On 3/16/2021 7:02 PM, Ahmad Fatoum wrote: > The Cryptographic Acceleration and Assurance Module (CAAM) is an IP core > built into many newer i.MX and QorIQ SoCs by NXP. > > Its blob mechanism can AES encrypt/decrypt user data using a unique > never-disclosed device-specific key. There has been multiple > discussions on how to represent this within the kernel: > > - [RFC] crypto: caam - add red blobifier > Steffen implemented[1] a PoC sysfs driver to start a discussion on how to > best integrate the blob mechanism. > Mimi suggested that it could be used to implement trusted keys. > Trusted keys back then were a TPM-only feature. > > - security/keys/secure_key: Adds the secure key support based on CAAM. > Udit added[2] a new "secure" key type with the CAAM as backend. The key > material stays within the kernel only. > Mimi and James agreed that this needs a generic interface, not specific > to CAAM. Mimi suggested trusted keys. Jan noted that this could serve as > basis for TEE-backed keys. > > - [RFC] drivers: crypto: caam: key: Add caam_tk key type > Franck added[3] a new "caam_tk" key type based on Udit's work. The key > material stays within the kernel only, but can optionally be user-set > instead of coming from RNG. James voiced the opinion that there should > be just one user-facing generic wrap/unwrap key type with multiple > possible handlers. David suggested trusted keys. > The whole point was to use caam "black blobs", with the main advantage of keys being kept encrypted in memory after "unsealing" the blobs. (Keys in blobs are encrypted with a persistent BKEK - blob KEK, derived from fuse-based OTPMK. OTOH black keys are keys encrypted with an ephemeral, random KEK that is stored in an internal caam register. When a black blob is unsealed, the key is practically rekeyed, the random key replacing the BKEK; key is never exposed in plaintext, rekeying happens in caam).
Current implementation uses "red blobs", which means keys are left unprotected in memory after blobs are unsealed. > - Introduce TEE based Trusted Keys support > Sumit reworked[4] trusted keys to support multiple possible backends with > one chosen at boot time and added a new TEE backend along with TPM. > This now sits in Jarkko's master branch to be sent out for v5.13 > > This patch series builds on top of Sumit's rework to have the CAAM as yet > another > trusted key backend. > Shouldn't the description under TRUSTED_KEYS (in security/keys/Kconfig) be updated to reflect the availability of multiple backends? Thanks, Horia
