The system's signature chain of trust is rooted in hardware and pivots to the keys baked into the kernel. IMA maintains this signature chain of trust by requiring any key being added to the IMA trusted keyring to be signed by a key on the builtin (or secondary) keyrings. This prevents a local key, needed for signing policies or other files, from being loaded on the IMA keyring, without requiring a custom built kernel (or injecting a key and resigning the kernel image). Allow users to load their own public key stored in a specific TPM2 NV Index, requiring the absence of the Platform Create and Platform Write attributes on the NV Index, to be loaded on the IMA keyring. To test this with the TPM2-software tools with a DER-encoded imacert.der: tpm2_nvdefine -C o -s 945 0x184b520 tpm2_nvwrite -C o -i imacert.der 0x184b520 Or with the IBM TSS tools: tssnvdefinespace -ha 0x184b520 -hi o -sz 945 +at ow +at or tssnvwrite -hia o -ha 0x184b520 -if imacert.der Then after a reboot, the ima keyring should contain the certificate. Note that if this feature is enabled, users should make sure an NV Index is created with accurate attributes to prevent any other users from writing or deleting the NV Index. Without this precaution, any user who has access to the TPM would be able to write a key to the NV Index and have that key loaded on the IMA trusted keyring. A distro who wants to enable this feature, for example, should ensure that the installer defines the NV Index in all cases, and only fills it if a key was provided by the user. It is strongly adviced that any NV Index created for this purpose has at least the policy_delete and policywrite attributes set, together with a non-empty policy. Those flags make sure that the policy (which would be up to them to define) is required to be satisfied to delete or write the index. Patrick Uiterwijk (3): tpm: Add support for reading a TPM NV Index integrity: Allow specifying flags in integrity_load_cert integrity: Load keys from TPM NV onto IMA keyring drivers/char/tpm/tpm-interface.c | 30 ++++ drivers/char/tpm/tpm.h | 5 + drivers/char/tpm/tpm2-cmd.c | 163 ++++++++++++++++++ include/linux/tpm.h | 65 +++++++ security/integrity/digsig.c | 11 +- security/integrity/ima/Kconfig | 22 +++ security/integrity/ima/ima_init.c | 53 ++++++ security/integrity/integrity.h | 6 +- .../platform_certs/platform_keyring.c | 2 +- 9 files changed, 349 insertions(+), 8 deletions(-) -- 2.29.2
