Message-Id: <7783BAE9-87DA-4DD5-ADFA-15A9B55EEF39@sigma-star.at>
Date: Mon, 29 Apr 2024 13:35:04 +0200
From: David Gstir <david@...ma-star.at>
To: Kshitiz Varshney <kshitiz.varshney@....com>
Cc: Jarkko Sakkinen <jarkko@...nel.org>,
 Mimi Zohar <zohar@...ux.ibm.com>,
 James Bottomley <jejb@...ux.ibm.com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>,
 Shawn Guo <shawnguo@...nel.org>,
 Jonathan Corbet <corbet@....net>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 "kernel@...gutronix.de" <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>,
 dl-linux-imx <linux-imx@....com>,
 Ahmad Fatoum <a.fatoum@...gutronix.de>,
 sigma star Kernel Team <upstream+dcp@...ma-star.at>,
 David Howells <dhowells@...hat.com>,
 Li Yang <leoyang.li@....com>,
 Paul Moore <paul@...l-moore.com>,
 James Morris <jmorris@...ei.org>,
 "Serge E. Hallyn" <serge@...lyn.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Randy Dunlap <rdunlap@...radead.org>,
 Catalin Marinas <catalin.marinas@....com>,
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 Tejun Heo <tj@...nel.org>,
 "Steven Rostedt (Google)" <rostedt@...dmis.org>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
 "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
 "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
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 "linux-security-module@...r.kernel.org" <linux-security-module@...r.kernel.org>,
 Richard Weinberger <richard@....at>,
 David Oberhollenzer <david.oberhollenzer@...ma-star.at>,
 Varun Sethi <V.Sethi@....com>,
 Gaurav Jain <gaurav.jain@....com>,
 Pankaj Gupta <pankaj.gupta@....com>
Subject: Re: [EXT] [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new
 trust source

Hi Kshitiz,

> On 09.04.2024, at 11:48, Kshitiz Varshney <kshitiz.varshney@....com> wrote:
> 
> Hi Jarkko,
> 
> 
>> -----Original Message-----
>> From: Jarkko Sakkinen <jarkko@...nel.org>
>> Sent: Wednesday, April 3, 2024 9:18 PM
>> To: David Gstir <david@...ma-star.at>; Mimi Zohar <zohar@...ux.ibm.com>;
>> James Bottomley <jejb@...ux.ibm.com>; Herbert Xu
>> <herbert@...dor.apana.org.au>; David S. Miller <davem@...emloft.net>
>> Cc: Shawn Guo <shawnguo@...nel.org>; Jonathan Corbet
>> <corbet@....net>; Sascha Hauer <s.hauer@...gutronix.de>; Pengutronix
>> Kernel Team <kernel@...gutronix.de>; Fabio Estevam
>> <festevam@...il.com>; dl-linux-imx <linux-imx@....com>; Ahmad Fatoum
>> <a.fatoum@...gutronix.de>; sigma star Kernel Team
>> <upstream+dcp@...ma-star.at>; David Howells <dhowells@...hat.com>; Li
>> Yang <leoyang.li@....com>; Paul Moore <paul@...l-moore.com>; James
>> Morris <jmorris@...ei.org>; Serge E. Hallyn <serge@...lyn.com>; Paul E.
>> McKenney <paulmck@...nel.org>; Randy Dunlap <rdunlap@...radead.org>;
>> Catalin Marinas <catalin.marinas@....com>; Rafael J. Wysocki
>> <rafael.j.wysocki@...el.com>; Tejun Heo <tj@...nel.org>; Steven Rostedt
>> (Google) <rostedt@...dmis.org>; linux-doc@...r.kernel.org; linux-
>> kernel@...r.kernel.org; linux-integrity@...r.kernel.org;
>> keyrings@...r.kernel.org; linux-crypto@...r.kernel.org; linux-arm-
>> kernel@...ts.infradead.org; linuxppc-dev@...ts.ozlabs.org; linux-security-
>> module@...r.kernel.org; Richard Weinberger <richard@....at>; David
>> Oberhollenzer <david.oberhollenzer@...ma-star.at>
>> Subject: [EXT] Re: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new
>> trust source
>> 
>> Caution: This is an external email. Please take care when clicking links or
>> opening attachments. When in doubt, report the message using the 'Report
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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>
>>> Signed-off-by: Richard Weinberger <richard@....at>
>>> Co-developed-by: David Oberhollenzer
>>> <david.oberhollenzer@...ma-star.at>
>>> Signed-off-by: David Oberhollenzer <david.oberhollenzer@...ma-star.at>
>>> Signed-off-by: David Gstir <david@...ma-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@...nel.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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