tpm_handler.py revision 9999730bc117c6a6363b616d3da5dbf0eb6b4d50 
1# Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5"""A module containing TPM handler class used by SAFT."""
6
7FW_NV_ADDRESS = 0x1007
8KERNEL_NV_ADDRESS = 0x1008
9
10class TpmError(Exception):
11    pass
12
13class TpmNvRam(object):
14    """An object representing TPM NvRam.
15
16    Attributes:
17    addr: a number, NvRAm address in TPM.
18    size: a number, count of bites in this NvRam section.
19    os_if: an instance of the OS interface (chromeos_interface or a mock
20        object).
21    version_offset: - a number, offset into the NvRam contents where the the
22        versions are stored. The total version field size is 4 bytes, the
23        first two bytes are the body version, the second two bytes are the key
24        version. Numbers are stored in little endian format.
25    pattern: optional, a tuple of two elements, the first element is the
26       offset of the pattern expected to be present in the NvRam, and the
27       second element is an array of bytes the pattern must match.
28    contents: an array of bytes, the contents of the NvRam.
29    """
30
31    def __init__(self, addr, size, version_offset, data_pattern=None):
32        self.addr = addr
33        self.size = size
34        self.os_if = None
35        self.version_offset = version_offset
36        self.pattern = data_pattern
37        self.contents = []
38
39    def init(self, os_if):
40        self.os_if = os_if
41        cmd = 'tpmc read 0x%x 0x%x' % (self.addr, self.size)
42        nvram_data = self.os_if.run_shell_command_get_output(cmd)[0].split()
43        self.contents = [int(x, 16) for x in nvram_data]
44        if self.pattern:
45            pattern_offset = self.pattern[0]
46            pattern_data = self.pattern[1]
47            contents_pattern = self.contents[pattern_offset:pattern_offset +
48                                             len(pattern_data)]
49            if contents_pattern != pattern_data:
50                raise TpmError('Nvram pattern does not match')
51
52    def get_body_version(self):
53        return self.contents[
54            self.version_offset + 1] * 256 + self.contents[self.version_offset]
55
56    def get_key_version(self):
57        return self.contents[
58            self.version_offset + 3] * 256 + self.contents[
59            self.version_offset + 2]
60
61class TpmHandler(object):
62    """An object to control TPM device's NVRAM.
63
64    Attributes:
65      cros_if: an instance of the OS interface (chromeos_interface or a mock
66          object).
67      nvrams: A dictionary where the keys are the nvram names, and the values
68          are instances of TpmNvRam objects, providing access to the
69          appropriate TPM NvRam sections.
70    """
71
72    def __init__(self):
73        self.cros_if = None
74        self.nvrams = {
75            'kernel': TpmNvRam(KERNEL_NV_ADDRESS, 13, 5, (
76                    1, [0x4c, 0x57, 0x52, 0x47])),
77            'bios': TpmNvRam(FW_NV_ADDRESS, 10, 2)
78            }
79
80    def init(self, cros_if):
81        self.cros_if = cros_if
82        status = self.cros_if.run_shell_command_get_output(
83            'initctl status tcsd')[0]
84        if status.startswith('tcsd start/running'):
85            self.cros_if.run_shell_command('stop tcsd')
86
87        for nvram in self.nvrams.itervalues():
88            nvram.init(self.cros_if)
89
90    def get_fw_version(self):
91        return self.nvrams['bios'].get_body_version()
92
93    def get_fw_body_version(self):
94        return self.nvrams['bios'].get_key_version()
95
96    def get_kernel_version(self):
97        return self.nvrams['kernel'].get_body_version()
98