Checking hardware and firmware support for Flatcar Linux Trusted Computing¶
Trusted Computing requires support in both system hardware and firmware. This document specifies the required support and explains how to determine if a physical machine has the features needed to enable Trusted Computing in Flatcar Linux.
1. Check for Trusted Platform Module¶
Trusted Computing depends on the presence of a Trusted Platform Module (TPM). The TPM is a motherboard component responsible for storing the state of the system boot process, and providing a secure communication channel over which this state can be verified. To check for the presence of a TPM, install the latest Alpha version of Flatcar Linux and try to list the TPM device file in the
/sys system control filesystem:
# ls /sys/class/tpm/tpm0
If this returns an error, the system either does not have a TPM, or it is not enabled in the system firmware. Firmware configuration varies by system. Consult vendor documentation for details.
2. Check TPM version¶
Version 1.2 TPMs are currently supported. Read the TPM device ID file to discover the TPM version:
# cat /sys/class/tpm/tpm0/device/id
The contents of the
id file vary for supported version 1.2 TPMs. It is simplest to check that the file does not contain the known string for unsupported version 2.0 TPMs,
MSFT0101. Almost any other non-zero, non-error output from reading the
id file indicates a supported version 1.2 TPM.
Support for version 2.0 TPMs identified with the
MSFT0101 string will be added in a future Flatcar Linux release.
3. Check TPM is enabled and active¶
The TPM device provides control files in the
/sys filesystem, as seen above. Read the
active files to check TPM status:
# cat /sys/class/tpm/tpm0/device/enabled # cat /sys/class/tpm/tpm0/device/active
If either of these commands prints "0", reconfigure the TPM by writing a code for TPM activation at the next system boot to the PPI
# echo 6 > /sys/class/tpm/tpm0/device/ppi/request
Reboot the system and check TPM status again, as in Step 3.
4. Check boot measurement¶
The Flatcar Linux bootloader will record the state of boot components during the boot process — measuring each part, in TPM parlance, and storing the result in its Platform Configuration Registers (PCR). Verify that this measurement has been successful by reading the TPM device's
pcrs file, a textual representation of the contents of all PCRs:
# cat /sys/class/tpm/tpm0/device/pcrs
Boot component measurements are recorded in PCRs 9 through 13. These positions in
pcrs should all contain meaningful values; that is, values that are neither
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
A system that passes each of the above tests supports Flatcar Linux Trusted Computing and is actively measuring the boot process over the secure TPM channel.