tools/efivar.py

   1 #!/usr/bin/env python3
   2 ## SPDX-License-Identifier: GPL-2.0-only
   3 #
   4 # EFI variable store utilities.
   5 #
   6 # (c) 2020 Paulo Alcantara <palcantara@suse.de>
   7 #
   8
   9 import os
  10 import struct
  11 import uuid
  12 import time
  13 import zlib
  14 import argparse
  15 from OpenSSL import crypto
  16
  17 # U-Boot variable store format (version 1)
  18 UBOOT_EFI_VAR_FILE_MAGIC = 0x0161566966456255
  19
  20 # UEFI variable attributes
  21 EFI_VARIABLE_NON_VOLATILE = 0x1
  22 EFI_VARIABLE_BOOTSERVICE_ACCESS = 0x2
  23 EFI_VARIABLE_RUNTIME_ACCESS = 0x4
  24 EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS = 0x10
  25 EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS = 0x20
  26 EFI_VARIABLE_READ_ONLY = 1 << 31
  27 NV_BS = EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS
  28 NV_BS_RT = NV_BS | EFI_VARIABLE_RUNTIME_ACCESS
  29 NV_BS_RT_AT = NV_BS_RT | EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
  30 DEFAULT_VAR_ATTRS = NV_BS_RT
  31
  32 # vendor GUIDs
  33 EFI_GLOBAL_VARIABLE_GUID = '8be4df61-93ca-11d2-aa0d-00e098032b8c'
  34 EFI_IMAGE_SECURITY_DATABASE_GUID = 'd719b2cb-3d3a-4596-a3bc-dad00e67656f'
  35 EFI_CERT_TYPE_PKCS7_GUID = '4aafd29d-68df-49ee-8aa9-347d375665a7'
  36 WIN_CERT_TYPE_EFI_GUID = 0x0ef1
  37 WIN_CERT_REVISION = 0x0200
  38
  39 var_attrs = {
  40         'NV': EFI_VARIABLE_NON_VOLATILE,
  41         'BS': EFI_VARIABLE_BOOTSERVICE_ACCESS,
  42         'RT': EFI_VARIABLE_RUNTIME_ACCESS,
  43         'AT': EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS,
  44         'RO': EFI_VARIABLE_READ_ONLY,
  45         'AW': EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS,
  46 }
  47
  48 var_guids = {
  49         'EFI_GLOBAL_VARIABLE_GUID': EFI_GLOBAL_VARIABLE_GUID,
  50         'EFI_IMAGE_SECURITY_DATABASE_GUID': EFI_IMAGE_SECURITY_DATABASE_GUID,
  51 }
  52
  53 class EfiStruct:
  54     # struct efi_var_file
  55     var_file_fmt = '<QQLL'
  56     var_file_size = struct.calcsize(var_file_fmt)
  57     # struct efi_var_entry
  58     var_entry_fmt = '<LLQ16s'
  59     var_entry_size = struct.calcsize(var_entry_fmt)
  60     # struct efi_time
  61     var_time_fmt = '<H6BLh2B'
  62     var_time_size = struct.calcsize(var_time_fmt)
  63     # WIN_CERTIFICATE
  64     var_win_cert_fmt = '<L2H'
  65     var_win_cert_size = struct.calcsize(var_win_cert_fmt)
  66     # WIN_CERTIFICATE_UEFI_GUID
  67     var_win_cert_uefi_guid_fmt = var_win_cert_fmt+'16s'
  68     var_win_cert_uefi_guid_size = struct.calcsize(var_win_cert_uefi_guid_fmt)
  69
  70 class EfiVariable:
  71     def __init__(self, size, attrs, time, guid, name, data):
  72         self.size = size
  73         self.attrs = attrs
  74         self.time = time
  75         self.guid = guid
  76         self.name = name
  77         self.data = data
  78
  79 def calc_crc32(buf):
  80     return zlib.crc32(buf) & 0xffffffff
  81
  82 class EfiVariableStore:
  83     def __init__(self, infile):
  84         self.infile = infile
  85         self.efi = EfiStruct()
  86         if os.path.exists(self.infile) and os.stat(self.infile).st_size > self.efi.var_file_size:
  87             with open(self.infile, 'rb') as f:
  88                 buf = f.read()
  89                 self._check_header(buf)
  90                 self.ents = buf[self.efi.var_file_size:]
  91         else:
  92             self.ents = bytearray()
  93
  94     def _check_header(self, buf):
  95         hdr = struct.unpack_from(self.efi.var_file_fmt, buf, 0)
  96         magic, crc32 = hdr[1], hdr[3]
  97
  98         if magic != UBOOT_EFI_VAR_FILE_MAGIC:
  99             print("err: invalid magic number: %s"%hex(magic))
 100             exit(1)
 101         if crc32 != calc_crc32(buf[self.efi.var_file_size:]):
 102             print("err: invalid crc32: %s"%hex(crc32))
 103             exit(1)
 104
