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swtpm(8) swtpm(8)

NAME

swtpm - TPM Emulator for TPM 1.2 and 2.0

SYNOPSIS

swtpm socket [OPTIONS]

swtpm chardev [OPTIONS]

swtpm cuse [OPTIONS]

DESCRIPTION

swtpm implements a TPM software emulator built on libtpms. It provides access to TPM functionality over a TCP/IP socket interface or it can listend for commands on a character device, or create a CUSE (character device in userspace) interface for receiving of TPM commands.

Unless corresponding command line parameters are used, the swtpm socket version requires that the environment variable TPM_PORT be set to the TCP/IP port the process is supposed to listen on for TPM request messages.

Similarly, the environment variable TPM_PATH can be set and contain the name of a directory where the TPM can store its persistent state into.

The swtpm process can be gracefully terminated by sending a SIGTERM signal to it.

The swtpm cuse version requires root rights to start the TPM.

Options for socket interface

The following options are supported if the socket interface is chosen:

Use the given port rather than using the environment variable TPM_PORT.
Terminate the TPM after the client has closed the data channel connection (TCP only).
Expect TCP connections on the given port; if a port is not provided a file descriptor must be passed with the fd parameter and the commands are read from this file descriptor then. If a port is provided the bind address on which to listen for TCP connections can be provided as well; the default bind address is 127.0.0.1. If a link local IPv6 address is provided, the name of the interface to bind to must be provided with ifname.

This parameter enables a persistent connection by default unless the disconnect option is given. This parameter should be used rather than the -p and --fd options.

Expect UnixIO connections on the given path. If no path is provided, a file descriptor must be passed instead. The mode parameter allows a user to set the file mode bits of the UnixIO path. The mode bits value must be given as an octal number starting with a '0'. The default value is 0770. uid and gid set the ownership of the UnixIO socket's path. This operation requires root privileges.

Options for character device interface

The following options are supported if the chardev interface is chosen:

Use the given device to listen for TPM commands and send response on.
Create a Linux vTPM proxy device instance and read TPM commands from its backend device.

Options for the CUSE interface

The following options are supported if the cuse interface is chosen:

The TPM will use a device with the given name. A device with the given name will be created in /dev. This is a mandatory option.
Create the device with the given major number.
Create the device with the given minor number.

Options for socket and character device interfaces:

The following options are supported by the socket and character device interfaces:

Use the given socket file descriptor or character device file descriptor for receiving TPM commands and sending responses. For the socket interface, this option automatically assumes -t.
Daemonize the process.
This option adds a control channel to the TPM. The control channel can either use a UnixIO socket with a given path or filedescriptor or it can use a TCP socket on the given port or filedescriptor. If a port is provided the bind address on which to listen for TCP connections can be provided as well; the default bind address is 127.0.0.1. If a link local IPv6 address is provided, the name of the interface to bind to must be provided with ifname.

The mode parameter allows a user to set the file mode bits of the UnixIO path. The mode bits value must be given as an octal number starting with a '0'. The default value is 0770. uid and gid set the ownership of the UnixIO socket's path. This operation requires root privileges.

The terminate parameter enables the automatic termination of swtpm when the control channel connection has been lost. This is useful in scenarios where the control channel connection is held permanently, such as by QEMU, and swtpm should terminate upon abnormal termination of the client that could not send a CMD_SHUTDOWN via the control channel anymore.

The control channel enables out-of-band control of the TPM, such as resetting the TPM.

Options for all interfaces

The following options are support by all interfaces:

Use the given path rather than using the environment variable TPM_PATH.

If dir is specified, the TPM state files will be written to the dir with the given file mode bits. This value must be given as an octal number starting with a '0'. The default value is 0640.

If backend-uri is specified, the TPM state data will be stored to the URI. Currently backend-uri=dir://<path_to_dir> and backend-uri=file://<path_to_dir> are available. For 'dir://', the URI should specify the path to the directory where files are stored. If path_to_dir starts with a '/' then the path is interpreted as an absolute path, otherwise it is a path relative to the current directory. For 'file://', the URI should specify a single file or block device where TPM state will be stored. A blockdevice must exist already and be big enough to store all state. (since v0.7)

Choose TPM 2 functionality; by default a TPM 1.2 is chosen.
Enable logging to a file given its file descriptor or its path. Use '-' for path to suppress the logging.

