, 0x03000000)
if not ksymtab_strings:
print ":: __ksymtab_strings not found..."
os.close(fd)
m.close()
sys.exit(1)
symbol_names = OrderedDict()
# TODO: Make it modular
candidate_value = ""
prev_addr = 0
prev_val = ""
for addr in range(ksymtab_strings - len("init_task"), 0x03000000, 0x01):
m.seek(addr)
raw = m.read(1)
if raw != "\x00":
candidate_value += raw
continue
# Recursive mode. Build necessary data structures
kaddr = addr - (len(candidate_value) + 1)
if len(sys.argv) == 2:
final_check = string.ascii_letters + "_" + string.digits
if all(c in final_check for c in candidate_value) and len(candidate_value) >= 2:
if len(symbol_names.keys()) == 0:
symbol_names[hex(kaddr).strip("L")] = candidate_value
else:
if prev_addr in symbol_names.keys():
if hex(addr - (len(candidate_value) + 1) - (len(symbol_names[prev_addr]) + 1)).strip("L") in symbol_names.keys():
symbol_names[hex(kaddr).strip("L")] = candidate_value
# Single lookup mode
elif sys.argv[2] == candidate_value:
symbol_pa = addr - len(sys.argv[2])
print ":: Symbol %s found at offset: 0x%08x" % (sys.argv[2], symbol_pa)
#print len(candidate_value), len(sys.argv[2])
if is_x86:
symbol_va = symbol_pa + 0xC0000000
elif is_x64:
symbol_va = symbol_pa + 0xFFFFFFFF80000000
print ":: Symbol Virtual Address: 0x%08x" % symbol_va
break
prev_addr = hex(kaddr).strip("L")
prev_val = candidate_value
candidate_value = ""
# Single lookup mode
if len(sys.argv) > 2:
print ":: Packing the symbol_va"
if is_x86:
symbol_addr_raw = struct.pack("<L", symbol_va)
elif is_x64:
symbol_addr_raw = struct.pack("<Q", symbol_va)
ksymtab_pa = (ksymtab_strings - 0x100000) >> 2 << 2
print ":: __ksymtab offset guess: 0x%08x" % ksymtab_pa
symbol = lookup(m, ksymtab_pa, symbol_addr_raw)
print ":: %s at 0x%08x" % (sys.argv[2], symbol)
else:
system_map = OrderedDict()
print "[+] Retrived %d symbols" % len(symbol_names.keys())
print symbol_names
ksymtab_pa = (ksymtab_strings - 0x100000) >> 2 << 2
for k, v in symbol_names.items():
if is_x86:
symbol_va = (int(k, 16) + 1) + 0xC0000000
symbol_addr_raw = struct.pack("<L", symbol_va)
elif is_x64:
symbol_va = (int(k, 16) + 1) + 0xFFFFFFFF80000000
symbol_addr_raw = struct.pack("<Q", symbol_va)
#print ":: Looking up %s - %s" % (v, hex(symbol_va).strip("L"))
symbol = lookup(m, ksymtab_pa, symbol_addr_raw)
system_map[symbol] = v
for k, v in system_map.items():
print "%s %s %s" % (hex(k).strip("L")[2:], "?", v)
os.close(fd)
m.close()
main()