 105     def _get_var_name(self, buf):
 106         name = ''
 107         for i in range(0, len(buf) - 1, 2):
 108             if not buf[i] and not buf[i+1]:
 109                 break
 110             name += chr(buf[i])
 111         return ''.join([chr(x) for x in name.encode('utf_16_le') if x]), i + 2
 112
 113     def _next_var(self, offs=0):
 114         size, attrs, time, guid = struct.unpack_from(self.efi.var_entry_fmt, self.ents, offs)
 115         data_fmt = str(size)+"s"
 116         offs += self.efi.var_entry_size
 117         name, namelen = self._get_var_name(self.ents[offs:])
 118         offs += namelen
 119         data = struct.unpack_from(data_fmt, self.ents, offs)[0]
 120         # offset to next 8-byte aligned variable entry
 121         offs = (offs + len(data) + 7) & ~7
 122         return EfiVariable(size, attrs, time, uuid.UUID(bytes_le=guid), name, data), offs
 123
 124     def __iter__(self):
 125         self.offs = 0
 126         return self
 127
 128     def __next__(self):
 129         if self.offs < len(self.ents):
 130             var, noffs = self._next_var(self.offs)
 131             self.offs = noffs
 132             return var
 133         else:
 134             raise StopIteration
 135
 136     def __len__(self):
 137         return len(self.ents)
 138
 139     def _set_var(self, guid, name_data, size, attrs, tsec):
 140         ent = struct.pack(self.efi.var_entry_fmt,
 141                           size,
 142                           attrs,
 143                           tsec,
 144                           uuid.UUID(guid).bytes_le)
 145         ent += name_data
 146         self.ents += ent
 147
 148     def del_var(self, guid, name, attrs):
 149         offs = 0
 150         while offs < len(self.ents):
 151             var, loffs = self._next_var(offs)
 152             if var.name == name and str(var.guid) == guid:
 153                 if var.attrs != attrs:
 154                     print("err: attributes don't match")
 155                     exit(1)
 156                 self.ents = self.ents[:offs] + self.ents[loffs:]
 157                 return
 158             offs = loffs
 159         print("err: variable not found")
 160         exit(1)
 161
 162     def set_var(self, guid, name, data, size, attrs):
 163         offs = 0
 164         while offs < len(self.ents):
 165             var, loffs = self._next_var(offs)
 166             if var.name == name and str(var.guid) == guid:
 167                 if var.attrs != attrs:
 168                     print("err: attributes don't match")
 169                     exit(1)
 170                 # make room for updating var
 171                 self.ents = self.ents[:offs] + self.ents[loffs:]
 172                 break
 173             offs = loffs
 174
 175         tsec = int(time.time()) if attrs & EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS else 0
 176         nd = name.encode('utf_16_le') + b"\x00\x00" + data
 177         # U-Boot variable format requires the name + data blob to be 8-byte aligned
 178         pad = ((len(nd) + 7) & ~7) - len(nd)
 179         nd += bytes([0] * pad)
 180
 181         return self._set_var(guid, nd, size, attrs, tsec)
 182
 183     def save(self):
 184         hdr = struct.pack(self.efi.var_file_fmt,
 185                           0,
 186                           UBOOT_EFI_VAR_FILE_MAGIC,
 187                           len(self.ents) + self.efi.var_file_size,
 188                           calc_crc32(self.ents))
 189
 190         with open(self.infile, 'wb') as f:
 191             f.write(hdr)
 192             f.write(self.ents)
 193
 194 def parse_attrs(attrs):
 195     v = DEFAULT_VAR_ATTRS
 196     if attrs:
 197         v = 0
 198         for i in attrs.split(','):
 199             v |= var_attrs[i.upper()]
 200     return v
 201
 202 def parse_data(val, vtype):
 203     if not val or not vtype:
