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

9 Dec 2020

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 -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

    