On 10/19/23 18:21, Eddie James wrote:
Briefly describe the feature and specify the requirements.Signed-off-by: Eddie James <eaja...@linux.ibm.com> Reviewed-by: Simon Glass <s...@chromium.org> --- Changes since v12: - Add a bit of detail about OS usage and what pieces are measured doc/usage/index.rst | 1 + doc/usage/measured_boot.rst | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) create mode 100644 doc/usage/measured_boot.rst diff --git a/doc/usage/index.rst b/doc/usage/index.rst index 98b4719c40..bf53bb6bda 100644 --- a/doc/usage/index.rst +++ b/doc/usage/index.rst @@ -14,6 +14,7 @@ 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..0aad590859 --- /dev/null +++ b/doc/usage/measured_boot.rst @@ -0,0 +1,31 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Measured Boot +===================== + +U-Boot can perform a measured boot, the process of hashing various components +of the boot process, extending the results in the TPM and logging the +component's measurement in memory for the operating system to consume. + +By default, U-Boot will measure the operating system (linux) image, the
The OS image would mean the root file system? I guess you mean the loaded EFI binary here. Measured boot is not Linux specific. We should consider different scenarios: * U-Boot loading kernel, initrd, device-tree * U-Boot loading GRUB (or another boot manager), device-tree, GRUB loading initrd * U-Boot loading GRUB and passing a device-tree to GRUB, GRUB loading initrd and a new device-tree With the documentation the user should be enabled to understand what U-Boot measures in each of these cases. Please, observe that upstream GRUB uses LoadImage() while distros (e.g. Debian and Ubuntu) tend to bypass LoadImage(). Arent't there some other objects measured? - SMBIOS table - ACPI tables (still to be implemented) - EFI variables Best regards Heinrich
+initrd image, and the "bootargs" environment variable. By enabling +CONFIG_MEASURE_DEVICETREE, U-Boot will also measure the devicetree image. + +The operating system typically would verify that the hashes found in the +TPM PCRs match the contents of the event log. This can further be checked +against the hash results of previous boots. + +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.
