[PATCH RFC 3/3] tsm: Add TVM Measurement Sample Code

[Cedric Xing]

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/
└── measurement-example
    ├── config_mr
    ├── full_report
    ├── report_digest
    ├── rtmr0
    │   ├── append_event
    │   ├── digest
    │   ├── event_log
    │   └── hash_algo
    ├── rtmr1
    │   ├── append_event
    │   ├── digest
    │   ├── event_log
    │   └── hash_algo
    ├── static_mr
    └── user_data

Among the MRs in this example:

- `static_mr` and `config_mr` are static MRs.
- `full_report` illustrates that a complete architecture-dependent attestation
  report structure (for instance, the `TDREPORT` structure in Intel TDX) can be
  presented as an MR.
- `user_data` represents the data provided by the software to be incorporated
  into the attestation report. Writing to this MR and then reading from
  `full_report` effectively triggers a request for an attestation report from
  the underlying CC hardware.
- `report_digest` serves as an example MR to demonstrate the use of the
  `TSM_MR_F_L` flag.
- `rtmr0` is an RTMR with `TSM_MR_F_W` **cleared**, preventing direct
  extensions; as a result, `rtmr0/digest` is read-only, and the sole method to
  extend this RTMR is by writing to `rtmr0/append_event`.
- `rtmr1` is an RTMR with `TSM_MR_F_W` **set**, permitting direct extensions;
  thus, `rtmr1/digest` is writable.

See comments in `samples/tsm/measurement-example.c` for more details.

Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx>
---
 samples/Kconfig                   |   4 ++
 samples/Makefile                  |   1 +
 samples/tsm/Makefile              |   2 +
 samples/tsm/measurement-example.c | 116 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 123 insertions(+)

diff --git a/samples/Kconfig b/samples/Kconfig
index b288d9991d27..8159d3ca6487 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -184,6 +184,10 @@ config SAMPLE_TIMER
 	bool "Timer sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
 
+config SAMPLE_TSM
+	tristate "TSM measurement sample"
+	depends on TSM_REPORTS
+
 config SAMPLE_UHID
 	bool "UHID sample"
 	depends on CC_CAN_LINK && HEADERS_INSTALL
diff --git a/samples/Makefile b/samples/Makefile
index b85fa64390c5..891f5c12cd39 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -39,3 +39,4 @@ obj-$(CONFIG_SAMPLE_KMEMLEAK)		+= kmemleak/
 obj-$(CONFIG_SAMPLE_CORESIGHT_SYSCFG)	+= coresight/
 obj-$(CONFIG_SAMPLE_FPROBE)		+= fprobe/
 obj-$(CONFIG_SAMPLES_RUST)		+= rust/
+obj-$(CONFIG_SAMPLE_TSM)		+= tsm/
diff --git a/samples/tsm/Makefile b/samples/tsm/Makefile
new file mode 100644
index 000000000000..3969a59221e9
--- /dev/null
+++ b/samples/tsm/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_TSM) += measurement-example.o
diff --git a/samples/tsm/measurement-example.c b/samples/tsm/measurement-example.c
new file mode 100644
index 000000000000..b10bda4ba1ee
--- /dev/null
+++ b/samples/tsm/measurement-example.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2024 Intel Corporation. All rights reserved. */
+
+#include <linux/module.h>
+#include <linux/tsm.h>
+#include <crypto/hash_info.h>
+#include <crypto/hash.h>
+
+struct __aligned(16)
+{
+	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];
+}
+example_report = {
+	.static_mr = "STATIC MR",
+	.config_mr = "CONFIG MR",
+};
+
+DEFINE_FREE(shash, struct crypto_shash *,
+	    if (!IS_ERR(_T)) crypto_free_shash(_T));
+
+static int _refresh_report(struct tsm_measurement_provider *pvd,
+			   const struct tsm_measurement_register *mr)
+{
+	pr_debug(KBUILD_MODNAME ": %s(%s,%s)\n", __func__, pvd->name,
+		 mr->mr_name);
+	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 *)&example_report,
+				       offsetof(typeof(example_report),
+						report_digest),
+				       example_report.report_digest);
+}
+
+static int _extend_mr(struct tsm_measurement_provider *pvd,
+		      const struct tsm_measurement_register *mr, const u8 *data)
+{
+	SHASH_DESC_ON_STACK(desc, 0);
+	int rc;
+
+	pr_debug(KBUILD_MODNAME ": %s(%s,%s)\n", __func__, pvd->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);
+
+	BUG_ON(crypto_shash_digestsize(desc->tfm) != mr->mr_size);
+
+	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) #mr, &example_report.mr, sizeof(example_report.mr), TSM_MR_F_R
+static const struct tsm_measurement_register example_mrs[] = {
+	/* the entire report can be considered as a LIVE MR */
+	{ "full_report", &example_report, sizeof(example_report),
+	  TSM_MR_F_LIVE },
+	/* static MR, read-only */
+	{ MR_(static_mr) },
+	/* config MR, read-only */
+	{ MR_(config_mr) },
+	/* RTMR, direct extension prohibited */
+	{ MR_(rtmr0) | TSM_MR_F_RTMR, HASH_ALGO_SHA256 },
+	/* RTMR, direct extension allowed */
+	{ MR_(rtmr1) | TSM_MR_F_RTMR | TSM_MR_F_W, HASH_ALGO_SHA384 },
+	/* most CC archs allow including user data in attestation */
+	{ MR_(user_data) | TSM_MR_F_W },
+	/* LIVE MR example, usually doesn't exist in real CC arch */
+	{ MR_(report_digest) | TSM_MR_F_L },
+	/* terminating NULL entry */
+	{}
+};
+#undef MR_
+
+static struct tsm_measurement_provider example_measurement_provider = {
+	.name = "measurement-example",
+	.mrs = example_mrs,
+	.refresh = _refresh_report,
+	.extend = _extend_mr,
+};
+
+static int __init measurement_example_init(void)
+{
+	int rc = tsm_register_measurement_provider(
+		&example_measurement_provider);
+	pr_debug(KBUILD_MODNAME ": tsm_register_measurement_provider(%p)=%d\n",
+		 &example_measurement_provider, rc);
+	return rc;
+}
+
+static void __exit measurement_example_exit(void)
+{
+	int rc = tsm_unregister_measurement_provider(
+		&example_measurement_provider);
+	pr_debug(KBUILD_MODNAME
+		 ": tsm_unregister_measurement_provider(%p)=%d\n",
+		 &example_measurement_provider, rc);
+}
+
+module_init(measurement_example_init);
+module_exit(measurement_example_exit);
+
+MODULE_LICENSE("GPL");

-- 
2.43.0