[EXT] [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new trust source
David Gstir
david at sigma-star.at
Mon Apr 29 11:35:04 UTC 2024
Hi Kshitiz,
> On 09.04.2024, at 11:48, Kshitiz Varshney <kshitiz.varshney at nxp.com> wrote:
>
> Hi Jarkko,
>
>
>> -----Original Message-----
>> From: Jarkko Sakkinen <jarkko at kernel.org>
>> Sent: Wednesday, April 3, 2024 9:18 PM
>> To: David Gstir <david at sigma-star.at>; Mimi Zohar <zohar at linux.ibm.com>;
>> James Bottomley <jejb at linux.ibm.com>; Herbert Xu
>> <herbert at gondor.apana.org.au>; David S. Miller <davem at davemloft.net>
>> Cc: Shawn Guo <shawnguo at kernel.org>; Jonathan Corbet
>> <corbet at lwn.net>; Sascha Hauer <s.hauer at pengutronix.de>; Pengutronix
>> Kernel Team <kernel at pengutronix.de>; Fabio Estevam
>> <festevam at gmail.com>; dl-linux-imx <linux-imx at nxp.com>; Ahmad Fatoum
>> <a.fatoum at pengutronix.de>; sigma star Kernel Team
>> <upstream+dcp at sigma-star.at>; David Howells <dhowells at redhat.com>; Li
>> Yang <leoyang.li at nxp.com>; Paul Moore <paul at paul-moore.com>; James
>> Morris <jmorris at namei.org>; Serge E. Hallyn <serge at hallyn.com>; Paul E.
>> McKenney <paulmck at kernel.org>; Randy Dunlap <rdunlap at infradead.org>;
>> Catalin Marinas <catalin.marinas at arm.com>; Rafael J. Wysocki
>> <rafael.j.wysocki at intel.com>; Tejun Heo <tj at kernel.org>; Steven Rostedt
>> (Google) <rostedt at goodmis.org>; linux-doc at vger.kernel.org; linux-
>> kernel at vger.kernel.org; linux-integrity at vger.kernel.org;
>> keyrings at vger.kernel.org; linux-crypto at vger.kernel.org; linux-arm-
>> kernel at lists.infradead.org; linuxppc-dev at lists.ozlabs.org; linux-security-
>> module at vger.kernel.org; Richard Weinberger <richard at nod.at>; David
>> Oberhollenzer <david.oberhollenzer at sigma-star.at>
>> Subject: [EXT] Re: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new
>> trust source
>>
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>>
>> On Wed Apr 3, 2024 at 10:21 AM EEST, David Gstir wrote:
>>> Update the documentation for trusted and encrypted KEYS with DCP as
>>> new trust source:
>>>
>>> - Describe security properties of DCP trust source
>>> - Describe key usage
>>> - Document blob format
>>>
>>> Co-developed-by: Richard Weinberger <richard at nod.at>
>>> Signed-off-by: Richard Weinberger <richard at nod.at>
>>> Co-developed-by: David Oberhollenzer
>>> <david.oberhollenzer at sigma-star.at>
>>> Signed-off-by: David Oberhollenzer <david.oberhollenzer at sigma-star.at>
>>> Signed-off-by: David Gstir <david at sigma-star.at>
>>> ---
>>> .../security/keys/trusted-encrypted.rst | 53 +++++++++++++++++++
>>> security/keys/trusted-keys/trusted_dcp.c | 19 +++++++
>>> 2 files changed, 72 insertions(+)
>>>
>>> diff --git a/Documentation/security/keys/trusted-encrypted.rst
>>> b/Documentation/security/keys/trusted-encrypted.rst
>>> index e989b9802f92..f4d7e162d5e4 100644
>>> --- a/Documentation/security/keys/trusted-encrypted.rst
>>> +++ b/Documentation/security/keys/trusted-encrypted.rst
>>> @@ -42,6 +42,14 @@ safe.
>>> randomly generated and fused into each SoC at manufacturing time.
>>> Otherwise, a common fixed test key is used instead.
>>>
>>> + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX
>>> + SoCs)
>>> +
>>> + Rooted to a one-time programmable key (OTP) that is generally
>> burnt
>>> + in the on-chip fuses and is accessible to the DCP encryption engine
>> only.
>>> + DCP provides two keys that can be used as root of trust: the OTP
>> key
>>> + and the UNIQUE key. Default is to use the UNIQUE key, but selecting
>>> + the OTP key can be done via a module parameter
>> (dcp_use_otp_key).
>>> +
>>> * Execution isolation
>>>
>>> (1) TPM
>>> @@ -57,6 +65,12 @@ safe.
