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

[Paulo Alcantara]

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

An example of generating secure boot variables

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

Signed-off-by: Paulo Alcantara (SUSE) <pc at cjr.nz>
---
 tools/efivar.py | 141 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100755 tools/efivar.py

diff --git a/tools/efivar.py b/tools/efivar.py
new file mode 100755
index 000000000000..31e5508f08fd
--- /dev/null
+++ b/tools/efivar.py
@@ -0,0 +1,141 @@
+#!/usr/bin/env python3
+## SPDX-License-Identifier: GPL-2.0-only
+#
+# Generate UEFI variables for U-Boot.
+#
+# (c) 2020 Paulo Alcantara <palcantara at suse.de>
+#
+
+import os
+import struct
+import uuid
+import time
+import zlib
+import argparse
+import subprocess as sp
+
+# 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_TIME_BASED_AUTHENTICATED_WRITE_ACCESS = 0x20
+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
+
+# UEFI variable GUIDs
+EFI_GLOBAL_VARIABLE_GUID = '{8be4df61-93ca-11d2-aa0d-00e098032b8c}'
+EFI_IMAGE_SECURITY_DATABASE_GUID = '{d719b2cb-3d3a-4596-a3bc-dad00e67656f}'
+
+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)
+
+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:
+                # skip header since it will be recreated by save()
+                self.buf = f.read()[self.efi.var_file_size:]
+        else:
+            self.buf = bytearray()
+
+    def _set_var(self, guid, name_data, size, attr, tsec):
+        ent = struct.pack(self.efi.var_entry_fmt,
+                          size,
+                          attr,
+                          tsec,
+                          uuid.UUID(guid).bytes_le)
+        ent += name_data
+        self.buf += ent
+
+    def set_var(self, guid, name, data, size, attr):
+        tsec = int(time.time()) if attr & 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, attr, tsec)
+
+    def save(self):
+        hdr = struct.pack(self.efi.var_file_fmt,
+                          0,
+                          UBOOT_EFI_VAR_FILE_MAGIC,
+                          len(self.buf) + self.efi.var_file_size,
+                          zlib.crc32(self.buf) & 0xffffffff)
+
+        with open(self.infile, 'wb') as f:
+            f.write(hdr)
+            f.write(self.buf)
+
+def parse_attrs(attr):
+    attrs = {
+            'nv': EFI_VARIABLE_NON_VOLATILE,
+            'bs': EFI_VARIABLE_BOOTSERVICE_ACCESS,
+            'rt': EFI_VARIABLE_RUNTIME_ACCESS,
+            'at': EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS,
+    }
+    v = 0
+    for i in attr.split(','):
+       v |= attrs[i.lower()]
+    return v
+
+def parse_data(val, vtype):
+    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') + b'\x00'
+        return data, len(data)
+    i = fmt[vtype.lower()]
+    return struct.pack(i, int(val)), struct.calcsize(i)
+
+def cmd_add(args):
+    env = EfiVariableStore(args.infile)
+    data, size = parse_data(args.data, args.type)
+
+    if args.name.lower() == 'pk':
+        env.set_var(guid=EFI_GLOBAL_VARIABLE_GUID, name='PK', data=data, size=size, attr=NV_BS_RT_AT)
+    elif args.name.lower() == 'kek':
+        env.set_var(guid=EFI_GLOBAL_VARIABLE_GUID, name='KEK', data=data, size=size, attr=NV_BS_RT_AT)
+    elif args.name.lower() == 'db':
+        env.set_var(guid=EFI_IMAGE_SECURITY_DATABASE_GUID, name='db', data=data, size=size, attr=NV_BS_RT_AT)
+    elif args.name.lower() == 'dbx':
+        env.set_var(guid=EFI_IMAGE_SECURITY_DATABASE_GUID, name='dbx', data=data, size=size, attr=NV_BS_RT_AT)
+    else:
+        guid = args.guid if args.guid else EFI_GLOBAL_VARIABLE_GUID
+        attr = parse_attrs(args.attr) if args.attr else NV_BS
+        env.set_var(guid=guid, name=args.name, data=data, size=size, attr=attr)
+
+    env.save()
+
+def main():
+    ap = argparse.ArgumentParser(description='Generate U-Boot variable store')
+    ap.add_argument('--infile', '-i', required=True, help='file to save the UEFI variables')
+    subp = ap.add_subparsers(help="sub-command help")
+
+    addp = subp.add_parser('add', help='add UEFI variable')
+    addp.add_argument('--name', '-n', required=True, help='variable name')
+    addp.add_argument('--attr', '-a', help='variable attributes (default: nv,bs)')
+    addp.add_argument('--guid', '-g', help="variable guid (default: %s)"%EFI_GLOBAL_VARIABLE_GUID)
+    addp.add_argument('--type', '-t', required=True, help='variable type (values: file|u8|u16|u32|u64|str)')
+    addp.add_argument('--data', '-d', required=True, help='variable data')
+    addp.set_defaults(func=cmd_add)
+
+    args = ap.parse_args()
+    args.func(args)
+
+if __name__ == '__main__':
+    main()
-- 
2.29.2