On 8/13/20 1:07 PM, Lakshmi Ramasubramanian wrote:
Can we make the algorithm selectable via kernel parameter and/or writing to a new selinuxfs node?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 hash of the loaded policy by calling the IMA hook ima_measure_critical_data(). Sample measurement of SELinux state and hash of the policy: 10 e32e...5ac3 ima-buf sha256:86e8...4594 selinux-state-1595389364:287899386 696e697469616c697a65643d313b656e61626c65643d313b656e666f7263696e673d303b636865636b72657170726f743d313b6e6574776f726b5f706565725f636f6e74726f6c733d313b6f70656e5f7065726d733d313b657874656e6465645f736f636b65745f636c6173733d313b616c776179735f636865636b5f6e6574776f726b3d303b6367726f75705f7365636c6162656c3d313b6e6e705f6e6f737569645f7472616e736974696f6e3d313b67656e66735f7365636c6162656c5f73796d6c696e6b733d303 10 9e81...0857 ima-buf sha256:4941...68fc selinux-policy-hash-1597335667:462051628 8d1d...1834 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 6 Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx> Suggested-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx> 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? ---diff --git a/security/selinux/measure.c b/security/selinux/measure.cnew file mode 100644 index 000000000000..f21b7de4e2ae --- /dev/null +++ b/security/selinux/measure.c @@ -0,0 +1,204 @@ +static int selinux_hash_buffer(void *buf, size_t buf_len, + void **buf_hash, int *buf_hash_len) +{ + struct crypto_shash *tfm; + struct shash_desc *desc = NULL; + void *digest = NULL; + int desc_size; + int digest_size; + int ret = 0; + + tfm = crypto_alloc_shash("sha256", 0, 0); + if (IS_ERR(tfm)) + return PTR_ERR(tfm);
