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

Cedric Xing
2025-04-24T20:12:58Z

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 <cedric.xing@intel.com>
---
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. */
+
+#define DEBUG
+#define pr_fmt(x) KBUILD_MODNAME ": " x
+
+#include <linux/module.h>
+#include <linux/tsm-mr.h>
+#include <linux/miscdevice.h>
+#include <crypto/hash.h>
+
+struct {
+ u8 static_mr[SHA384_DIGEST_SIZE];
+ u8 config_mr[SHA512_DIGEST_SIZE];
+ u8 rtmr0[SHA256_DIGEST_SIZE];
+ u8 rtmr1[SHA384_DIGEST_SIZE];
+ u8 report_digest[SHA512_DIGEST_SIZE];
+} sample_report = {
+ .static_mr = "static_mr",
+ .config_mr = "config_mr",
+ .rtmr0 = "rtmr0",
+ .rtmr1 = "rtmr1",
+};
+
+static int sample_report_refresh(const struct tsm_measurements *tm,
+ const struct tsm_measurement_register *mr)
+{
+ struct crypto_shash *tfm;
+ int rc;
+
+ pr_debug("%s(%s) is called\n", __func__, mr ? mr->mr_name : "<nil>");
+
+ tfm = crypto_alloc_shash(hash_algo_name[HASH_ALGO_SHA512], 0, 0);
+ if (IS_ERR(tfm)) {
+ pr_err("crypto_alloc_shash failed: %ld\n", PTR_ERR(tfm));
+ return PTR_ERR(tfm);
+ }
+
+ rc = crypto_shash_tfm_digest(tfm, (u8 *)&sample_report,
+ offsetof(typeof(sample_report),
+ report_digest),
+ sample_report.report_digest);
+ crypto_free_shash(tfm);
+ if (rc)
+ pr_err("crypto_shash_tfm_digest failed: %d\n", rc);
+ return rc;
+}
+
+static int sample_report_extend_mr(const struct tsm_measurements *tm,
+ const struct tsm_measurement_register *mr,
+ const u8 *data)
+{
+ SHASH_DESC_ON_STACK(desc, 0);
+ int rc;
+
+ pr_debug("%s(%s) is called\n", __func__, mr->mr_name);
+
+ desc->tfm = crypto_alloc_shash(hash_algo_name[mr->mr_hash], 0, 0);
+ if (IS_ERR(desc->tfm)) {
+ pr_err("crypto_alloc_shash failed: %ld\n", PTR_ERR(desc->tfm));
+ return PTR_ERR(desc->tfm);
+ }
+
+ rc = crypto_shash_init(desc);
+ if (!rc)
+ rc = crypto_shash_update(desc, mr->mr_value, mr->mr_size);
+ if (!rc)
+ rc = crypto_shash_finup(desc, data, mr->mr_size, mr->mr_value);
+ crypto_free_shash(desc->tfm);
+ if (rc)
+ pr_err("SHA calculation failed: %d\n", rc);
+ return rc;
+}
+
+#define MR_(mr, hash) .mr_value = &sample_report.mr, TSM_MR_(mr, hash)
+static const struct tsm_measurement_register sample_mrs[] = {
+ /* static MR, read-only */
+ { MR_(static_mr, SHA384) },
+ /* config MR, read-only */
+ { MR_(config_mr, SHA512) | TSM_MR_F_NOHASH },
+ /* RTMR, direct extension prohibited */
+ { MR_(rtmr0, SHA256) | TSM_MR_F_LIVE },
+ /* RTMR, direct extension allowed */
+ { MR_(rtmr1, SHA384) | TSM_MR_F_RTMR },
+ /* RTMR, crypto agile, alaised to rtmr0 and rtmr1, respectively */
+ { .mr_value = &sample_report.rtmr0,
+ TSM_MR_(rtmr_crypto_agile, SHA256) | TSM_MR_F_RTMR },
+ { .mr_value = &sample_report.rtmr1,
+ TSM_MR_(rtmr_crypto_agile, SHA384) | TSM_MR_F_RTMR },
+ /* sha512 digest of the whole structure */
+ { MR_(report_digest, SHA512) | TSM_MR_F_LIVE },
+};
+#undef MR_
+
+static struct tsm_measurements sample_tm = {
+ .mrs = sample_mrs,
+ .nr_mrs = ARRAY_SIZE(sample_mrs),
+ .refresh = sample_report_refresh,
+ .write = sample_report_extend_mr,
+};
+
+static const struct attribute_group *sample_groups[] = {
+ NULL,
+ NULL,
+};
+
+static struct miscdevice sample_misc_dev = {
+ .name = KBUILD_MODNAME,
+ .minor = MISC_DYNAMIC_MINOR,
+ .groups = sample_groups,
+};
+
+static int __init tsm_mr_sample_init(void)
+{
+ int rc;
+
+ sample_groups[0] = tsm_mr_create_attribute_group(&sample_tm);
+ if (IS_ERR(sample_groups[0]))
+ return PTR_ERR(sample_groups[0]);
+
+ rc = misc_register(&sample_misc_dev);
+ if (rc)
+ tsm_mr_free_attribute_group(sample_groups[0]);
+ return rc;
+}
+
+static void __exit tsm_mr_sample_exit(void)
+{
+ misc_deregister(&sample_misc_dev);
+ tsm_mr_free_attribute_group(sample_groups[0]);
+}
+
+module_init(tsm_mr_sample_init);
+module_exit(tsm_mr_sample_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Sample module using tsm-mr to expose emulated MRs");

--
2.43.0