tpm2_pcrread - Man Page

tpm2_pcrread [Options] PCR_LIST_OR_ALG

tpm2_pcrread(1) - Displays PCR values. Without any arguments, tpm2_pcrread(1) outputs all PCRs and their hash banks. One can use specify the hash algorithm or a pcr list as an argument to filter the output.

To only output PCR banks with a given algorithm, specify the hashing algorithm as the argument. Algorithms should follow the “formatting standards”, see section “Algorithm Specifiers”. Also, see section “Supported Hash Algorithms” for a list of supported hash algorithms.

To output a list of PCR banks (sha1, sha256, etc) and ids (0, 1, 2 etc) specify a PCR selection list as the argument as specified via section “PCR Bank Specifiers”.

Also read Notes section below.

Output is written in a YAML format to stdout, with each algorithm followed by a PCR index and its value. As a simple example assume just sha1 and sha256 support and only 1 PCR. The output would be:

$ tpm2_pcrread sha1:0+sha256:0
sha1 :
  0  : 0000000000000000000000000000000000000003
sha256 :
  0  : 0000000000000000000000000000000000000000000000000000000000000003

• -o, --output=FILE:

  The output file to write the PCR values in binary format, optional.

• --cphash=FILE

  File path to record the hash of the command parameters. This is commonly termed as cpHash. NOTE: When this option is selected, The tool will not actually execute the command, it simply returns a cpHash.

• -F, --pcrs_format=FORMAT:

  Format selection for the binary blob in the PCR output file. `values' will output a binary blob of the PCR values. `serialized' will output a binary blob of the PCR values in the form of serialized data structure in little endian format. Optional. Default is `values'.

This collection of options are common to many programs and provide information that many users may expect.

• -h, --help=[man|no-man]: Display the tools manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the “man” option argument is specified, however if explicit “man” is requested, the tool will provide errors from man on stderr. If the “no-man” option if specified, or the manpager fails, the short options will be output to stdout.

  To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details.

• -v, --version: Display version information for this tool, supported tctis and exit.
• -V, --verbose: Increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed.
• -Q, --quiet: Silence normal tool output to stdout.
• -Z, --enable-errata: Enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent.
• -R, --autoflush: Enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is is set to yes or true.

The TCTI or “Transmission Interface” is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums.

To control the TCTI, the tools respect:

1. The command line option -T or --tcti
2. The environment variable: TPM2TOOLS_TCTI.

Note: The command line option always overrides the environment variable.

The current known TCTIs are:

• tabrmd - The resource manager, called tabrmd (https://github.com/tpm2-software/tpm2-abrmd). Note that tabrmd and abrmd as a tcti name are synonymous.
• mssim - Typically used for communicating to the TPM software simulator.
• device - Used when talking directly to a TPM device file.
• none - Do not initalize a connection with the TPM. Some tools allow for off-tpm options and thus support not using a TCTI. Tools that do not support it will error when attempted to be used without a TCTI connection. Does not support ANY options and MUST BE presented as the exact text of “none”.

The arguments to either the command line option or the environment variable are in the form:

<tcti-name>:<tcti-option-config>

Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively.

This collection of options are used to configure the various known TCTI modules available:

• device: For the device TCTI, the TPM character device file for use by the device TCTI can be specified. The default is /dev/tpm0.

  Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”

• mssim: For the mssim TCTI, the domain name or IP address and port number used by the simulator can be specified. The default are 127.0.0.1 and 2321.

  Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”

• abrmd: For the abrmd TCTI, the configuration string format is a series of simple key value pairs separated by a `,' character. Each key and value string are separated by a `=' character.

  • TCTI abrmd supports two keys:

    1. `bus_name' : The name of the tabrmd service on the bus (a string).
    2. `bus_type' : The type of the dbus instance (a string) limited to `session' and `system'.

  Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:

  \--tcti=tabrmd:bus_name=com.example.FooBar

  Specify the default (abrmd) tcti and a config string of bus_type=session:

  \--tcti:bus_type=session

  NOTE: abrmd and tabrmd are synonymous.

PCR bank specifiers

Supported hash algorithms are:

• 0x4 or sha1 for TPM_ALG_SHA1
• 0xB or sha256 for TPM_ALG_SHA256 (default)
• 0xC or sha384 for TPM_ALG_SHA384
• 0xD or sha512 for TPM_ALG_SHA512
• 0x12 or sm3_256 for TPM_ALG_SM3_256

NOTE: Your TPM may not support all algorithms.

Options that take algorithms support “nice-names”.

There are two major algorithm specification string classes, simple and complex. Only certain algorithms will be accepted by the TPM, based on usage and conditions.

The maximum number of PCR that can be dumped at once is associated with the maximum length of a bank.

On most TPMs, it means that this tool can dump up to 24 PCRs at once.

Tools can return any of the following codes:

• 0 - Success.
• 1 - General non-specific error.
• 2 - Options handling error.
• 3 - Authentication error.
• 4 - TCTI related error.
• 5 - Non supported scheme. Applicable to tpm2_testparams.

Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)

See the Mailing List (https://lists.linuxfoundation.org/mailman/listinfo/tpm2)

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