The level parameter allows a user to choose the level of logging. Starting at log level 5, libtpms debug logging is activated.

All logged lines will be prefixed with prefix. By default no prefix is prepended.

If truncate is passed, the log file will be truncated.

The reject-locality-4 parameter will cause TPM error messages to be returned for requests to set the TPM into locality 4.

The allow-set-locality parameter allows the swtpm to receive TPM/TPM2_SetLocality commands. This is parameter is useful if the Linux VTPM proxy driver access is enabled by file descriptor passing. This option is implied by the --vtpm-proxy option and therefore need not be explicitly set if this option is passed. In all other cases care should be taken as to who can send the TPM/TPM2_SetLocality command.

Enable encryption of the state files of the TPM. The keyfile must contain an AES key of supported size; 128 bit (16 bytes) and 256 bit (32 bytes) keys are supported.

The key may be in binary format, in which case the file size must be 16 or 32 bytes. If the key is in hex format (default), the key may consist of 32 or 64 hex digits starting with an optional '0x'.

The mode parameter indicates which block chaining mode is to be used. Currently aes-cbc (aes-128-cbc) and aes-256-cbc are supported. The encrypted data is integrity protected using encrypt-then-mac.

The remove parameter will attempt to remove the given keyfile once the key has been read.

This variant of the key parameter allows a user to provide a passphrase in a file. The file is read and a key is derived from it using either a SHA512 hash or PBKDF2. By default PBKDF2 is used.
The availability of a migration key ensures that the state of the TPM will not be revealed in unencrypted form when the TPM state blobs are retrieved through the ioctl interface. The migration key is not used for encrypting TPM state written to files, this is what the --key parameter is used for.

The migration key and the key used for encrypting the TPM state files may be the same.

While the key for the TPM state files needs to stay with those files it encrypts, the migration key needs to stay with the TPM state blobs. If for example the state of the TPM is migrated between hosts in a data center, then the TPM migration key must be available at all the destinations, so in effect it may have to be a key shared across all machines in the datacenter. In contrast to that, the key used for encrypting the TPM state files can be different for each TPM and need only be available on the host where the TPM state resides.

The migration key enables the encryption of the TPM state blobs. The keyfile must contain an AES key of supported size; 128 bit (16 bytes) and 256 bit (32 bytes) keys are supported.

The key may be in binary format, in which case the file size must be 16 or 32 bytes. If the key is in hex format (default), the key may consist of 32 or 64 hex digits starting with an optional '0x'.

The mode parameter indicates which block chaining mode is to be used. Currently aes-cbc (aes-128-cbc) and aes-256-cbc are supported. The encrypted data is integrity protected using encrypt-then-mac.

The remove parameter will attempt to remove the given keyfile once the key has been read.

This variant of the key parameter allows a user to provide a passphrase in a file. The file is read and a key is derived from it using either a SHA512 hash or PBKDF2. By default PBKDF2 is used.
This options allows a user to set the name of file where the process ID (pid) of the TPM will be written into. It is also possible to pass a file descriptor to a file that has been opened for writing.
Switch to the given user. This option can only be used when swtpm is started as root.
Chroot to the given directory at startup. This option can only be used when swtpm is started as root.
This option allows a user to select the action to take by the seccomp profile when a syscall is executed that is not allowed. The default is kill. To disable the seccomp profile, choose none. The log action logs offending syscalls. The log action is only available if libseccomp supports logging.

This option is only available on Linux and only if swtpm was compiled with libseccomp support.

The not-need-init flag enables the TPM to accept TPM commands right after start without requiring an INIT to be sent to it through the command channel (see the '-i' option of swtpm_ioctl).

The startup options cause a TPM_Startup or TPM2_Startup command to automatically be sent. The startup-deactivated option is only valid for a TPM 1.2. These options imply not-need-init, except for the startup-none option, which results in no command being sent.

If --vtpm-proxy is used, startup-clear is automatically chosen but this can be changed with this option.

