On 10/19/23 18:21, Eddie James wrote:
Briefly describe the feature and specify the requirements.
Signed-off-by: Eddie James eajames@linux.ibm.com Reviewed-by: Simon Glass sjg@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.