[PATCH RFC v3 2/2] tsm: Add TVM Measurement Sample Code

From: Cedric Xing
Date: Tue Dec 10 2024 - 22:22:38 EST

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
│ └── 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, `rtmr0/sha256/digest` is read-only.
- `rtmr1` is an RTMR with `TSM_MR_F_W` **set**, permitting direct
extensions; thus, `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 can be found in `samples/tsm/measurement-example.c`.

Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx>
---
MAINTAINERS | 1 +
samples/Kconfig | 4 ++
samples/Makefile | 1 +
samples/tsm/Makefile | 2 +
samples/tsm/measurement-example.c | 113 ++++++++++++++++++++++++++++++++++++++
5 files changed, 121 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 4c833fa9e388..a4074cea0f16 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -23848,6 +23848,7 @@ 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@xxxxxxx>
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..c5d6f44211dc
--- /dev/null
+++ b/samples/tsm/measurement-example.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2024 Intel Corporation. All rights reserved. */
+
+#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];
+} example_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 example_report_refresh(struct tsm_measurement *tmr,
+ const struct tsm_measurement_register *mr)
+{
+ pr_debug("%s(%s,%s)\n", __func__, tmr->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 example_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)\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 = &example_report.mr, TSM_MR_(mr, hash)
+static const struct tsm_measurement_register example_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 = &example_report.rtmr0,
+ TSM_MR_(rtmr_crypto_agile, SHA256) | TSM_MR_F_RTMR | TSM_MR_F_W },
+ { .mr_value = &example_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 example_measurement_provider = {
+ .name = "measurement-example",
+ .mrs = example_mrs,
+ .refresh = example_report_refresh,
+ .extend = example_report_extend_mr,
+};
+
+static int __init measurement_example_init(void)
+{
+ int rc;
+
+ rc = tsm_register_measurement(&example_measurement_provider);
+ pr_debug("tsm_register_measurement(%p)=%d\n", &example_measurement_provider, rc);
+ return rc;
+}
+
+static void __exit measurement_example_exit(void)
+{
+ int rc;
+
+ rc = tsm_unregister_measurement(&example_measurement_provider);
+ pr_debug("tsm_unregister_measurement(%p)=%d\n", &example_measurement_provider, rc);
+}
+
+module_init(measurement_example_init);
+module_exit(measurement_example_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Sample tsm_measurement implementation");

--
2.43.0