 204         return None, 0
 205     fmt = { 'u8': '<B', 'u16': '<H', 'u32': '<L', 'u64': '<Q' }
 206     if vtype.lower() == 'file':
 207         with open(val, 'rb') as f:
 208             data = f.read()
 209             return data, len(data)
 210     if vtype.lower() == 'str':
 211         data = val.encode('utf-8')
 212         return data, len(data)
 213     if vtype.lower() == 'nil':
 214         return None, 0
 215     i = fmt[vtype.lower()]
 216     return struct.pack(i, int(val)), struct.calcsize(i)
 217
 218 def parse_args(args):
 219     name = args.name
 220     attrs = parse_attrs(args.attrs)
 221     guid = args.guid if args.guid else EFI_GLOBAL_VARIABLE_GUID
 222
 223     if name.lower() == 'db' or name.lower() == 'dbx':
 224         name = name.lower()
 225         guid = EFI_IMAGE_SECURITY_DATABASE_GUID
 226         attrs = NV_BS_RT_AT
 227     elif name.lower() == 'pk' or name.lower() == 'kek':
 228         name = name.upper()
 229         guid = EFI_GLOBAL_VARIABLE_GUID
 230         attrs = NV_BS_RT_AT
 231
 232     data, size = parse_data(args.data, args.type)
 233     return guid, name, attrs, data, size
 234
 235 def cmd_set(args):
 236     env = EfiVariableStore(args.infile)
 237     guid, name, attrs, data, size = parse_args(args)
 238     env.set_var(guid=guid, name=name, data=data, size=size, attrs=attrs)
 239     env.save()
 240
 241 def print_var(var):
 242     print(var.name+':')
 243     print("    "+str(var.guid)+' '+''.join([x for x in var_guids if str(var.guid) == var_guids[x]]))
 244     print("    "+'|'.join([x for x in var_attrs if var.attrs & var_attrs[x]])+", DataSize = %s"%hex(var.size))
 245     hexdump(var.data)
 246
 247 def cmd_print(args):
 248     env = EfiVariableStore(args.infile)
 249     if not args.name and not args.guid and not len(env):
 250         return
 251
 252     found = False
 253     for var in env:
 254         if not args.name:
 255             if args.guid and args.guid != str(var.guid):
 256                 continue
 257             print_var(var)
 258             found = True
 259         else:
 260             if args.name != var.name or (args.guid and args.guid != str(var.guid)):
 261                 continue
 262             print_var(var)
 263             found = True
 264
 265     if not found:
 266         print("err: variable not found")
 267         exit(1)
 268
 269 def cmd_del(args):
 270     env = EfiVariableStore(args.infile)
 271     attrs = parse_attrs(args.attrs)
 272     guid = args.guid if args.guid else EFI_GLOBAL_VARIABLE_GUID
 273     env.del_var(guid, args.name, attrs)
 274     env.save()
 275
 276 def pkcs7_sign(cert, key, buf):
 277     with open(cert, 'r') as f:
 278         crt = crypto.load_certificate(crypto.FILETYPE_PEM, f.read())
 279     with open(key, 'r') as f:
 280         pkey = crypto.load_privatekey(crypto.FILETYPE_PEM, f.read())
 281
 282     PKCS7_BINARY = 0x80
 283     PKCS7_DETACHED = 0x40
 284     PKCS7_NOATTR = 0x100
 285
 286     bio_in = crypto._new_mem_buf(buf)
 287     p7 = crypto._lib.PKCS7_sign(crt._x509, pkey._pkey, crypto._ffi.NULL, bio_in,
 288                                 PKCS7_BINARY|PKCS7_DETACHED|PKCS7_NOATTR)
 289     bio_out = crypto._new_mem_buf()
 290     crypto._lib.i2d_PKCS7_bio(bio_out, p7)
 291     return crypto._bio_to_string(bio_out)
 292
 293 # UEFI 2.8 Errata B "8.2.2 Using the EFI_VARIABLE_AUTHENTICATION_2 descriptor"
 294 def cmd_sign(args):
 295     guid, name, attrs, data, _ = parse_args(args)
 296     attrs |= EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
 297     efi = EfiStruct()
 298
 299     tm = time.localtime()
 300     etime = struct.pack(efi.var_time_fmt,
 301                         tm.tm_year, tm.tm_mon, tm.tm_mday,
 302                         tm.tm_hour, tm.tm_min, tm.tm_sec,
 303                         0, 0, 0, 0, 0)
 304
