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tools: add a simple script to generate EFI variables

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This script generates EFI variables for U-Boot variable store format.

A few examples:

  - Generating secure boot keys

    $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_PK/ \
            -keyout PK.key -out PK.crt -nodes -days 365
    $ efisiglist -a -c PK.crt -o foo.esl
    $ tools/efivar.py set -i ubootefi.var -n db -d foo.esl -t file
    $ tools/efivar.py set -i ubootefi.var -n kek -d foo.esl -t file
    $ tools/efivar.py set -i ubootefi.var -n pk -d foo.esl -t file

  - Printing out variables

    $ tools/efivar.py set -i ubootefi.var -n var1 -d foo -t str
    $ tools/efivar.py set -i ubootefi.var -n var2 -d bar -t str
    $ tools/efivar.py print -i ubootefi.var
    var1:
        8be4df61-93ca-11d2-aa0d-00e098032b8c EFI_GLOBAL_VARIABLE_GUID
        NV|BS|RT, DataSize = 0x3
        0000000000: 66 6F 6F                                          foo
    var2:
        8be4df61-93ca-11d2-aa0d-00e098032b8c EFI_GLOBAL_VARIABLE_GUID
        NV|BS|RT, DataSize = 0x3
        0000000000: 62 61 72                                          bar

    - Removing variables

      $ tools/efivar.py del -i ubootefi.var -n var1
      $ tools/efivar.py set -i ubootefi.var -n var1 -a nv,bs -d foo -t str
      $ tools/efivar.py print -i ubootefi.var -n var1
      var1:
          8be4df61-93ca-11d2-aa0d-00e098032b8c EFI_GLOBAL_VARIABLE_GUID
          NV|BS, DataSize = 0x3
          0000000000: 66 6F 6F                                        foo
      $ tools/efivar.py del -i ubootefi.var -n var1
      err: attributes don't match
      $ tools/efivar.py del -i ubootefi.var -n var1 -a nv,bs
      $ tools/efivar.py print -i ubootefi.var -n var1
      err: variable not found

