[PATCH v4 5/5] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys
Matthias Schiffer
matthias.schiffer at ew.tq-group.com
Mon Dec 13 11:00:19 UTC 2021
On Mon, 2021-10-11 at 12:02 +0200, Ahmad Fatoum wrote:
> 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 at sigma-star.at>
> Tested-By: Tim Harvey <tharvey at gateworks.com>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
Tested-by: Matthias Schiffer <matthias.schiffer at ew.tq-group.com>
It is unfortunate that this implementation is incompatible with the
"secure keys" feature found in linux-imx, as that would allow upgrading
from linux-imx to mainline kernels in the future without losing access
to keys. I did not follow the discussion of previous versions of this
patch series, but I assume there is some reason why this code is not
aligned with the linux-imx implementation?
Should the kernel emit some kind of warning if CAAM-based trusted keys
are used, but the SoC has not been "closed" (if there is a nice way to
detect that)? As the CAAM is using a common example key instead of the
fused master key when HAB/secure boot are disabled, the kernel would
basically be lying about the keys being trusted in this case.
> ---
> To: Jonathan Corbet <corbet at lwn.net>
> To: David Howells <dhowells at redhat.com>
> To: Jarkko Sakkinen <jarkko at kernel.org>
> To: James Bottomley <jejb at linux.ibm.com>
> To: Mimi Zohar <zohar at linux.ibm.com>
> Cc: James Morris <jmorris at namei.org>
> Cc: "Serge E. Hallyn" <serge at hallyn.com>
> Cc: "Horia Geantă" <horia.geanta at nxp.com>
> Cc: Aymen Sghaier <aymen.sghaier at nxp.com>
> Cc: Herbert Xu <herbert at gondor.apana.org.au>
> Cc: "David S. Miller" <davem at davemloft.net>
> Cc: Udit Agarwal <udit.agarwal at nxp.com>
> Cc: Eric Biggers <ebiggers at kernel.org>
> Cc: Jan Luebbe <j.luebbe at pengutronix.de>
> Cc: David Gstir <david at sigma-star.at>
> Cc: Richard Weinberger <richard at nod.at>
> Cc: Franck LENORMAND <franck.lenormand at nxp.com>
> Cc: Sumit Garg <sumit.garg at linaro.org>
> Cc: keyrings at vger.kernel.org
> Cc: linux-crypto at vger.kernel.org
> Cc: linux-doc at vger.kernel.org
> Cc: linux-integrity at vger.kernel.org
> Cc: linux-kernel at vger.kernel.org
> Cc: linux-security-module at 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 at pengutronix.de>
> +R: Pengutronix Kernel Team <kernel at pengutronix.de>
> +L: linux-integrity at vger.kernel.org
> +L: keyrings at 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 at redhat.com>
> M: Jarkko Sakkinen <jarkko at 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 at 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 at 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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