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#!/usr/bin/python
#
# based on pyuefivars which is:
# Copyright Amazon.com, Inc.
# SPDX-License-Identifier: MIT
#
""" aws varstore parser """
import sys
import zlib
import base64
import struct
import logging
import importlib_resources
from virt.firmware.efi import guids
from virt.firmware.efi import ucs16
from virt.firmware.efi import efivar
# pylint: disable=ungrouped-imports
try:
from crc32c import crc32c
except ModuleNotFoundError:
from virt.firmware.misc import crc32c
zdict_v0_file = importlib_resources.files('virt.firmware') / 'aws/dict.v0'
zdict_v0_blob = None
# pylint: disable=global-statement
def zdict_v0():
global zdict_v0_blob
if zdict_v0_blob is None:
with open(zdict_v0_file, "rb") as f:
zdict_v0_blob = f.read()
return zdict_v0_blob
class AwsVarStore:
""" class for aws efi varstore """
MAGIC = 0x494645554e5a4d41
def __init__(self, filename = None):
self.filename = filename
self.filedata = b''
self.vardata = b''
self.varpos = 0
if self.filename:
self.readfile()
self.parse()
@staticmethod
def probe(filename):
with open(filename, "rb") as f:
try:
data = base64.b64decode(f.read())
except base64.binascii.Error:
return False
(magic, crc32, version) = struct.unpack_from("=QLL", data, 0)
if magic != AwsVarStore.MAGIC:
return False
return True
def readfile(self):
logging.info('reading aws varstore from %s', self.filename)
with open(self.filename, "rb") as f:
self.filedata = base64.b64decode(f.read())
def parse(self):
(magic, crc32, version) = struct.unpack_from("=QLL", self.filedata, 0)
logging.debug('magic=0x%x crc32=0x%x version=%d',
magic, crc32, version)
if magic != self.MAGIC:
logging.error('%s: aws magic mismatch', self.filename)
sys.exit(1)
if crc32c(self.filedata[ 12 : ]) != crc32:
logging.error('%s: crc32c mismatch', self.filename)
sys.exit(1)
if version != 0:
logging.error('%s: unknnown version', self.filename)
sys.exit(1)
decompressor = zlib.decompressobj(0, zdict = zdict_v0())
self.vardata = decompressor.decompress(self.filedata[ 16 : ])
def get_int(self, bits):
s = int(bits / 8)
d = self.vardata [ self.varpos : self.varpos + s ]
i = int.from_bytes(d, byteorder='little', signed=False)
self.varpos += s
return i
def get_blob(self):
size = self.get_int(64)
blob = self.vardata [ self.varpos : self.varpos + size ]
self.varpos += size
return blob
def get_guid(self):
guid = guids.parse_bin(self.vardata, self.varpos)
self.varpos += 16
return guid
def get_time(self):
blob = self.vardata [ self.varpos : self.varpos + 16 ]
self.varpos += 16
return blob
# pylint: disable=W0511
def get_varlist(self):
self.varpos = 0
count = self.get_int(64)
varlist = efivar.EfiVarList()
for index in range(count):
name = self.get_blob()
data = self.get_blob()
guid = self.get_guid()
attr = self.get_int(32)
var = efivar.EfiVar(ucs16.from_string(name.decode('utf-8')),
guid = guid, attr = attr, data = data)
if attr & efivar.EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS:
timestamp = self.get_time()
var.parse_time(timestamp, 0)
digest = self.get_blob() # FIXME
varlist[str(var.name)] = var
return varlist
# pylint: disable=W0511
@staticmethod
def bytes_var(var):
name = str(var.name).encode('utf-8')
blob = struct.pack("=Q", len(name))
blob += name
blob += struct.pack("=Q", len(var.data))
blob += var.data
blob += var.guid.bytes_le
blob += struct.pack("=L", var.attr)
if var.attr & efivar.EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS:
blob += var.bytes_time()
blob += struct.pack("=Q", 0) # FIXME: empty digest
return blob
@staticmethod
def bytes_varlist(varlist):
blob = struct.pack("=Q", len(varlist))
for (key, item) in sorted(varlist.items()):
blob += AwsVarStore.bytes_var(item)
return blob
@staticmethod
def base64_varstore(varlist):
encoder = zlib.compressobj(9, zdict = zdict_v0())
zblob = struct.pack("=L", 0) # version
zblob += encoder.compress(AwsVarStore.bytes_varlist(varlist))
zblob += encoder.flush()
hdr = struct.pack("=QL", AwsVarStore.MAGIC, crc32c(zblob))
return base64.b64encode(hdr + zblob)
@staticmethod
def write_varstore(filename, varlist):
logging.info('writing aws varstore to %s', filename)
blob = AwsVarStore.base64_varstore(varlist)
with open(filename, "wb") as f:
f.write(blob)
if __name__ == "__main__":
logging.basicConfig(format = '%(levelname)s: %(message)s',
level = logging.DEBUG)
testfile = "tests/data/secboot.aws"
if AwsVarStore.probe(testfile):
awsstore = AwsVarStore(testfile)
vl = awsstore.get_varlist()
vl.print_normal()
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