>>>
>>> Fixed set of operations running in isolated execution environment.
>>>
>>> + (4) DCP
>>> +
>>> + Fixed set of cryptographic operations running in isolated execution
>>> + environment. Only basic blob key encryption is executed there.
>>> + The actual key sealing/unsealing is done on main processor/kernel
>> space.
>>> +
>>> * Optional binding to platform integrity state
>>>
>>> (1) TPM
>>> @@ -79,6 +93,11 @@ safe.
>>> Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
>>> for platform integrity.
>>>
>>> + (4) DCP
>>> +
>>> + Relies on Secure/Trusted boot process (called HAB by vendor) for
>>> + platform integrity.
>>> +
>>> * Interfaces and APIs
>>>
>>> (1) TPM
>>> @@ -94,6 +113,11 @@ safe.
>>>
>>> Interface is specific to silicon vendor.
>>>
>>> + (4) DCP
>>> +
>>> + Vendor-specific API that is implemented as part of the DCP crypto
>> driver in
>>> + ``drivers/crypto/mxs-dcp.c``.
>>> +
>>> * Threat model
>>>
>>> The strength and appropriateness of a particular trust source
>>> for a given @@ -129,6 +153,13 @@ selected trust source:
>>> CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure
>> the device
>>> is probed.
>>>
>>> + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
>>> +
>>> + The DCP hardware device itself does not provide a dedicated RNG
>> interface,
>>> + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do
>> have
>>> + a dedicated hardware RNG that is independent from DCP which can be
>> enabled
>>> + to back the kernel RNG.
>>> +
>>> Users may override this by specifying ``trusted.rng=kernel`` on the
>>> kernel command-line to override the used RNG with the kernel's random
>> number pool.
>>>
>>> @@ -231,6 +262,19 @@ Usage::
>>> CAAM-specific format. The key length for new keys is always in bytes.
>>> Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
>>>
>>> +Trusted Keys usage: DCP
>>> +-----------------------
>>> +
>>> +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 this DCP key-blob implementation. The key
>>> +length for new keys is always in bytes. Trusted Keys can be 32 - 128 bytes
>> (256 - 1024 bits).
>>> +
>>> Encrypted Keys usage
>>> --------------------
>>>
>>> @@ -426,3 +470,12 @@ string length.
>>> privkey is the binary representation of TPM2B_PUBLIC excluding the
>>> initial TPM2B header which can be reconstructed from the ASN.1 octed
>>> string length.
>>> +
>>> +DCP Blob Format
>>> +---------------
>>> +
>>> +.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
>>> + :doc: dcp blob format
>>> +
>>> +.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
>>> + :identifiers: struct dcp_blob_fmt
>>> diff --git a/security/keys/trusted-keys/trusted_dcp.c
>>> b/security/keys/trusted-keys/trusted_dcp.c
>>> index 16c44aafeab3..b5f81a05be36 100644
>>> --- a/security/keys/trusted-keys/trusted_dcp.c
>>> +++ b/security/keys/trusted-keys/trusted_dcp.c
>>> @@ -19,6 +19,25 @@
>>> #define DCP_BLOB_VERSION 1
>>> #define DCP_BLOB_AUTHLEN 16
>>>
>>> +/**
>>> + * DOC: dcp blob format
>>> + *
>>> + * The Data Co-Processor (DCP) provides hardware-bound AES keys using
>>> +its
>>> + * AES encryption engine only. It does not provide direct key
>> sealing/unsealing.
>>> + * To make DCP hardware encryption keys usable as trust source, we
>>> +define
>>> + * our own custom format that uses a hardware-bound key to secure the
>>> +sealing
>>> + * key stored in the key blob.
>>> + *
>>> + * Whenever a new trusted key using DCP is generated, we generate a
>>> +random 128-bit
>>> + * blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are
>>> +used to
>>> + * encrypt the trusted key payload using AES-128-GCM.
>>> + *
>>> + * The BEK itself is encrypted using the hardware-bound key using the
>>> +DCP's AES
>>> + * encryption engine with AES-128-ECB. The encrypted BEK, generated
>>> +nonce,
>>> + * BEK-encrypted payload and authentication tag make up the blob
>>> +format together
>>> + * with a version number, payload length and authentication tag.
>>> + */
>>> +
>>> /**
>>> * struct dcp_blob_fmt - DCP BLOB format.
>>> *
>>
>> Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>
>>
>> I can only test that this does not break a machine without the hardware
>> feature.
>>
>> Is there anyone who could possibly peer test these patches?
> I am already working on testing this patchset on i.MX6 platform.
Did you get around to testing this?
I’d greatly appreciate a Tested-by for this. :-)
Thanks!
BR, David
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