| Message ID | 20210614201620.30451-4-richard@nod.at |
|---|---|
| State | New |
| Headers | show |
| Series | DCP as trusted keys backend | expand |
Hello Richard, Hello David, On 14.06.21 22:16, Richard Weinberger wrote: > From: David Gstir <david@sigma-star.at> > > 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 > > Cc: Ahmad Fatoum <a.fatoum@pengutronix.de> > Cc: David Gstir <david@sigma-star.at> > Cc: David Howells <dhowells@redhat.com> > Cc: "David S. Miller" <davem@davemloft.net> > Cc: Fabio Estevam <festevam@gmail.com> > Cc: Herbert Xu <herbert@gondor.apana.org.au> > Cc: James Bottomley <jejb@linux.ibm.com> > Cc: James Morris <jmorris@namei.org> > Cc: Jarkko Sakkinen <jarkko@kernel.org> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: keyrings@vger.kernel.org > Cc: linux-arm-kernel@lists.infradead.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 > Cc: Mimi Zohar <zohar@linux.ibm.com> > Cc: NXP Linux Team <linux-imx@nxp.com> > Cc: Pengutronix Kernel Team <kernel@pengutronix.de> > Cc: Richard Weinberger <richard@nod.at> > Cc: Sascha Hauer <s.hauer@pengutronix.de> > Cc: "Serge E. Hallyn" <serge@hallyn.com> > Cc: Shawn Guo <shawnguo@kernel.org> > Co-developed-by: Richard Weinberger <richard@nod.at> > Signed-off-by: David Gstir <david@sigma-star.at> > --- > .../security/keys/trusted-encrypted.rst | 84 ++++++++++++++++++- > 1 file changed, 83 insertions(+), 1 deletion(-) > > diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst > index 80d5a5af62a1..e8413122e4bc 100644 > --- a/Documentation/security/keys/trusted-encrypted.rst > +++ b/Documentation/security/keys/trusted-encrypted.rst > @@ -35,6 +35,11 @@ safe. > Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip > fuses and is accessible to TEE only. > > + (3) 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 accessbile to the DCP encryption engine only. s/accessbile/accessible/ . In the code you differentiate between UNIQUE and OTP. Here you use OTP to mean both. Perhaps explicitly mention this? > + > * Execution isolation > > (1) TPM > @@ -46,6 +51,12 @@ safe. > Customizable set of operations running in isolated execution > environment verified via Secure/Trusted boot process. > > + (3) 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 > @@ -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) DCP > + > + Relies on Secure/Trusted boot process (called HAB by vendor) for > + platform integrity. > + > * Interfaces and APIs > > (1) TPM > @@ -74,10 +90,14 @@ safe. > TEEs have well-documented, standardized client interface and APIs. For > more details refer to ``Documentation/staging/tee.rst``. > > + (3) 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 TPM or TEE for a given > + The strength and appropriateness of a particular TPM, TEE or DCP for a given > purpose must be assessed when using them to protect security-relevant data. > > > @@ -103,6 +123,14 @@ access control policy within the trust source. > from platform specific hardware RNG or a software based Fortuna CSPRNG > which can be seeded via multiple entropy sources. > > + * 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. > + > + > Encrypted Keys > -------------- > > @@ -188,6 +216,19 @@ 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: 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 > -------------------- > > @@ -370,3 +411,44 @@ 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 > +--------------- > + > +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 tusted key using DCP is generated, we generate a random 128-bit s/tusted/trusted/ > +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. > + * > + * @fmt_version: Format version, currently being %1 > + * @blob_key: Random AES 128 key which is used to encrypt @payload, > + * @blob_key itself is encrypted with OTP or UNIQUE device key in > + * AES-128-ECB mode by DCP. > + * @nonce: Random nonce used for @payload encryption. > + * @payload_len: Length of the plain text @payload. > + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key, > + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it. > + * > + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len + > + * AES_BLOCK_SIZE. > + */ > + struct dcp_blob_fmt { > + __u8 fmt_version; > + __u8 blob_key[AES_KEYSIZE_128]; > + __u8 nonce[AES_KEYSIZE_128]; > + __le32 payload_len; > + __u8 payload[0]; [] ? > + } __packed; > Cheers, Ahmad -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst index 80d5a5af62a1..e8413122e4bc 100644 --- a/Documentation/security/keys/trusted-encrypted.rst +++ b/Documentation/security/keys/trusted-encrypted.rst @@ -35,6 +35,11 @@ safe. Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip fuses and is accessible to TEE only. + (3) 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 accessbile to the DCP encryption engine only. + * Execution isolation (1) TPM @@ -46,6 +51,12 @@ safe. Customizable set of operations running in isolated execution environment verified via Secure/Trusted boot process. + (3) 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 @@ -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) DCP + + Relies on Secure/Trusted boot process (called HAB by vendor) for + platform integrity. + * Interfaces and APIs (1) TPM @@ -74,10 +90,14 @@ safe. TEEs have well-documented, standardized client interface and APIs. For more details refer to ``Documentation/staging/tee.rst``. + (3) 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 TPM or TEE for a given + The strength and appropriateness of a particular TPM, TEE or DCP for a given purpose must be assessed when using them to protect security-relevant data. @@ -103,6 +123,14 @@ access control policy within the trust source. from platform specific hardware RNG or a software based Fortuna CSPRNG which can be seeded via multiple entropy sources. + * 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. + + Encrypted Keys -------------- @@ -188,6 +216,19 @@ 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: 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 -------------------- @@ -370,3 +411,44 @@ 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 +--------------- + +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 tusted 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. + * + * @fmt_version: Format version, currently being %1 + * @blob_key: Random AES 128 key which is used to encrypt @payload, + * @blob_key itself is encrypted with OTP or UNIQUE device key in + * AES-128-ECB mode by DCP. + * @nonce: Random nonce used for @payload encryption. + * @payload_len: Length of the plain text @payload. + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key, + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it. + * + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len + + * AES_BLOCK_SIZE. + */ + struct dcp_blob_fmt { + __u8 fmt_version; + __u8 blob_key[AES_KEYSIZE_128]; + __u8 nonce[AES_KEYSIZE_128]; + __le32 payload_len; + __u8 payload[0]; + } __packed;