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>

Correct examples in commit message.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
This commit is contained in:
Paulo Alcantara 2020-12-08 20:10:48 -03:00 committed by Heinrich Schuchardt
parent 265ce19485
commit 73253d7765
1 changed files with 380 additions and 0 deletions
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#!/usr/bin/env python3
## SPDX-License-Identifier: GPL-2.0-only
#
# EFI variable store utilities.
#
# (c) 2020 Paulo Alcantara <palcantara@suse.de>
#
import os
import struct
import uuid
import time
import zlib
import argparse
from OpenSSL import crypto
# U-Boot variable store format (version 1)
UBOOT_EFI_VAR_FILE_MAGIC = 0x0161566966456255
# UEFI variable attributes
EFI_VARIABLE_NON_VOLATILE = 0x1
EFI_VARIABLE_BOOTSERVICE_ACCESS = 0x2
EFI_VARIABLE_RUNTIME_ACCESS = 0x4
EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS = 0x10
EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS = 0x20
EFI_VARIABLE_READ_ONLY = 1 << 31
NV_BS = EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS
NV_BS_RT = NV_BS | EFI_VARIABLE_RUNTIME_ACCESS
NV_BS_RT_AT = NV_BS_RT | EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
DEFAULT_VAR_ATTRS = NV_BS_RT
# vendor GUIDs
EFI_GLOBAL_VARIABLE_GUID = '8be4df61-93ca-11d2-aa0d-00e098032b8c'
EFI_IMAGE_SECURITY_DATABASE_GUID = 'd719b2cb-3d3a-4596-a3bc-dad00e67656f'
EFI_CERT_TYPE_PKCS7_GUID = '4aafd29d-68df-49ee-8aa9-347d375665a7'
WIN_CERT_TYPE_EFI_GUID = 0x0ef1
WIN_CERT_REVISION = 0x0200
var_attrs = {
'NV': EFI_VARIABLE_NON_VOLATILE,
'BS': EFI_VARIABLE_BOOTSERVICE_ACCESS,
'RT': EFI_VARIABLE_RUNTIME_ACCESS,
'AT': EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS,
'RO': EFI_VARIABLE_READ_ONLY,
'AW': EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS,
}
var_guids = {
'EFI_GLOBAL_VARIABLE_GUID': EFI_GLOBAL_VARIABLE_GUID,
'EFI_IMAGE_SECURITY_DATABASE_GUID': EFI_IMAGE_SECURITY_DATABASE_GUID,
}
class EfiStruct:
# struct efi_var_file
var_file_fmt = '<QQLL'
var_file_size = struct.calcsize(var_file_fmt)
# struct efi_var_entry
var_entry_fmt = '<LLQ16s'
var_entry_size = struct.calcsize(var_entry_fmt)
# struct efi_time
var_time_fmt = '<H6BLh2B'
var_time_size = struct.calcsize(var_time_fmt)
# WIN_CERTIFICATE
var_win_cert_fmt = '<L2H'
var_win_cert_size = struct.calcsize(var_win_cert_fmt)
# WIN_CERTIFICATE_UEFI_GUID
var_win_cert_uefi_guid_fmt = var_win_cert_fmt+'16s'
var_win_cert_uefi_guid_size = struct.calcsize(var_win_cert_uefi_guid_fmt)
class EfiVariable:
def __init__(self, size, attrs, time, guid, name, data):
self.size = size
self.attrs = attrs
self.time = time
self.guid = guid
self.name = name
self.data = data
def calc_crc32(buf):
return zlib.crc32(buf) & 0xffffffff
class EfiVariableStore:
def __init__(self, infile):
self.infile = infile
self.efi = EfiStruct()
if os.path.exists(self.infile) and os.stat(self.infile).st_size > self.efi.var_file_size:
with open(self.infile, 'rb') as f:
buf = f.read()
self._check_header(buf)
self.ents = buf[self.efi.var_file_size:]
else:
self.ents = bytearray()
def _check_header(self, buf):
hdr = struct.unpack_from(self.efi.var_file_fmt, buf, 0)
magic, crc32 = hdr[1], hdr[3]
if magic != UBOOT_EFI_VAR_FILE_MAGIC:
print("err: invalid magic number: %s"%hex(magic))
exit(1)
if crc32 != calc_crc32(buf[self.efi.var_file_size:]):
print("err: invalid crc32: %s"%hex(crc32))
exit(1)
def _get_var_name(self, buf):
name = ''
for i in range(0, len(buf) - 1, 2):
if not buf[i] and not buf[i+1]:
break
name += chr(buf[i])
return ''.join([chr(x) for x in name.encode('utf_16_le') if x]), i + 2
def _next_var(self, offs=0):
size, attrs, time, guid = struct.unpack_from(self.efi.var_entry_fmt, self.ents, offs)
data_fmt = str(size)+"s"
offs += self.efi.var_entry_size
name, namelen = self._get_var_name(self.ents[offs:])
offs += namelen
data = struct.unpack_from(data_fmt, self.ents, offs)[0]
# offset to next 8-byte aligned variable entry
offs = (offs + len(data) + 7) & ~7
return EfiVariable(size, attrs, time, uuid.UUID(bytes_le=guid), name, data), offs
def __iter__(self):
self.offs = 0
return self
def __next__(self):
if self.offs < len(self.ents):
var, noffs = self._next_var(self.offs)
self.offs = noffs
return var
else:
raise StopIteration
def __len__(self):
return len(self.ents)
def _set_var(self, guid, name_data, size, attrs, tsec):
ent = struct.pack(self.efi.var_entry_fmt,
size,
attrs,
tsec,
uuid.UUID(guid).bytes_le)
ent += name_data
self.ents += ent
def del_var(self, guid, name, attrs):
offs = 0
while offs < len(self.ents):
var, loffs = self._next_var(offs)
if var.name == name and str(var.guid):
if var.attrs != attrs:
print("err: attributes don't match")
exit(1)
self.ents = self.ents[:offs] + self.ents[loffs:]
return
offs = loffs
print("err: variable not found")
exit(1)
def set_var(self, guid, name, data, size, attrs):
offs = 0
while offs < len(self.ents):
var, loffs = self._next_var(offs)
if var.name == name and str(var.guid) == guid:
if var.attrs != attrs:
print("err: attributes don't match")
exit(1)
# make room for updating var
self.ents = self.ents[:offs] + self.ents[loffs:]
break
offs = loffs
tsec = int(time.time()) if attrs & EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS else 0
nd = name.encode('utf_16_le') + b"\x00\x00" + data
# U-Boot variable format requires the name + data blob to be 8-byte aligned
pad = ((len(nd) + 7) & ~7) - len(nd)
nd += bytes([0] * pad)
return self._set_var(guid, nd, size, attrs, tsec)
def save(self):
hdr = struct.pack(self.efi.var_file_fmt,
0,
UBOOT_EFI_VAR_FILE_MAGIC,
len(self.ents) + self.efi.var_file_size,
calc_crc32(self.ents))
with open(self.infile, 'wb') as f:
f.write(hdr)
f.write(self.ents)
def parse_attrs(attrs):
v = DEFAULT_VAR_ATTRS
if attrs:
v = 0
for i in attrs.split(','):
v |= var_attrs[i.upper()]
return v
def parse_data(val, vtype):
if not val or not vtype:
return None, 0
fmt = { 'u8': '<B', 'u16': '<H', 'u32': '<L', 'u64': '<Q' }
if vtype.lower() == 'file':
with open(val, 'rb') as f:
data = f.read()
return data, len(data)
if vtype.lower() == 'str':
data = val.encode('utf-8')
return data, len(data)
if vtype.lower() == 'nil':
return None, 0
i = fmt[vtype.lower()]
return struct.pack(i, int(val)), struct.calcsize(i)
def parse_args(args):
name = args.name
attrs = parse_attrs(args.attrs)
guid = args.guid if args.guid else EFI_GLOBAL_VARIABLE_GUID
if name.lower() == 'db' or name.lower() == 'dbx':
name = name.lower()
guid = EFI_IMAGE_SECURITY_DATABASE_GUID
attrs = NV_BS_RT_AT
elif name.lower() == 'pk' or name.lower() == 'kek':
name = name.upper()
guid = EFI_GLOBAL_VARIABLE_GUID
attrs = NV_BS_RT_AT
data, size = parse_data(args.data, args.type)
return guid, name, attrs, data, size
def cmd_set(args):
env = EfiVariableStore(args.infile)
guid, name, attrs, data, size = parse_args(args)
env.set_var(guid=guid, name=name, data=data, size=size, attrs=attrs)
env.save()
def print_var(var):
print(var.name+':')
print(" "+str(var.guid)+' '+''.join([x for x in var_guids if str(var.guid) == var_guids[x]]))
print(" "+'|'.join([x for x in var_attrs if var.attrs & var_attrs[x]])+", DataSize = %s"%hex(var.size))
hexdump(var.data)
def cmd_print(args):
env = EfiVariableStore(args.infile)
if not args.name and not args.guid and not len(env):
return
found = False
for var in env:
if not args.name:
if args.guid and args.guid != str(var.guid):
continue
print_var(var)
found = True
else:
if args.name != var.name or (args.guid and args.guid != str(var.guid)):
continue
print_var(var)
found = True
if not found:
print("err: variable not found")
exit(1)
def cmd_del(args):
env = EfiVariableStore(args.infile)
attrs = parse_attrs(args.attrs)
guid = args.guid if args.guid else EFI_GLOBAL_VARIABLE_GUID
env.del_var(guid, args.name, attrs)
env.save()
def pkcs7_sign(cert, key, buf):