 305     buf = name.encode('utf_16_le') + uuid.UUID(guid).bytes_le + attrs.to_bytes(4, byteorder='little') + etime
 306     if data:
 307         buf += data
 308     sig = pkcs7_sign(args.cert, args.key, buf)
 309
 310     desc = struct.pack(efi.var_win_cert_uefi_guid_fmt,
 311                        efi.var_win_cert_uefi_guid_size + len(sig),
 312                        WIN_CERT_REVISION,
 313                        WIN_CERT_TYPE_EFI_GUID,
 314                        uuid.UUID(EFI_CERT_TYPE_PKCS7_GUID).bytes_le)
 315
 316     with open(args.outfile, 'wb') as f:
 317         if data:
 318             f.write(etime + desc + sig + data)
 319         else:
 320             f.write(etime + desc + sig)
 321
 322 def main():
 323     ap = argparse.ArgumentParser(description='EFI variable store utilities')
 324     subp = ap.add_subparsers(help="sub-command help")
 325
 326     printp = subp.add_parser('print', help='get/list EFI variables')
 327     printp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
 328     printp.add_argument('--name', '-n', help='variable name')
 329     printp.add_argument('--guid', '-g', help='vendor GUID')
 330     printp.set_defaults(func=cmd_print)
 331
 332     setp = subp.add_parser('set', help='set EFI variable')
 333     setp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
 334     setp.add_argument('--name', '-n', required=True, help='variable name')
 335     setp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
 336     setp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
 337     setp.add_argument('--type', '-t', help='variable type (values: file|u8|u16|u32|u64|str)')
 338     setp.add_argument('--data', '-d', help='data or filename')
 339     setp.set_defaults(func=cmd_set)
 340
 341     delp = subp.add_parser('del', help='delete EFI variable')
 342     delp.add_argument('--infile', '-i', required=True, help='file to save the EFI variables')
 343     delp.add_argument('--name', '-n', required=True, help='variable name')
 344     delp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
 345     delp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
 346     delp.set_defaults(func=cmd_del)
 347
 348     signp = subp.add_parser('sign', help='sign time-based EFI payload')
 349     signp.add_argument('--cert', '-c', required=True, help='x509 certificate filename in PEM format')
 350     signp.add_argument('--key', '-k', required=True, help='signing certificate filename in PEM format')
 351     signp.add_argument('--name', '-n', required=True, help='variable name')
 352     signp.add_argument('--attrs', '-a', help='variable attributes (values: nv,bs,rt,at,ro,aw)')
 353     signp.add_argument('--guid', '-g', help="vendor GUID (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
 354     signp.add_argument('--type', '-t', required=True, help='variable type (values: file|u8|u16|u32|u64|str|nil)')
 355     signp.add_argument('--data', '-d', help='data or filename')
 356     signp.add_argument('--outfile', '-o', required=True, help='output filename of signed EFI payload')
 357     signp.set_defaults(func=cmd_sign)
 358
 359     args = ap.parse_args()
 360     if hasattr(args, "func"):
 361         args.func(args)
 362     else:
 363         ap.print_help()
 364
 365 def group(a, *ns):
 366     for n in ns:
 367         a = [a[i:i+n] for i in range(0, len(a), n)]
 368     return a
 369
 370 def join(a, *cs):
 371     return [cs[0].join(join(t, *cs[1:])) for t in a] if cs else a
 372
 373 def hexdump(data):
 374     toHex = lambda c: '{:02X}'.format(c)
 375     toChr = lambda c: chr(c) if 32 <= c < 127 else '.'
 376     make = lambda f, *cs: join(group(list(map(f, data)), 8, 2), *cs)
 377     hs = make(toHex, '  ', ' ')
 378     cs = make(toChr, ' ', '')
 379     for i, (h, c) in enumerate(zip(hs, cs)):
 380         print ('    {:010X}: {:48}  {:16}'.format(i * 16, h, c))
 381
 382 if __name__ == '__main__':
 383     main()