[PATCH v14 4/8] bootm: Support boot measurement

[Heinrich Schuchardt]

On 24.10.23 17:43, Eddie James wrote:
> Add a configuration option to measure the boot through the bootm
> function. Add the measurement state to the booti and bootz paths
> as well.
>
> Signed-off-by: Eddie James <eajames at linux.ibm.com>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> ---
> Changes since v8:
>   - Added a configuration option to select to ignore any existing
>     event log. This would only be selected for systems that know
>     that U-Boot is the first stage bootloader. This is necessary
>     because the reserved memory region may persist through resets
>     and so U-Boot attempts to append to the previous boot's log.
>
> Changes since v6:
>   - Added comment for bootm_measure
>   - Fixed line length in bootm_measure
>
>   boot/Kconfig    | 32 +++++++++++++++++++++
>   boot/bootm.c    | 74 +++++++++++++++++++++++++++++++++++++++++++++++++
>   cmd/booti.c     |  1 +
>   cmd/bootm.c     |  2 ++
>   cmd/bootz.c     |  1 +
>   include/bootm.h | 11 ++++++++
>   include/image.h |  1 +
>   7 files changed, 122 insertions(+)
>
> diff --git a/boot/Kconfig b/boot/Kconfig
> index a01e6cb8aa..abbc72f4cf 100644
> --- a/boot/Kconfig
> +++ b/boot/Kconfig
> @@ -685,6 +685,38 @@ config LEGACY_IMAGE_FORMAT
>   	  loaded. If a board needs the legacy image format support in this
>   	  case, enable it here.
>
> +config MEASURED_BOOT
> +	bool "Measure boot images and configuration to TPM and event log"
> +	depends on HASH && TPM_V2
> +	help
> +	  This option enables measurement of the boot process. Measurement
> +	  involves creating cryptographic hashes of the binary images that
> +	  are booting and storing them in the TPM. In addition, a log of
> +	  these hashes is stored in memory for the OS to verify the booted
> +	  images and configuration. Enable this if the OS has configured
> +	  some memory area for the event log and you intend to use some
> +	  attestation tools on your system.
> +
> +if MEASURED_BOOT
> +	config MEASURE_DEVICETREE
> +	bool "Measure the devicetree image"
> +	default y if MEASURED_BOOT
> +	help
> +	  On some platforms, the devicetree is not static as it may contain
> +	  random MAC addresses or other such data that changes each boot.
> +	  Therefore, it should not be measured into the TPM. In that case,
> +	  disable the measurement here.

I guess the device-tree should be measured before fix-ups.

A main source of randomness is the KASLR seed.

@Ilias: How are we handling this in the EFI case?

Best regards

Heinrich