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

Matthias Schiffer
2021-12-13T13:41:04Z

On Mon, 2021-12-13 at 12:36 +0100, Ahmad Fatoum wrote:
> 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?

I didn't really do any tests regarding the RNG, so I think adding it to
patches 4 and 5 would be appropriate.

>
> > 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?

It seems that the only difference is the key modifier: linux-imx uses
"SECURE_KEY". If I apply the following patch, I can load a key that was
exported on linux-imx:

--- a/security/keys/trusted-keys/trusted_caam.c
+++ b/security/keys/trusted-keys/trusted_caam.c
@@ -11,7 +11,7 @@

static struct caam_blob_priv *blobifier;

-#define KEYMOD "kernel:trusted"
+#define KEYMOD "SECURE_KEY"

static_assert(MAX_KEY_SIZE + CAAM_BLOB_OVERHEAD <= CAAM_BLOB_MAX_LEN);
static_assert(MAX_BLOB_SIZE <= CAAM_BLOB_MAX_LEN);
---

>
> > 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.

I don't know of any condition that doesn't involve looking at SoC-
specific OTP registers - that's what U-Boot does to determine whether
HAB is enabled...

Regards,
Matthias

>
> 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);
>
>