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

From: Stephen Smalley
Date: Mon Aug 03 2020 - 11:11:33 EST

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,

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@xxxxxxxxxxxxxxxxxxx>
Suggested-by: Stephen Smalley <>
Reported-by: kernel test robot <lkp@xxxxxxxxx> # error: implicit declaration of function 'vfree'
Reported-by: kernel test robot <lkp@xxxxxxxxx> # error: implicit declaration of function 'crypto_alloc_shash'
Reported-by: kernel test robot <lkp@xxxxxxxxx> # 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.