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Miller" Cc: David Gstir , Shawn Guo , Jonathan Corbet , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , Ahmad Fatoum , sigma star Kernel Team , David Howells , Li Yang , Paul Moore , James Morris , "Serge E. Hallyn" , "Paul E. McKenney" , Randy Dunlap , Catalin Marinas , "Rafael J. Wysocki" , Tejun Heo , "Steven Rostedt (Google)" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-security-module@vger.kernel.org, Richard Weinberger , David Oberhollenzer Subject: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new trust source Date: Wed, 3 Apr 2024 09:21:22 +0200 Message-ID: <20240403072131.54935-7-david@sigma-star.at> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240403072131.54935-1-david@sigma-star.at> References: <20240403072131.54935-1-david@sigma-star.at> Precedence: bulk X-Mailing-List: linux-integrity@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 Signed-off-by: Richard Weinberger Co-developed-by: David Oberhollenzer Signed-off-by: David Oberhollenzer Signed-off-by: David Gstir Reviewed-by: Bagas Sanjaya Reviewed-by: Jarkko Sakkinen --- .../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. *