Merge tag 'tpm-next-27102023' of https://source.denx.de/u-boot/custodians/u-boot-tpm

bootX measurements and measurement API moved to u-boot core:

Up to now, U-Boot could perform measurements and EventLog creation as
described by the TCG spec when booting via EFI.

The EFI code was residing in lib/efi_loader/efi_tcg2.c and contained
both EFI specific code + the API needed to access the TPM, extend PCRs
and create an EventLog. The non-EFI part proved modular enough and
moving it around to the TPM subsystem was straightforward.

With that in place we can have a common API for measuring binaries
regardless of the boot command, EFI or boot(m|i|z), and contructing an
EventLog.

I've tested all of the EFI cases -- booting with an empty EventLog and
booting with a previous stage loader providing one and found no
regressions.  Eddie tested the bootX part.

Eddie also fixed the sandbox TPM which couldn't be used for the EFI code
and it now supports all the required capabilities. This had a slight
sideeffect in our testing since the EFI subsystem initializes the TPM
early and 'tpm2 init' failed during some python tests. That code only
opens the device though, so we can replace it with 'tpm2 autostart'
which doesn't error out and still allows you to perfom the rest of the
tests but doesn't report an error if the device is already opened.

There's a few minor issues with this PR as well but since testing and
verifying the changes takes a considerable amount of time, I prefer
merging it now.

Heinrich has already sent a PR for -master containing "efi_loader: fix
EFI_ENTRY point on get_active_pcr_banks" and I am not sure if that will
cause any conflicts, but in any case they should be trivial to resolve.

Both the EFI and non-EFI code have a Kconfig for measuring the loaded
Device Tree.  The reason this is optional is that we can't reason
when/if devices add random info like kaslr-seed, mac addresses etc in
the DT. In that case measurements are random, board specific and
eventually useless.  The reason it was difficult to fix it prior to this
patchset is because the EFI subsystem and thus measurements was brought
up late and DT fixups might have already been applied. With this
patchset we can measure the DT really early in the future.

Heinrich also pointed out that the two Kconfigs for the DTB measurements
can be squashed in a single one and that the documentation only explains
the non-EFI case.  I agree on both but as I said this is a sane working
version, so let's pull this first it's aleady big enough and painful to
test.

2 files changed, 32 insertions, 0 deletions

diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 839589c2147..d8e23fcacff 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 00000000000..0aad5908590
--- /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
+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.