[PATCH v8 6/6] doc: Add measured boot documentation

[Heinrich Schuchardt]

On 3/3/23 20:25, Eddie James wrote:
> Briefly describe the feature and specify the requirements.
>
> Signed-off-by: Eddie James <eajames at linux.ibm.com>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> ---
>   doc/usage/index.rst         |  1 +
>   doc/usage/measured_boot.rst | 23 +++++++++++++++++++++++
>   2 files changed, 24 insertions(+)
>   create mode 100644 doc/usage/measured_boot.rst
>
> diff --git a/doc/usage/index.rst b/doc/usage/index.rst
> index 840c20c934..1cb6988d8a 100644
> --- a/doc/usage/index.rst
> +++ b/doc/usage/index.rst
> @@ -12,6 +12,7 @@ Use U-Boot
>      partitions
>      cmdline
>      semihosting
> +   measured_boot
>
>   Shell commands
>   --------------
> diff --git a/doc/usage/measured_boot.rst b/doc/usage/measured_boot.rst
> new file mode 100644
> index 0000000000..8357b1f480
> --- /dev/null
> +++ b/doc/usage/measured_boot.rst
> @@ -0,0 +1,23 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Measured Boot
> +=====================
> +
> +U-Boot can perform a measured boot, the process of hashing various components

This text is misleading: U-Boot does not perform measured boot.

U-Boot performing measured boot would imply that it checks if the
incoming values of the PCRs match expected values. This is not what is
done with this series.

U-Boot assists measured boot by extending PCRs and providing an event log.

Best regards

Heinrich

> +of the boot process, extending the results in the TPM and logging the
> +component's measurement in memory for the operating system to consume.
> +
> +Requirements
> +---------------------
> +
> +* A hardware TPM 2.0 supported by the U-Boot drivers
> +* CONFIG_TPM=y
> +* CONFIG_MEASURED_BOOT=y
> +* Device-tree configuration of the TPM device to specify the memory area
> +  for event logging. The TPM device node must either contain a phandle to
> +  a reserved memory region or "linux,sml-base" and "linux,sml-size"
> +  indicating the address and size of the memory region. An example can be
> +  found in arch/sandbox/dts/test.dts
> +* The operating system must also be configured to use the memory regions
> +  specified in the U-Boot device-tree in order to make use of the event
> +  log.