[PATCH v4 5/5] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys

Ahmad Fatoum
2021-10-11T10:03:48Z

The Cryptographic Acceleration and Assurance Module (CAAM) is an IP core
built into many newer i.MX and QorIQ SoCs by NXP.

The CAAM does crypto acceleration, hardware number generation and
has a blob mechanism for encapsulation/decapsulation of sensitive material.

This blob mechanism depends on a device specific random 256-bit One Time
Programmable Master Key that is fused in each SoC at manufacturing
time. This key is unreadable and can only be used by the CAAM for AES
encryption/decryption of user data.

This makes it a suitable backend (source) for kernel trusted keys.

Previous commits generalized trusted keys to support multiple backends
and added an API to access the CAAM blob mechanism. Based on these,
provide the necessary glue to use the CAAM for trusted keys.

Reviewed-by: David Gstir <david@sigma-star.at>
Tested-By: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
To: Jonathan Corbet <corbet@lwn.net>
To: David Howells <dhowells@redhat.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
To: James Bottomley <jejb@linux.ibm.com>
To: Mimi Zohar <zohar@linux.ibm.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: "Horia Geantă" <horia.geanta@nxp.com>
Cc: Aymen Sghaier <aymen.sghaier@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Udit Agarwal <udit.agarwal@nxp.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jan Luebbe <j.luebbe@pengutronix.de>
Cc: David Gstir <david@sigma-star.at>
Cc: Richard Weinberger <richard@nod.at>
Cc: Franck LENORMAND <franck.lenormand@nxp.com>
Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: keyrings@vger.kernel.org
Cc: linux-crypto@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
---
Documentation/admin-guide/kernel-parameters.txt | 1 +-
Documentation/security/keys/trusted-encrypted.rst | 42 ++++++++-
MAINTAINERS | 9 ++-
include/keys/trusted_caam.h | 11 ++-
security/keys/trusted-keys/Kconfig | 11 +-
security/keys/trusted-keys/Makefile | 2 +-
security/keys/trusted-keys/trusted_caam.c | 74 ++++++++++++++++-
security/keys/trusted-keys/trusted_core.c | 6 +-
8 files changed, 152 insertions(+), 4 deletions(-)
create mode 100644 include/keys/trusted_caam.h
create mode 100644 security/keys/trusted-keys/trusted_caam.c

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d5969452f063..0ed1165e0f55 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5767,6 +5767,7 @@
sources:
- "tpm"
- "tee"
+ - "caam"
If not specified then it defaults to iterating through
the trust source list starting with TPM and assigns the
first trust source as a backend which is initialized
diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index 1d4b4b8f12f0..ad66573ca6fd 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -35,6 +35,13 @@ safe.
Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip
fuses and is accessible to TEE only.

+ (3) CAAM (Cryptographic Acceleration and Assurance Module: IP on NXP SoCs)
+
+ When High Assurance Boot (HAB) is enabled and the CAAM is in secure
+ mode, trust is rooted to the OTPMK, a never-disclosed 256-bit key
+ randomly generated and fused into each SoC at manufacturing time.
+ Otherwise, a common fixed test key is used instead.
+
* Execution isolation

(1) TPM
@@ -46,6 +53,10 @@ safe.
Customizable set of operations running in isolated execution
environment verified via Secure/Trusted boot process.

+ (3) CAAM
+
+ Fixed set of operations running in isolated execution environment.
+
* Optional binding to platform integrity state

(1) TPM
@@ -63,6 +74,11 @@ safe.
Relies on Secure/Trusted boot process for platform integrity. It can
be extended with TEE based measured boot process.

+ (3) CAAM
+
+ Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
+ for platform integrity.
+
* Interfaces and APIs

(1) TPM
@@ -74,10 +90,13 @@ safe.
TEEs have well-documented, standardized client interface and APIs. For
more details refer to ``Documentation/staging/tee.rst``.

+ (3) CAAM
+
+ Interface is specific to silicon vendor.

* Threat model

- The strength and appropriateness of a particular TPM or TEE for a given
+ The strength and appropriateness of a particular trust source for a given
purpose must be assessed when using them to protect security-relevant data.

