tpm2_policynv - Man Page

Evaluates policy authorization by comparing a specified value against the contents in the specified NV Index.

Synopsis

tpm2_policynv [Options] [ARGUMENT] [ARGUMENT]

Description

tpm2_policynv(1) - This command evaluates policy authorization by comparing the contents written to an NV index against the one specified in the tool options. The tool takes two arguments - (1) The NV index specified as raw handle or an offset value to the nv handle range "TPM2_HR_NV_INDEX" and (2) Comparison operator for magnitude comparison and or bit test operations. In the specification the NV index holding the data is called operandA and the data that the user specifies to compare is called operandB. The comparison operator can be specified as follows: * "eq" if operandA = operandB * "neq" if operandA != operandB * "sgt" if signed operandA > signed operandB * "ugt" if unsigned operandA > unsigned operandB * "slt" if signed operandA < signed operandB * "ult" if unsigned operandA < unsigned operandB * "sge" if signed operandA >= signed operandB * "uge" if unsigned operandA >= unsigned operandB * "sle" if signed operandA <= unsigned operandB * "ule" if unsigned operandA <= unsigned operandB * "bs" if all bits set in operandA are set in operandB * "bc" if all bits set in operandA are clear in operandB

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

Test if NV index content value is equal to an input number. To do this we first create an NV index of size 1 byte and write a value. Eg. 0xAA. Next we attempt to create a policy that becomes valid if the equality comparison operation of the NV index content against the one specified in the tool options.

Define the test NV Index and write the value 0xAA to it

nv_test_index=0x01500001
tpm2_nvdefine -C o -p nvpass $nv_test_index -a "authread|authwrite" -s 1
echo "aa" | xxd -r -p | tpm2_nvwrite -P nvpass -i- $nv_test_index

Attempt defining policynv with wrong comparison value specified in

options.

tpm2_startauthsession -S session.ctx --policy-session
### This should fail
echo 0xBB | tpm2_policynv -S session.ctx -L policy.nv -i- 0x1500001 eq -P nvpass
tpm2_flushcontext session.ctx

Attempt defining policynv with right comparison value specified in

options.

tpm2_startauthsession -S session.ctx --policy-session
### This should pass
echo 0xAA | tpm2_policynv -S session.ctx -L policy.nv -i- 0x1500001 eq -P nvpass
tpm2_flushcontext session.ctx

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