[v3,0/5] LSM: Measure security module state

Message

Lakshmi Ramasubramanian July 17, 2020, 10:28 p.m. UTC

Critical data structures of security modules are currently not measured.
Therefore an attestation service, for instance, would not be able to
attest whether the security modules are always operating with the policies
and configuration that the system administrator had setup. The policies
and configuration for the security modules could be tampered with by
malware by exploiting Kernel vulnerabilities or modified through some
inadvertent actions on the system. Measuring such critical data would
enable an attestation service to better assess the state of the system.

IMA subsystem measures system files, command line arguments passed to
kexec, boot aggregate, keys, etc. It can be used to measure critical
data structures of security modules as well.

This change aims to address measuring critical data structures
of security modules when they are initialized, when they are updated
at runtime, and also periodically to detect any tampering.

This change set is based off of Linux Kernel version 5.8-rc5.

The following patch needs to be applied first before applying
the patches in this patch set:

    https://patchwork.kernel.org/patch/11612989/

Change log:

  v3:
      => Loop through policy_capabilities to build the state data
         to measure instead of hardcoding to current set of
         policy capabilities.
      => Added error log messages for failure conditions.

  v2:
      => Pass selinux_state struct as parameter to the function
         that measures SELinux data.
      => Use strings from selinux_policycap_names array for SELinux
         state measurement.
      => Refactored security_read_policy() to alloc kernel or user
         virtual memory and then read the SELinux policy.

  v1:
      => Per Stephen Smalley's suggestion added selinux_state booleans
         and hash of SELinux policy in the measured data for SELinux.
      => Call IMA hook from the security module directly instead of
         redirecting through the LSM.

Lakshmi Ramasubramanian (5):
  IMA: Add LSM_STATE func to measure LSM data
  IMA: Define an IMA hook to measure LSM data
  LSM: Add security_measure_data in lsm_info struct
  LSM: Define SELinux function to measure security state
  LSM: Define workqueue for measuring security module state

 Documentation/ABI/testing/ima_policy |   6 +-
 include/linux/ima.h                  |   4 +
 include/linux/lsm_hooks.h            |   3 +
 security/integrity/ima/ima.h         |   1 +
 security/integrity/ima/ima_api.c     |   2 +-
 security/integrity/ima/ima_main.c    |  17 +++
 security/integrity/ima/ima_policy.c  |  29 ++++-
 security/security.c                  |  74 ++++++++++++-
 security/selinux/Makefile            |   2 +
 security/selinux/hooks.c             |   4 +
 security/selinux/include/security.h  |  18 ++++
 security/selinux/measure.c           | 155 +++++++++++++++++++++++++++
 security/selinux/selinuxfs.c         |   1 +
 security/selinux/ss/services.c       |  66 ++++++++++--
 14 files changed, 365 insertions(+), 17 deletions(-)
 create mode 100644 security/selinux/measure.c