tpm2_policyrestart man page

tpm2_policyrestart(1) — Restart an existing session with the TPM.

Synopsis

tpm2_policyrestart [Options]

Description

tpm2_policyrestart(1) - Restarts a session with the TPM back to it's initial state. This is useful when the TPM gives one a TPM_RC_PCR_CHANGED (0x00000128) error code when using a PCR policy session.

This will be returned if a PCR state affecting policy is altered during the session. One could restart the session and try again, however, the PCR state would still need to satisfy the policy.

Options

References

Common Options

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

TCTI Configuration

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:

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.

TCTI Defaults

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. The tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. You can query what TCTI will be chosen as the default by using the -v option to print the version information. The "default-tcti" key-value pair will indicate which of the aforementioned TCTIs is the default.

Custom TCTIs

Any TCTI that implements the dynamic TCTI interface can be loaded. The tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. Thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics.

Tcti Options

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

Examples

Start a policy session and restart it, unsealing some data.

# create a policy and bind it to an object
tpm2_startauthsession -S session.dat

tpm2_policypcr -S session.dat -l "sha1:0,1,2,3" -L policy.dat

tpm2_createprimary -c primary.ctx

tpm2_create -Cprimary.ctx -u key.pub -r key.priv -L policy.dat -i- <<< "secret"

tpm2_load -C primary.ctx -c key.ctx -u key.pub -r key.priv

tpm2_flushcontext session.dat

# satisfy the policy and use the object
tpm2_startauthsession --policy -S session.dat

tpm2_policypcr -S session.dat -l "sha1:0,1,2,3"

# PCR event occurs here causing unseal to fail
tpm2_pcrevent 0 <<< "event data"

tpm2_unseal -psession:session.dat -c key.ct
ERROR: Esys_Unseal(0x128) - tpm:error(2.0): PCR have changed since checked

# Clear the policy digest to initial state, note access to object no longer allowed by
# policy so policyor would be useful here.
tpm2_policyrestart -S session.dat

Returns

Tools can return any of the following codes:

Limitations

It expects a session to be already established via tpm2_startauthsession(1) and requires one of the following:

Without it, most resource managers will not save session state between command invocations.

Bugs

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

Help

See the Mailing List (https://lists.01.org/mailman/listinfo/tpm2)

Info

tpm2-tools General Commands Manual