The disable-auto-shutdown flag prevents swtpm from automatically sending a TPM2_Shutdown() before the reset of a TPM 2 or before the swtpm process is terminated. When this flag is not provide swtpm will send this command to avoid increasing the dictionary attack (DA) lockout counter and ulimately a DA lockout by the TPM 2 due to omission of sending a required TPM2_Shutdown() before TPM 2 reset or swtpm process termination.

Print capabilities that were added to swtpm after version 0.1. The output may contain the following: 

    {
      "type": "swtpm",
      "features": [
        "tpm-1.2",
        "tpm-2.0",
        "cmdarg-seccomp",
        "cmdarg-key-fd",
        "cmdarg-pwd-fd",
        "cmdarg-print-states",
        "cmdarg-chroot",
        "cmdarg-migration",
        "nvram-backend-dir",
        "nvram-backend-file",
        "tpm-send-command-header",
        "flags-opt-startup",
        "flags-opt-disable-auto-shutdown",
        "rsa-keysize-1024",
        "rsa-keysize-2048",
        "rsa-keysize-3072"
      ],
      "version": "0.7.0"
    }

The version field is available since v0.7.

The meaning of the feature verbs is as follows:

TPM 1.2 emulation is supported (libtpms is compiled with 1.2 support).
TPM 2 emulation is supported (libtpms is compiled with 2.0 support).

(the --tpm2 option is supported)

The --seccomp option is supported.
The --key option supports the fd= parameter.
The --key option supports the pwdfd= parameter.
The --print-states option is supported.
The --chroot option is supported.
The --migration option is supported.
The --tpmstate option supports the backend-uri=dir://... parameter.
The --tpmstate option supports the backend-uri=file://... parameter.
The TPM 2 commands may be prefixed by a header that carries a 4-byte command, 1 byte for locality, and 4-byte TPM 2 command length indicator. The TPM 2 will respond by preprending a 4-byte response indicator and a 4-byte trailer. All data is sent in big endian format.
The --flags option supports the startup-... options.
The --flags option supports the disable-auto-shutdown flag.
The TPM 2 supports the shown RSA key sizes. If none of the rsa-keysize verbs is shown then only RSA 2048 bit keys are supported.
This option allows to print out the TPM 1.2 or TPM 2 state blobs that are currently stored in a storage backend. This option requires that the storage backend be specified using the --tpmstate option and if TPM 2 state blobs are supposed to be shown, the --tpm2 option must be passed.

The following shows the JSON output of this option. It indicates that the 'permall' and 'volatile' states are available.

    {
      "type": "swtpm",
      "states": [
        {
          "name": "permall",
          "size": 6013
        }, {
          "name": "volatile",
          "size": 1087
        }
      ]
    }
This option allows to control the locking of the NVRAM storage for the purpose of supporting migration between hosts that have shared storage setup for the swtpm's state directory and if locking is supported by the storage backend. The directory storage backend for example supports locking and therefore requires usage of this option in case of shared storage. When providing the incoming option parameter swtpm defers the locking of the NVRAM until the state blobs are received or until the first TPM command is processed if no state blobs were received. The release-lock-outgoing option parameter causes swtpm to release any NVRAM lock once the TPM's 'savestate' blob is received from swtpm. To avoid releasing the lock too early the 'permanent' and 'volatile' state blobs must be received before the 'savestate' blob.
Display usage info.

NOTES

If a TPM 2 is used, the user is typically required to send a TPM2_Shutdown() command to a TPM 2 to avoid possibly increasing the TPM_PT_LOCKOUT_COUNTER that may lead to a dictionary attack (DA) lockout upon next startup (TPM2_Startup()) of the TPM 2. Whether the TPM_PT_LOCKOUT_COUNTER is increased depends on previous commands sent to the TPM 2 as well as internal state of the TPM 2. One example that will trigger the counter to increase is the omission of a password when trying to access a password-protected object or NVRAM location that has the DA attribute set, followed by termination of swtpm without sending TPM2_Shutdown(). To avoid a DA lockout swtpm will make a best-effort and send a TPM2_Shutdown(SU_STATE) or TPM2_Shutdown(SU_CLEAR) if found necessary.

SEE ALSO

swtpm_bios, swtpm_cuse

2022-11-22 swtpm