Re: [PATCH v4] tools: add a simple script to generate EFI variables

On 12/9/20 12:10 AM, Paulo Alcantara wrote:

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

A few examples:

• Generating secure boot keys

  $ openssl x509 -in foo.crt -outform DER -out foo.der $ efisiglist -a -c foo.der -o foo.esl $ ./efivar.py -i ubootefi.var set -n db -d foo.esl -t file $ ./efivar.py -i ubootefi.var set -n kek -d foo.esl -t file

efivar.py requires that 'set' is the first parameter. I will fix the commit message.

Could you, please, provide a man-page for the tool as restructured text in doc/usage/. Please, check that it is correct with 'make htmldocs'.

Best regards

Heinrich

 $ ./efivar.py -i ubootefi.var set -n pk -d foo.esl -t file

• Printing out variables

  $ ./efivar.py -i ubootefi.var set -n var1 -d foo -t str $ ./efivar.py -i ubootefi.var set -n var2 -d bar -t str $ ./efivar.py -i ubootefi.var print 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

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

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

v4: add 'sign' command for authenticated EFI payloads

tools/efivar.py | 380 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 380 insertions(+) create mode 100755 tools/efivar.py

diff --git a/tools/efivar.py b/tools/efivar.py new file mode 100755 index 000000000000..ebfcab2f0a2c --- /dev/null +++ b/tools/efivar.py @@ -0,0 +1,380 @@ +#!/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()

-- 2.29.2