[PATCH v2 2/4] tsm: Add TSM measurement sample code

[Cedric Xing <cedric.xing@intel.com>]

This sample kernel module demonstrates how to make MRs accessible to user
mode through TSM.

Once loaded, this module registers a virtual measurement provider with the
TSM core and will result in the directory tree below.

/sys/kernel/tsm/
└── tsm_mr_sample
    ├── config_mr
    │   └── sha512
    │       └── digest
    ├── report_digest
    │   └── sha512
    │       └── digest
    ├── rtmr0
    │   └── sha256
    │       └── digest
    ├── rtmr1
    │   └── sha384
    │       └── digest
    ├── rtmr_crypto_agile
    │   ├── sha256
    │   │   └── digest
    │   └── sha384
    │       └── digest
    └── static_mr
        └── sha384
            └── digest

Among the MRs in this example:

- `static_mr` and `config_mr` are *Readonly* (static) MRs.
- `rtmr0` is an RTMR with `TSM_MR_F_W` **cleared**, preventing direct
  extensions; as a result, the attribute rtmr0/sha256/digest is read-only.
- `rtmr1` is an RTMR with `TSM_MR_F_W` **set**, permitting direct
  extensions; thus, the attribute rtmr1/sha384/digest 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_L` flag. Its value changes each time an RTMR is extended.

More details are available in samples/tsm/tsm_mr_sample.c.

Signed-off-by: Cedric Xing <cedric.xing@intel.com>
---
 MAINTAINERS                 |   1 +
 samples/Kconfig             |  13 ++++++
 samples/Makefile            |   1 +
 samples/tsm/Makefile        |   2 +
 samples/tsm/tsm_mr_sample.c | 107 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 124 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a5eef4c7234c..1d4232f5269e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24106,6 +24106,7 @@ 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 820e00b2ed68..0b4592581648 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -184,6 +184,19 @@ config SAMPLE_TIMER
 	bool "Timer sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
 
+config SAMPLE_TSM_MR
+	tristate "TSM measurement sample"
+	depends on TSM_REPORTS
+	help
+	  Build a sample module that emulates MRs (Measurement Registers) and
+	  exposes them to user mode applications through the TSM sysfs
+	  interface (/sys/kernel/tsm/tsm_mr_sample/).
+
+	  The module name will be tsm-mr-sample when built as a module.
+
+	  Note: TSM_MR_MAXBANKS must be at least 2 for this sample to work
+	  properly.
+
 config SAMPLE_UHID
 	bool "UHID sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
diff --git a/samples/Makefile b/samples/Makefile
index f24cd0d72dd0..c4b6dcc81df6 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE)		+= fprobe/
 obj-$(CONFIG_SAMPLES_RUST)		+= rust/
 obj-$(CONFIG_SAMPLE_DAMON_WSSE)		+= damon/
 obj-$(CONFIG_SAMPLE_DAMON_PRCL)		+= damon/
+obj-$(CONFIG_SAMPLE_TSM_MR)		+= tsm/
diff --git a/samples/tsm/Makefile b/samples/tsm/Makefile
new file mode 100644
index 000000000000..587c3947b3a7
--- /dev/null
+++ b/samples/tsm/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_TSM_MR) += tsm_mr_sample.o
diff --git a/samples/tsm/tsm_mr_sample.c b/samples/tsm/tsm_mr_sample.c
new file mode 100644
index 000000000000..4c2c6cde36e1
--- /dev/null
+++ b/samples/tsm/tsm_mr_sample.c
@@ -0,0 +1,107 @@
+// 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.h>
+#include <crypto/hash_info.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 user_data[SHA512_DIGEST_SIZE];
+	u8 report_digest[SHA512_DIGEST_SIZE];
+} sample_report = {
+	.static_mr = "static_mr",
+	.config_mr = "config_mr",
+	.rtmr0 = "rtmr0",
+	.rtmr1 = "rtmr1",
+	.user_data = "user_data",
+};
+
+DEFINE_FREE(shash, struct crypto_shash *, if (!IS_ERR(_T)) crypto_free_shash(_T));
+
+static int sample_report_refresh(struct tsm_measurement *tmr,
+				 const struct tsm_measurement_register *mr)
+{
+	pr_debug("%s(%s,%s) is called\n", __func__, tmr->name, mr ? mr->mr_name : "<nil>");
+	struct crypto_shash *tfm __free(shash) =
+		crypto_alloc_shash(hash_algo_name[HASH_ALGO_SHA512], 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+	return crypto_shash_tfm_digest(tfm, (u8 *)&sample_report,
+				       offsetof(typeof(sample_report), report_digest),
+				       sample_report.report_digest);
+}
+
+static int sample_report_extend_mr(struct tsm_measurement *tmr,
+				   const struct tsm_measurement_register *mr, const u8 *data)
+{
+	SHASH_DESC_ON_STACK(desc, 0);
+	int rc;
+
+	pr_debug("%s(%s,%s) is called\n", __func__, tmr->name, mr->mr_name);
+
+	desc->tfm = crypto_alloc_shash(hash_algo_name[mr->mr_hash], 0, 0);
+	if (IS_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);
+	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) },
+	/* RTMR, direct extension prohibited */
+	{ MR_(rtmr0, SHA256) | TSM_MR_F_RTMR },
+	/* RTMR, direct extension allowed */
+	{ MR_(rtmr1, SHA384) | TSM_MR_F_RTMR | TSM_MR_F_W },
+	/* RTMR, crypto agile, alaised to rtmr0 and rtmr1, respectively */
+	{ .mr_value = &sample_report.rtmr0,
+	  TSM_MR_(rtmr_crypto_agile, SHA256) | TSM_MR_F_RTMR | TSM_MR_F_W },
+	{ .mr_value = &sample_report.rtmr1,
+	  TSM_MR_(rtmr_crypto_agile, SHA384) | TSM_MR_F_RTMR | TSM_MR_F_W },
+	/* most CC archs allow including user data in attestation */
+	{ MR_(report_digest, SHA512) | TSM_MR_F_L },
+	/* terminating NULL entry */
+	{}
+};
+#undef MR_
+
+static struct tsm_measurement sample_mr_provider = {
+	.name = KBUILD_MODNAME,
+	.mrs = sample_mrs,
+	.refresh = sample_report_refresh,
+	.extend = sample_report_extend_mr,
+};
+
+static int __init tsm_mr_sample_init(void)
+{
+	return tsm_register_measurement(&sample_mr_provider);
+}
+
+static void __exit tsm_mr_sample_exit(void)
+{
+	tsm_unregister_measurement(&sample_mr_provider);
+}
+
+module_init(tsm_mr_sample_init);
+module_exit(tsm_mr_sample_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Sample tsm_measurement implementation");

-- 
2.43.0