diff options
Diffstat (limited to 'Documentation/security')
-rw-r--r-- | Documentation/security/tpm/index.rst | 2 | ||||
-rw-r--r-- | Documentation/security/tpm/tpm_event_log.rst | 55 | ||||
-rw-r--r-- | Documentation/security/tpm/tpm_ftpm_tee.rst | 27 |
3 files changed, 84 insertions, 0 deletions
diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst index 3296533e54cf..fc40e9f23c85 100644 --- a/Documentation/security/tpm/index.rst +++ b/Documentation/security/tpm/index.rst @@ -4,5 +4,7 @@ Trusted Platform Module documentation .. toctree:: + tpm_event_log tpm_vtpm_proxy xen-tpmfront + tpm_ftpm_tee diff --git a/Documentation/security/tpm/tpm_event_log.rst b/Documentation/security/tpm/tpm_event_log.rst new file mode 100644 index 000000000000..f00f7a1d5e92 --- /dev/null +++ b/Documentation/security/tpm/tpm_event_log.rst @@ -0,0 +1,55 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +TPM Event Log +============= + +This document briefly describes what TPM log is and how it is handed +over from the preboot firmware to the operating system. + +Introduction +============ + +The preboot firmware maintains an event log that gets new entries every +time something gets hashed by it to any of the PCR registers. The events +are segregated by their type and contain the value of the hashed PCR +register. Typically, the preboot firmware will hash the components to +who execution is to be handed over or actions relevant to the boot +process. + +The main application for this is remote attestation and the reason why +it is useful is nicely put in the very first section of [1]: + +"Attestation is used to provide information about the platform’s state +to a challenger. However, PCR contents are difficult to interpret; +therefore, attestation is typically more useful when the PCR contents +are accompanied by a measurement log. While not trusted on their own, +the measurement log contains a richer set of information than do the PCR +contents. The PCR contents are used to provide the validation of the +measurement log." + +UEFI event log +============== + +UEFI provided event log has a few somewhat weird quirks. + +Before calling ExitBootServices() Linux EFI stub copies the event log to +a custom configuration table defined by the stub itself. Unfortunately, +the events generated by ExitBootServices() don't end up in the table. + +The firmware provides so called final events configuration table to sort +out this issue. Events gets mirrored to this table after the first time +EFI_TCG2_PROTOCOL.GetEventLog() gets called. + +This introduces another problem: nothing guarantees that it is not called +before the Linux EFI stub gets to run. Thus, it needs to calculate and save the +final events table size while the stub is still running to the custom +configuration table so that the TPM driver can later on skip these events when +concatenating two halves of the event log from the custom configuration table +and the final events table. + +References +========== + +- [1] https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/ +- [2] The final concatenation is done in drivers/char/tpm/eventlog/efi.c diff --git a/Documentation/security/tpm/tpm_ftpm_tee.rst b/Documentation/security/tpm/tpm_ftpm_tee.rst new file mode 100644 index 000000000000..8c2bae16e3d9 --- /dev/null +++ b/Documentation/security/tpm/tpm_ftpm_tee.rst @@ -0,0 +1,27 @@ +============================================= +Firmware TPM Driver +============================================= + +This document describes the firmware Trusted Platform Module (fTPM) +device driver. + +Introduction +============ + +This driver is a shim for firmware implemented in ARM's TrustZone +environment. The driver allows programs to interact with the TPM in the same +way they would interact with a hardware TPM. + +Design +====== + +The driver acts as a thin layer that passes commands to and from a TPM +implemented in firmware. The driver itself doesn't contain much logic and is +used more like a dumb pipe between firmware and kernel/userspace. + +The firmware itself is based on the following paper: +https://www.microsoft.com/en-us/research/wp-content/uploads/2017/06/ftpm1.pdf + +When the driver is loaded it will expose ``/dev/tpmX`` character devices to +userspace which will enable userspace to communicate with the firmware TPM +through this device. |