[PATCH v5 3/4] LSM: Define SELinux function to measure state and policy

[Stephen Smalley]

On 7/29/20 11:47 PM, Lakshmi Ramasubramanian wrote:

> SELinux configuration and policy are some of the critical data for this
> security module that needs to be measured. This measurement can be used
> by an attestation service, for instance, to verify if the configuration
> and policies have been setup correctly and that they haven't been tampered
> with at runtime.
>
> Measure SELinux configuration, policy capabilities settings, and the
> loaded policy by calling the IMA hooks ima_measure_lsm_state() and
> ima_measure_lsm_policy() respectively.
>
> Sample measurement of SELinux state and hash of the policy:
>
> 10 e32e...5ac3 ima-buf sha256:86e8...4594 selinux-state-1595389364:287899386 696e697469616c697a65643d313b656e61626c65643d313b656e666f7263696e673d303b636865636b72657170726f743d313b6e6574776f726b5f706565725f636f6e74726f6c733d313b6f70656e5f7065726d733d313b657874656e6465645f736f636b65745f636c6173733d313b616c776179735f636865636b5f6e6574776f726b3d303b6367726f75705f7365636c6162656c3d313b6e6e705f6e6f737569645f7472616e736974696f6e3d313b67656e66735f7365636c6162656c5f73796d6c696e6b733d303
> 10 f4a7...9408 ima-ng sha256:8d1d...1834 selinux-policy-hash-1595389353:863934271
>
> To verify the measurement check the following:
>
> Execute the following command to extract the measured data
> from the IMA log for SELinux configuration (selinux-state).
>
>    grep -m 1 "selinux-state" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | cut -d' ' -f 6 | xxd -r -p
>
> The output should be the list of key-value pairs. For example,
>   initialized=1;enabled=1;enforcing=0;checkreqprot=1;network_peer_controls=1;open_perms=1;extended_socket_class=1;always_check_network=0;cgroup_seclabel=1;nnp_nosuid_transition=1;genfs_seclabel_symlinks=0;
>
> To verify the measured data with the current SELinux state:
>
>   => enabled should be set to 1 if /sys/fs/selinux folder exists,
>      0 otherwise
>
> For other entries, compare the integer value in the files
>   => /sys/fs/selinux/enforce
>   => /sys/fs/selinux/checkreqprot
> And, each of the policy capabilities files under
>   => /sys/fs/selinux/policy_capabilities
>
> For selinux-policy-hash, the hash of SELinux policy is included
> in the IMA log entry.
>
> To verify the measured data with the current SELinux policy run
> the following commands and verify the output hash values match.
>
>    sha256sum /sys/fs/selinux/policy | cut -d' ' -f 1
>
>    grep -m 1 "selinux-policy-hash" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | cut -d' ' -f 4
>
> Signed-off-by: Lakshmi Ramasubramanian <nramas at linux.microsoft.com>
> Suggested-by: Stephen Smalley <stephen.smalley.work at gmail.com>
> Reported-by: kernel test robot <lkp at intel.com> # error: implicit declaration of function 'vfree'
> Reported-by: kernel test robot <lkp at intel.com> # error: implicit declaration of function 'crypto_alloc_shash'
> Reported-by: kernel test robot <lkp at intel.com> # sparse: symbol 'security_read_selinux_policy' was not declared. Should it be static?

Possibly I'm missing something but with these patches applied on top of 
next-integrity, and the following lines added to /etc/ima/ima-policy:

measure func=LSM_STATE template=ima-buf
measure func=LSM_POLICY

I still don't get the selinux-state or selinux-policy-hash entries in 
the ascii_runtime_measurements file.  No errors during loading of the 
ima policy as far as I can see.