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Message-Id: <20240907-tsm-rtmr-v1-3-12fc4d43d4e7@intel.com>
Date: Sat, 07 Sep 2024 23:56:21 -0500
From: Cedric Xing <cedric.xing@...el.com>
To: Dan Williams <dan.j.williams@...el.com>,
Samuel Ortiz <sameo@...osinc.com>,
James Bottomley <James.Bottomley@...senPartnership.com>,
Lukas Wunner <lukas@...ner.de>,
Dionna Amalie Glaze <dionnaglaze@...gle.com>,
Qinkun Bao <qinkun@...gle.com>, Mikko Ylinen <mikko.ylinen@...ux.intel.com>,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: [PATCH RFC 3/3] tsm: Add TVM Measurement Sample Code
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@...el.com>
---
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
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