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

Pankaj Gupta
2022-02-22T04:30:55Z

Hi Ahmad,

> -----Original Message-----
> From: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> Sent: Monday, December 13, 2021 7:11 PM
> To: Ahmad Fatoum <a.fatoum@pengutronix.de>
> Cc: kernel@pengutronix.de; David Gstir <david@sigma-star.at>;
> tharvey@gateworks.com; James Morris <jmorris@namei.org>; Serge E.
> Hallyn <serge@hallyn.com>; Horia Geanta <horia.geanta@nxp.com>; Aymen
> Sghaier <aymen.sghaier@nxp.com>; Herbert Xu
> <herbert@gondor.apana.org.au>; David S. Miller <davem@davemloft.net>;
> Udit Agarwal <udit.agarwal@nxp.com>; Eric Biggers <ebiggers@kernel.org>;
> Jan Luebbe <j.luebbe@pengutronix.de>; Richard Weinberger
> <richard@nod.at>; Franck Lenormand <franck.lenormand@nxp.com>; Sumit
> Garg <sumit.garg@linaro.org>; keyrings@vger.kernel.org; linux-
> crypto@vger.kernel.org; linux-doc@vger.kernel.org; linux-
> integrity@vger.kernel.org; linux-kernel@vger.kernel.org; linux-security-
> module@vger.kernel.org; Jonathan Corbet <corbet@lwn.net>; David
> Howells <dhowells@redhat.com>; Jarkko Sakkinen <jarkko@kernel.org>;
> James Bottomley <jejb@linux.ibm.com>; Mimi Zohar <zohar@linux.ibm.com>
> Subject: [EXT] Re: [PATCH v4 5/5] KEYS: trusted: Introduce support for NXP
> CAAM-based trusted keys
>
> Caution: EXT Email
>
> 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...
>

Check the value fetched from the SEC Status Register (SSTA) (Offset 0xFD4h, bit 8,9 => 00b - Non-Secure, 01b - Secure, 10b - Trusted, 11b - Fail), for MOO (Mode of Operation).
And the warning can be issued accordingly.

It is to be noted that this register is part of CAAM page0, which might not be accessible to Linux, for all the iMX SoC(s).

For other SoC(s), this can be added.

> 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);
> >
> >