Re: [PATCH v5 2/5] tsm-mr: Add tsm-mr sample code

This sample kernel module demonstrates how to make MRs accessible to user
mode through the tsm-mr library.

Once loaded, this module registers a `miscdevice` that host a set of
emulated measurement registers as shown in the directory tree below.

/sys/class/misc/tsm_mr_sample
└── mr
    ├── config_mr
    ├── report_digest:sha512
    ├── rtmr0:sha256
    ├── rtmr1:sha384
    ├── rtmr_crypto_agile:sha256
    ├── rtmr_crypto_agile:sha384
    └── static_mr:sha384

Among the MRs in this example:

- `config_mr` demonstrates a hashless MR, like MRCONFIGID in Intel TDX or
  HOSTDATA in AMD SEV.
- `static_mr` demonstrates a static MR. The suffix `:sha384` indicates its
  value is a sha384 digest.
- `rtmr0` is an RTMR with `TSM_MR_F_WRITABLE` **cleared**, preventing
  direct extensions; as a result, the attribute `rtmr0:sha256` is
  read-only.
- `rtmr1` is an RTMR with `TSM_MR_F_WRITABLE` **set**, permitting direct
  extensions; thus, the attribute `rtmr1:sha384` is writable.
- `rtmr_crypto_agile` demonstrates a "single" MR that supports multiple
  hash algorithms. Each supported algorithm has a corresponding digest,
  usually referred to as a "bank" in TCG terminology. In this specific
  sample, the 2 banks are aliased to `rtmr0` and `rtmr1`, respectively.
- `report_digest` contains the digest of the internal report structure
  living in this sample module's memory. It is to demonstrate the use of
  the `TSM_MR_F_LIVE` flag. Its value changes each time an RTMR is
  extended.

Signed-off-by: Cedric Xing <redacted>
---
 MAINTAINERS                    |   1 +
 samples/Kconfig                |  11 ++++
 samples/Makefile               |   1 +
 samples/tsm-mr/Makefile        |   2 +
 samples/tsm-mr/tsm_mr_sample.c | 137 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 152 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 1d1426af3a68..fd5bbf78ec8b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -24618,6 +24618,7 @@ S:	Maintained
 F:	Documentation/ABI/testing/configfs-tsm
 F:	drivers/virt/coco/tsm*.c
 F:	include/linux/tsm*.h
+F:	samples/tsm/*
 
 TRUSTED SERVICES TEE DRIVER
 M:	Balint Dobszay <balint.dobszay@arm.com>

diff --git a/samples/Kconfig b/samples/Kconfig
index 09011be2391a..6ade17cb16b4 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig

@@ -184,6 +184,17 @@ config SAMPLE_TIMER
 	bool "Timer sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
 
+config SAMPLE_TSM_MR
+	tristate "TSM measurement sample"
+	select TSM_MEASUREMENTS
+	select VIRT_DRIVERS
+	help
+	  Build a sample module that emulates MRs (Measurement Registers) and
+	  exposes them to user mode applications through the TSM sysfs
+	  interface (/sys/class/misc/tsm_mr_sample/emulated_mr/).
+
+	  The module name will be tsm-mr-sample when built as a module.
+
 config SAMPLE_UHID
 	bool "UHID sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL

diff --git a/samples/Makefile b/samples/Makefile
index bf6e6fca5410..c95bac31851c 100644
--- a/samples/Makefile
+++ b/samples/Makefile

@@ -43,3 +43,4 @@ obj-$(CONFIG_SAMPLES_RUST)		+= rust/
 obj-$(CONFIG_SAMPLE_DAMON_WSSE)		+= damon/
 obj-$(CONFIG_SAMPLE_DAMON_PRCL)		+= damon/
 obj-$(CONFIG_SAMPLE_HUNG_TASK)		+= hung_task/
+obj-$(CONFIG_SAMPLE_TSM_MR)		+= tsm-mr/

diff --git a/samples/tsm-mr/Makefile b/samples/tsm-mr/Makefile
new file mode 100644
index 000000000000..587c3947b3a7
--- /dev/null
+++ b/samples/tsm-mr/Makefile

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_TSM_MR) += tsm_mr_sample.o

diff --git a/samples/tsm-mr/tsm_mr_sample.c b/samples/tsm-mr/tsm_mr_sample.c
new file mode 100644
index 000000000000..3ee35d87d275
--- /dev/null
+++ b/samples/tsm-mr/tsm_mr_sample.c

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2024 Intel Corporation. All rights reserved. */