doc: describe UEFI measured boot
We currently only describe the process to enable measured boot using
bootm. Describe the UEFI requirements as well which predate bootm.
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/usage/measured_boot.rst b/doc/usage/measured_boot.rst
index 9691904..05c439e 100644
--- a/doc/usage/measured_boot.rst
+++ b/doc/usage/measured_boot.rst
@@ -7,19 +7,46 @@
of the boot process, extending the results in the TPM and logging the
component's measurement in memory for the operating system to consume.
+The functionality is available when booting via the EFI subsystem or 'bootm'
+command.
+
+UEFI measured boot
+------------------
+
+The EFI subsystem implements the `EFI TCG protocol
+<https://trustedcomputinggroup.org/resource/tcg-efi-protocol-specification/>`_
+and the `TCG PC Client Specific Platform Firmware Profile Specification
+<https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/>`_
+which defines the binaries to be measured and the corresponding PCRs to be used.
+
+Requirements
+~~~~~~~~~~~~
+
+* A hardware TPM 2.0 supported by an enabled U-Boot driver
+* CONFIG_EFI_TCG2_PROTOCOL=y
+* CONFIG_EFI_TCG2_PROTOCOL_EVENTLOG_SIZE=y
+* optional CONFIG_EFI_TCG2_PROTOCOL_MEASURE_DTB=y will measure the loaded DTB
+ in PCR 1
+
+Legacy measured boot
+--------------------
+
+The commands booti, bootm, and bootz can be used for measured boot
+using the legacy entry point of the Linux kernel.
+
By default, U-Boot will measure the operating system (linux) image, the
initrd image, and the "bootargs" environment variable. By enabling
-CONFIG_MEASURE_DEVICETREE, U-Boot will also measure the devicetree image.
+CONFIG_MEASURE_DEVICETREE, U-Boot will also measure the devicetree image in PCR1.
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
+* A hardware TPM 2.0 supported by an enabled U-Boot driver
+* CONFIG_TPMv2=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
