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 <[email protected]>
> Signed-off-by: Richard Weinberger <[email protected]>
> Co-developed-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Gstir <[email protected]>
> ---
> .../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 <[email protected]>
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?
BR, Jarkko
Hi Jarkko,
> -----Original Message-----
> From: Jarkko Sakkinen <[email protected]>
> Sent: Wednesday, April 3, 2024 9:18 PM
> To: David Gstir <[email protected]>; Mimi Zohar <[email protected]>;
> James Bottomley <[email protected]>; Herbert Xu
> <[email protected]>; David S. Miller <[email protected]>
> Cc: Shawn Guo <[email protected]>; Jonathan Corbet
> <[email protected]>; Sascha Hauer <[email protected]>; Pengutronix
> Kernel Team <[email protected]>; Fabio Estevam
> <[email protected]>; dl-linux-imx <[email protected]>; Ahmad Fatoum
> <[email protected]>; sigma star Kernel Team
> <[email protected]>; David Howells <[email protected]>; Li
> Yang <[email protected]>; Paul Moore <[email protected]>; James
> Morris <[email protected]>; Serge E. Hallyn <[email protected]>; Paul E.
> McKenney <[email protected]>; Randy Dunlap <[email protected]>;
> Catalin Marinas <[email protected]>; Rafael J. Wysocki
> <[email protected]>; Tejun Heo <[email protected]>; Steven Rostedt
> (Google) <[email protected]>; [email protected]; linux-
> [email protected]; [email protected];
> [email protected]; [email protected]; linux-arm-
> [email protected]; [email protected]; linux-security-
> [email protected]; Richard Weinberger <[email protected]>; David
> Oberhollenzer <[email protected]>
> 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
> this email' button
>
>
> 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 <[email protected]>
> > Signed-off-by: Richard Weinberger <[email protected]>
> > Co-developed-by: David Oberhollenzer
> > <[email protected]>
> > Signed-off-by: David Oberhollenzer <[email protected]>
> > Signed-off-by: David Gstir <[email protected]>
> > ---
> > .../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 <[email protected]>
>
> 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.
Regards,
Kshitiz
> BR, Jarkko