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Message-Id: <20241031-tsm-rtmr-v2-2-1a6762795911@intel.com>
Date: Thu, 31 Oct 2024 11:50:41 -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 v2 2/2] 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
│ ├── digest
│ └── hash_algo
├── full_report
├── report_digest
│ ├── digest
│ └── hash_algo
├── rtmr0
│ ├── digest
│ └── hash_algo
├── rtmr1
│ ├── digest
│ └── hash_algo
├── static_mr
│ ├── digest
│ └── hash_algo
└── user_data
├── digest
└── hash_algo
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. It also demonstrates exposing measurements in a file.
- `rtmr0` is an RTMR with `TSM_MR_F_W` **cleared**, preventing direct
extensions; as a result, `rtmr0/digest` is read-only.
- `rtmr1` is an RTMR with `TSM_MR_F_W` **set**, permitting direct extensions;
thus, `rtmr1/digest` is writable.
- `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.
See comments in `samples/tsm/measurement-example.c` for more details.
Signed-off-by: Cedric Xing <cedric.xing@...el.com>
---
include/linux/tsm.h | 63 ++++++++++++++++++++
samples/Kconfig | 4 ++
samples/Makefile | 1 +
samples/tsm/Makefile | 2 +
samples/tsm/measurement-example.c | 117 ++++++++++++++++++++++++++++++++++++++
5 files changed, 187 insertions(+)
diff --git a/include/linux/tsm.h b/include/linux/tsm.h
index 11b0c525be30..291259fc85fc 100644
--- a/include/linux/tsm.h
+++ b/include/linux/tsm.h
@@ -5,6 +5,7 @@
#include <linux/sizes.h>
#include <linux/types.h>
#include <linux/uuid.h>
+#include <uapi/linux/hash_info.h>
#define TSM_INBLOB_MAX 64
#define TSM_OUTBLOB_MAX SZ_32K
@@ -109,4 +110,66 @@ struct tsm_ops {
int tsm_register(const struct tsm_ops *ops, void *priv);
int tsm_unregister(const struct tsm_ops *ops);
+
+/**
+ * struct tsm_measurement_register - describes an architectural measurement
+ * register (MR)
+ * @mr_name: name of the MR
+ * @mr_value: buffer containing the current value of the MR
+ * @mr_size: size of the MR - typically the digest size of @mr_hash
+ * @mr_flags: bitwise OR of flags defined in enum tsm_measurement_register_flag
+ * @mr_hash: optional hash identifier defined in include/uapi/linux/hash_info.h
+ */
+struct tsm_measurement_register {
+ const char *mr_name;
+ void *mr_value;
+ u32 mr_size;
+ u32 mr_flags;
+ enum hash_algo mr_hash;
+};
+
+/**
+ * enum tsm_measurement_register_flag - properties of an MR
+ * @TSM_MR_F_X: this MR supports the extension semantics on write
+ * @TSM_MR_F_W: this MR is writable
+ * @TSM_MR_F_R: this MR is readable. This should typically be set
+ * @TSM_MR_F_L: this MR is live - writes to other MRs may change this MR
+ * @TSM_MR_F_F: present this MR as a file (instead of a directory)
+ * @TSM_MR_F_LIVE: shorthand for L (live) and R (readable)
+ * @TSM_MR_F_RTMR: shorthand for LIVE and X (extensible)
+ */
+enum tsm_measurement_register_flag {
+ TSM_MR_F_X = 1,
+ TSM_MR_F_W = 2,
+ TSM_MR_F_R = 4,
+ TSM_MR_F_L = 8,
+ TSM_MR_F_F = 16,
+ TSM_MR_F_LIVE = TSM_MR_F_L | TSM_MR_F_R,
+ TSM_MR_F_RTMR = TSM_MR_F_LIVE | TSM_MR_F_X,
+};
+
+#define TSM_MR_(mr, hash) \
+ .mr_name = #mr, .mr_size = hash##_DIGEST_SIZE, \
+ .mr_hash = HASH_ALGO_##hash, .mr_flags = TSM_MR_F_R
+
+/**
+ * struct tsm_measurement - define CC specific MRs and methods for updating
+ * them
+ * @name: name of the measurement provider
+ * @mrs: array of MR definitions ending with mr_name set to %NULL
+ * @refresh: invoked to update the specified MR
+ * @extend: invoked to extend the specified MR with mr_size bytes
+ */
+struct tsm_measurement {
+ const char *name;
+ const struct tsm_measurement_register *mrs;
+ int (*refresh)(struct tsm_measurement *,
+ const struct tsm_measurement_register *);
+ int (*extend)(struct tsm_measurement *,
+ const struct tsm_measurement_register *, const u8 *);
+};
+
+int tsm_register_measurement(struct tsm_measurement *);
+int tsm_unregister_measurement(struct tsm_measurement *);
+
#endif /* __TSM_H */
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..3abd67d3e569
--- /dev/null
+++ b/samples/tsm/measurement-example.c
@@ -0,0 +1,117 @@
+// 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",
+ .rtmr0 = "rtmr0",
+ .rtmr1 = "rtmr1",
+ .user_data = "user_data",
+};
+
+DEFINE_FREE(shash, struct crypto_shash *,
+ if (!IS_ERR(_T)) crypto_free_shash(_T));
+
+static int _refresh_report(struct tsm_measurement *tmr,
+ const struct tsm_measurement_register *mr)
+{
+ pr_debug(KBUILD_MODNAME ": %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 _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(KBUILD_MODNAME ": %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);
+
+ 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, hash) .mr_value = &example_report.mr, TSM_MR_(mr, hash)
+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 | TSM_MR_F_F },
+ /* 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 },
+ /* most CC archs allow including user data in attestation */
+ { MR_(user_data, SHA512) | TSM_MR_F_W },
+ /* LIVE MR example, usually doesn't exist in real CC arch */
+ { 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 = _refresh_report,
+ .extend = _extend_mr,
+};
+
+static int __init measurement_example_init(void)
+{
+ int rc = tsm_register_measurement(&example_measurement_provider);
+ pr_debug(KBUILD_MODNAME ": tsm_register_measurement(%p)=%d\n",
+ &example_measurement_provider, rc);
+ return rc;
+}
+
+static void __exit measurement_example_exit(void)
+{
+ int rc = tsm_unregister_measurement(&example_measurement_provider);
+ pr_debug(KBUILD_MODNAME ": 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
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