@@ -104,8 +123,14 @@ selected trust source:
from platform specific hardware RNG or a software based Fortuna CSPRNG
which can be seeded via multiple entropy sources.

+ * CAAM: Kernel RNG
+
+ The normal kernel random number generator is used. To seed it from the
+ CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
+ can be probed.
+
Optionally, users may specify ``trusted.kernel_rng=1`` on the kernel
-command-line to override the used RNG with the kernel's random number pool.
+command-line to force use of the kernel's random number pool.

Encrypted Keys
--------------
@@ -192,6 +217,19 @@ Usage::
specific to TEE device implementation. The key length for new keys is always
in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

+Trusted Keys usage: CAAM
+------------------------
+
+Usage::
+
+ keyctl add trusted name "new keylen" ring
+ keyctl add trusted name "load hex_blob" ring
+ keyctl print keyid
+
+"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
+specific to CAAM device implementation. The key length for new keys is always
+in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
+
Encrypted Keys usage
--------------------

diff --git a/MAINTAINERS b/MAINTAINERS
index a4a0c2baaf27..2c6514759222 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10364,6 +10364,15 @@ S: Supported
F: include/keys/trusted_tee.h
F: security/keys/trusted-keys/trusted_tee.c

+KEYS-TRUSTED-CAAM
+M: Ahmad Fatoum <a.fatoum@pengutronix.de>
+R: Pengutronix Kernel Team <kernel@pengutronix.de>
+L: linux-integrity@vger.kernel.org
+L: keyrings@vger.kernel.org
+S: Supported
+F: include/keys/trusted_caam.h
+F: security/keys/trusted-keys/trusted_caam.c
+
KEYS/KEYRINGS
M: David Howells <dhowells@redhat.com>
M: Jarkko Sakkinen <jarkko@kernel.org>
diff --git a/include/keys/trusted_caam.h b/include/keys/trusted_caam.h
new file mode 100644
index 000000000000..2fba0996b0b0
--- /dev/null
+++ b/include/keys/trusted_caam.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Pengutronix, Ahmad Fatoum <kernel@pengutronix.de>
+ */
+
+#ifndef __CAAM_TRUSTED_KEY_H
+#define __CAAM_TRUSTED_KEY_H
+
+extern struct trusted_key_ops caam_trusted_key_ops;
+
+#endif
diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
index fc4abd581abb..dbfdd8536468 100644
--- a/security/keys/trusted-keys/Kconfig
+++ b/security/keys/trusted-keys/Kconfig
@@ -24,6 +24,15 @@ config TRUSTED_KEYS_TEE
Enable use of the Trusted Execution Environment (TEE) as trusted
key backend.

-if !TRUSTED_KEYS_TPM && !TRUSTED_KEYS_TEE
+config TRUSTED_KEYS_CAAM
+ bool "CAAM-based trusted keys"
+ depends on CRYPTO_DEV_FSL_CAAM_JR >= TRUSTED_KEYS
+ select CRYPTO_DEV_FSL_CAAM_BLOB_GEN
+ default y
+ help
+ Enable use of NXP's Cryptographic Accelerator and Assurance Module
+ (CAAM) as trusted key backend.
+
+if !TRUSTED_KEYS_TPM && !TRUSTED_KEYS_TEE && !TRUSTED_KEYS_CAAM
comment "No trust source selected!"
endif
diff --git a/security/keys/trusted-keys/Makefile b/security/keys/trusted-keys/Makefile
index 2e2371eae4d5..735aa0bc08ef 100644
--- a/security/keys/trusted-keys/Makefile
+++ b/security/keys/trusted-keys/Makefile
@@ -12,3 +12,5 @@ trusted-$(CONFIG_TRUSTED_KEYS_TPM) += trusted_tpm2.o
trusted-$(CONFIG_TRUSTED_KEYS_TPM) += tpm2key.asn1.o

