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authorDavid Gstir <david@sigma-star.at>2024-04-03 10:21:22 +0300
committerJarkko Sakkinen <jarkko@kernel.org>2024-05-09 18:29:03 +0300
commit28c5f596ae3d1790cdc96fa5fc7370f934abfb2e (patch)
treed5da5c4c38c24acd0d25bb584729439df5cfcc94 /Documentation
parentb85b253e23bc985ecb0dad329da2147fb396223c (diff)
downloadlinux-28c5f596ae3d1790cdc96fa5fc7370f934abfb2e.tar.xz
docs: trusted-encrypted: add DCP as new trust source
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@nod.at> Signed-off-by: Richard Weinberger <richard@nod.at> Co-developed-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at> Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at> Signed-off-by: David Gstir <david@sigma-star.at> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/security/keys/trusted-encrypted.rst53
1 files changed, 53 insertions, 0 deletions
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