with open(cert, 'r') as f:
crt = crypto.load_certificate(crypto.FILETYPE_PEM, f.read())
with open(key, 'r') as f:
pkey = crypto.load_privatekey(crypto.FILETYPE_PEM, f.read())
PKCS7_BINARY = 0x80
PKCS7_DETACHED = 0x40
PKCS7_NOATTR = 0x100
bio_in = crypto._new_mem_buf(buf)
p7 = crypto._lib.PKCS7_sign(crt._x509, pkey._pkey, crypto._ffi.NULL, bio_in,
PKCS7_BINARY|PKCS7_DETACHED|PKCS7_NOATTR)
bio_out = crypto._new_mem_buf()
crypto._lib.i2d_PKCS7_bio(bio_out, p7)
return crypto._bio_to_string(bio_out)
# UEFI 2.8 Errata B "8.2.2 Using the EFI_VARIABLE_AUTHENTICATION_2 descriptor"
def cmd_sign(args):
guid, name, attrs, data, size = parse_args(args)
attrs |= EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
efi = EfiStruct()
tm = time.localtime()
etime = struct.pack(efi.var_time_fmt,
tm.tm_year, tm.tm_mon, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec,
0, 0, 0, 0, 0)
buf = name.encode('utf_16_le') + uuid.UUID(guid).bytes_le + attrs.to_bytes(4, byteorder='little') + etime
if data:
buf += data
sig = pkcs7_sign(args.cert, args.key, buf)
desc = struct.pack(efi.var_win_cert_uefi_guid_fmt,
efi.var_win_cert_uefi_guid_size + len(sig),
WIN_CERT_REVISION,
WIN_CERT_TYPE_EFI_GUID,
uuid.UUID(EFI_CERT_TYPE_PKCS7_GUID).bytes_le)
with open(args.outfile, 'wb') as f:
if data:
f.write(etime + desc + sig + data)
else:
f.write(etime + desc + sig)
def main():
ap = argparse.ArgumentParser(description='EFI variable store utilities')
subp = ap.add_subparsers(help="sub-command help")
printp = subp.add_parser('print', help='get/list EFI variables')
printp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
printp.add_argument('--name', '-n', help='variable name')
printp.add_argument('--guid', '-g', help='vendor GUID')
printp.set_defaults(func=cmd_print)
setp = subp.add_parser('set', help='set EFI variable')
setp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
setp.add_argument('--name', '-n', required=True, help='variable name')
setp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
setp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
setp.add_argument('--type', '-t', help='variable type (values: file|u8|u16|u32|u64|str)')
setp.add_argument('--data', '-d', help='data or filename')
setp.set_defaults(func=cmd_set)
delp = subp.add_parser('del', help='delete EFI variable')
delp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
delp.add_argument('--name', '-n', required=True, help='variable name')
delp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
delp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
delp.set_defaults(func=cmd_del)
signp = subp.add_parser('sign', help='sign time-based EFI payload')
signp.add_argument('--cert', '-c', required=True, help='x509 certificate filename in PEM format')
signp.add_argument('--key', '-k', required=True, help='signing certificate filename in PEM format')
signp.add_argument('--name', '-n', required=True, help='variable name')
signp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
signp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
signp.add_argument('--type', '-t', required=True, help='variable type (values: file|u8|u16|u32|u64|str|nil)')
signp.add_argument('--data', '-d', help='data or filename')
signp.add_argument('--outfile', '-o', required=True, help='output filename of signed EFI payload')
signp.set_defaults(func=cmd_sign)
args = ap.parse_args()
args.func(args)
def group(a, *ns):
for n in ns:
a = [a[i:i+n] for i in range(0, len(a), n)]
return a
def join(a, *cs):
return [cs[0].join(join(t, *cs[1:])) for t in a] if cs else a
def hexdump(data):
toHex = lambda c: '{:02X}'.format(c)
toChr = lambda c: chr(c) if 32 <= c < 127 else '.'
make = lambda f, *cs: join(group(list(map(f, data)), 8, 2), *cs)
hs = make(toHex, ' ', ' ')
cs = make(toChr, ' ', '')
for i, (h, c) in enumerate(zip(hs, cs)):
print (' {:010X}: {:48} {:16}'.format(i * 16, h, c))
if __name__ == '__main__':
main()