trusted-$(CONFIG_TRUSTED_KEYS_TEE) += trusted_tee.o
+
+trusted-$(CONFIG_TRUSTED_KEYS_CAAM) += trusted_caam.o
diff --git a/security/keys/trusted-keys/trusted_caam.c b/security/keys/trusted-keys/trusted_caam.c
new file mode 100644
index 000000000000..01adfd18adda
--- /dev/null
+++ b/security/keys/trusted-keys/trusted_caam.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 Pengutronix, Ahmad Fatoum <kernel@pengutronix.de>
+ */
+
+#include <keys/trusted_caam.h>
+#include <keys/trusted-type.h>
+#include <linux/build_bug.h>
+#include <linux/key-type.h>
+#include <soc/fsl/caam-blob.h>
+
+static struct caam_blob_priv *blobifier;
+
+#define KEYMOD "kernel:trusted"
+
+static_assert(MAX_KEY_SIZE + CAAM_BLOB_OVERHEAD <= CAAM_BLOB_MAX_LEN);
+static_assert(MAX_BLOB_SIZE <= CAAM_BLOB_MAX_LEN);
+
+static int trusted_caam_seal(struct trusted_key_payload *p, char *datablob)
+{
+ int length = p->key_len + CAAM_BLOB_OVERHEAD;
+ int ret;
+
+ ret = caam_encap_blob(blobifier, KEYMOD, p->key, p->blob, length);
+ if (ret)
+ return ret;
+
+ p->blob_len = length;
+ return 0;
+}
+
+static int trusted_caam_unseal(struct trusted_key_payload *p, char *datablob)
+{
+ int length = p->blob_len;
+ int ret;
+
+ ret = caam_decap_blob(blobifier, KEYMOD, p->blob, p->key, length);
+ if (ret)
+ return ret;
+
+ p->key_len = length - CAAM_BLOB_OVERHEAD;
+ return 0;
+}
+
+static int trusted_caam_init(void)
+{
+ int ret;
+
+ blobifier = caam_blob_gen_init();
+ if (IS_ERR(blobifier)) {
+ pr_err("Job Ring Device allocation for transform failed\n");
+ return PTR_ERR(blobifier);
+ }
+
+ ret = register_key_type(&key_type_trusted);
+ if (ret)
+ caam_blob_gen_exit(blobifier);
+
+ return ret;
+}
+
+static void trusted_caam_exit(void)
+{
+ unregister_key_type(&key_type_trusted);
+ caam_blob_gen_exit(blobifier);
+}
+
+struct trusted_key_ops caam_trusted_key_ops = {
+ .migratable = 0, /* non-migratable */
+ .init = trusted_caam_init,
+ .seal = trusted_caam_seal,
+ .unseal = trusted_caam_unseal,
+ .exit = trusted_caam_exit,
+};
diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index d2b7626cde8b..305e44651180 100644
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -9,6 +9,7 @@
#include <keys/user-type.h>
#include <keys/trusted-type.h>
#include <keys/trusted_tee.h>
+#include <keys/trusted_caam.h>
#include <keys/trusted_tpm.h>
#include <linux/capability.h>
#include <linux/err.h>
@@ -29,7 +30,7 @@ MODULE_PARM_DESC(kernel_rng, "Generate key material from kernel RNG");

static char *trusted_key_source;
module_param_named(source, trusted_key_source, charp, 0);
-MODULE_PARM_DESC(source, "Select trusted keys source (tpm or tee)");
+MODULE_PARM_DESC(source, "Select trusted keys source (tpm, tee or caam)");

static const struct trusted_key_source trusted_key_sources[] = {
#if defined(CONFIG_TRUSTED_KEYS_TPM)
@@ -38,6 +39,9 @@ static const struct trusted_key_source trusted_key_sources[] = {
#if defined(CONFIG_TRUSTED_KEYS_TEE)
{ "tee", &trusted_key_tee_ops },
#endif
+#if defined(CONFIG_TRUSTED_KEYS_CAAM)
+ { "caam", &caam_trusted_key_ops },
+#endif
};

DEFINE_STATIC_CALL_NULL(trusted_key_init, *trusted_key_sources[0].ops->init);
--
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