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

Ahmad Fatoum
2021-12-13T11:37:18Z

Hello Matthias,

On 13.12.21 12:00, Matthias Schiffer wrote:
> On Mon, 2021-10-11 at 12:02 +0200, Ahmad Fatoum wrote:
>> The Cryptographic Acceleration and Assurance Module (CAAM) is an IP
>> Reviewed-by: David Gstir <david@sigma-star.at>
>> Tested-By: Tim Harvey <tharvey@gateworks.com>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>
>
> Tested-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>

Thanks for testing! Should I add your Tested-by: to the whole series,
or only this patch here?

> 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?

I don't use the vendor fork, so compatibility with it wasn't a criteria
for me. The format used in this series is very straight-forward:
Key modifier is kernel:trusted and blob is exactly what's returned by
the CAAM. What would you change to make it linux-imx compatible?

> 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.

For now, this is pointed out in the documentation. If you have a suggestion
on a specific condition we should check and issue a diagnostic on, I can
incorporate it. An exhaustive if WARN_ON(!secure()) is impossible, but
having some warning for unsuspecting users would indeed be nice.

Cheers,
Ahmad

>> ---
>> 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);
>
>

--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |