Add support for tapping into TPM communication

[hslatman]

This PR adds support for tapping into all communication to and from the TPM. It's currently only supported on Linux.

A couple concrete implementations of taps are provided too, incl. one that writes binary data by simply writing all reads and writes to a single io.Writer, and one that writes in pcapng format. The binary tap is compatible with https://github.com/joholl/tpmstream, and the output of the pcapng tap can be inspected using Wireshark (or compatible tooling).

Example output:

$ tpmstream convert out.bin
Command                                   .
TPMI_ST_COMMAND_TAG                       |   .tag                                       8001                 TPMI_ST_COMMAND_TAG.NO_SESSIONS
UINT32                                    |   .commandSize                               00000016             22
TPM_CC                                    |   .commandCode                               0000017a             TPM_CC.GetCapability
TPMS_COMMAND_HANDLES_GET_CAPABILITY       |   .handles
TPMS_COMMAND_PARAMS_GET_CAPABILITY        |   .parameters
TPM_CAP                                   |   |   .capability                            00000006             TPM_CAP.TPM_PROPERTIES
UINT32                                    |   |   .property                              0000012c             300
UINT32                                    |   |   .propertyCount                         00000001             1
Response                                  .
TPM_ST                                    |   .tag                                       8001                 TPM_ST.NO_SESSIONS
UINT32                                    |   .responseSize                              0000001b             27
TPM_RC                                    |   .responseCode                              00000000             TPM_RC.SUCCESS
TPMS_RESPONSE_HANDLES_GET_CAPABILITY      |   .handles
TPMS_RESPONSE_PARAMS_GET_CAPABILITY       |   .parameters
TPMI_YES_NO                               |   |   .moreData                              01                   1
TPMS_CAPABILITY_DATA                      |   |   .capabilityData
TPM_CAP                                   |   |   |   .capability                        00000006             TPM_CAP.TPM_PROPERTIES
TPMU_CAPABILITIES                         |   |   |   .data
TPML_TAGGED_TPM_PROPERTY                  |   |   |   |   .tpmProperties
UINT32                                    |   |   |   |   |   .count                     00000001             1
TPMS_TAGGED_PROPERTY                      |   |   |   |   |   .tpmProperty[0]
TPM_PT                                    |   |   |   |   |   |   .property              0000012c             TPM_PT.None
Warning: Parsed bad value for TPM_PT .parameters.capabilityData.data.tpmProperties.tpmProperty[0].property = 0x12c = 300 not in ValidValues(TPM_PT)
UINT32                                    |   |   |   |   |   |   .value                 00000300             768
Command                                   .
TPMI_ST_COMMAND_TAG                       |   .tag                                       8001                 TPMI_ST_COMMAND_TAG.NO_SESSIONS
UINT32                                    |   .commandSize                               0000000e             14
TPM_CC                                    |   .commandCode                               00000169             TPM_CC.NV_ReadPublic
TPMS_COMMAND_HANDLES_NV_READ_PUBLIC       |   .handles
TPMI_RH_NV_INDEX                          |   |   .nvIndex                               01c00002             TPM_HR.NV_INDEX.c00002
TPMS_COMMAND_PARAMS_NV_READ_PUBLIC        |   .parameters
Response                                  .
TPM_ST                                    |   .tag                                       8001                 TPM_ST.NO_SESSIONS
UINT32                                    |   .responseSize                              0000003e             62
TPM_RC                                    |   .responseCode                              00000000             TPM_RC.SUCCESS
TPMS_RESPONSE_HANDLES_NV_READ_PUBLIC      |   .handles
TPMS_RESPONSE_PARAMS_NV_READ_PUBLIC       |   .parameters
TPM2B_NV_PUBLIC                           |   |   .nvPublic
UINT16                                    |   |   |   .size                              000e                 14
TPMS_NV_PUBLIC                            |   |   |   .nvPublic
....

[maraino]

Didn't look too much into this PR, but we probably want to move these ports customizable.

[hslatman]

We could, but that wouldn't change much functionally. The PCAP is used just as a container in this case; we're not actually capturing traffic from/to those ports. The bytes read from and written to the TPM device are "massaged into network packets", so to say.