[PATCH v4 00/14] ima: introduce IMA Digest Lists extension

[Roberto Sassu]

This patch set introduces a new IMA extension called IMA Digest Lists.

At early boot, the extension preloads in kernel memory reference digest
values, that can be compared with actual file digests when files are
accessed in the system.

The extension will open for new possibilities: PCR with predictable value,
that can be used for sealing policies associated to data or TPM keys;
appraisal based on reference digests already provided by Linux distribution
vendors in the software packages.

The first objective can be achieved because the PCR values does not depend
on which and when files are measured: the extension measures digest lists
sequentially and files whose digest is not in the digest list.

The second objective can be reached because the extension is able to
extract reference measurements from packages (with a user space tool) and
use it as a source for appraisal verification as the reference came from
the security.ima xattr. This approach will also reduce the overhead as only
one signature is verified for many files (as opposed to one signature for
each file with the current implementation).

This version of the patch set provides a clear separation between current
and new functionality. First, the new functionality must be explicitly
enabled from the kernel command line. Second, results of operations
performed by the extension can be distinguished from those obtained from
the existing code: measurement entries created by the extension have a
different PCR; mutable files appraised with the extension have a different
security.ima type.

The review of this patch set should start from patch 11 and 12, which
modify the IMA-Measure and IMA-Appraise submodules to use digest lists.
Patch 1 to 5 are prerequisites. Patch 6 to 10 adds support for digest
lists. Finally, patch 13 introduces two new policies to measure/appraise
rootfs and patch 14 adds the documentation (including a flow chart to
show how IMA has been modified).

The user space tools to configure digest lists are available at:

https://github.com/euleros/digest-list-tools/releases/tag/v0.3

The patch set applies on top of linux-integrity/next-queued-testing
(73589972b987).

It is necessary to apply also:
https://patchwork.kernel.org/cover/10957495/

To use appraisal, it is necessary to use a modified cpio and a modified
dracut:

https://github.com/euleros/cpio/tree/xattr-v1
https://github.com/euleros/dracut/tree/digest-lists

For now, please use it only in a testing environment.


Changelog

v3:
- move ima_lookup_loaded_digest() and ima_add_digest_data_entry() from
  ima_queue.c to ima_digest_list.c
- remove patch that introduces security.ima_algo
- add version number and type modifiers to the compact list header
- remove digest list metadata, all digest lists in the directory are
  accessed
- move loading of signing keys to user space
- add violation for both PCRs if they are selected
- introduce two new appraisal modes

v2:
- add support for multiple hash algorithms
- remove RPM parser from the kernel
- add support for parsing digest lists in user space

v1:
- add support for immutable/mutable files
- add support for appraisal with digest lists


Roberto Sassu (14):
  ima: read hash algorithm from security.ima even if appraisal is not
    enabled
  ima: generalize ima_read_policy()
  ima: generalize ima_write_policy() and raise uploaded data size limit
  ima: generalize policy file operations
  ima: use ima_show_htable_value to show violations and hash table data
  ima: add parser of compact digest list
  ima: restrict upload of converted digest lists
  ima: prevent usage of digest lists that are not measured/appraised
  ima: introduce new securityfs files
  ima: load parser digests and execute the parser at boot time
  ima: add support for measurement with digest lists
  ima: add support for appraisal with digest lists
  ima: introduce new policies initrd and appraise_initrd
  ima: add Documentation/security/IMA-digest-lists.txt

 .../admin-guide/kernel-parameters.txt         |  16 +-
 Documentation/security/IMA-digest-lists.txt   | 226 +++++++++++++
 include/linux/evm.h                           |   6 +
 include/linux/fs.h                            |   1 +
 security/integrity/evm/evm_main.c             |   2 +-
 security/integrity/iint.c                     |   1 +
 security/integrity/ima/Kconfig                |  25 ++
 security/integrity/ima/Makefile               |   1 +
 security/integrity/ima/ima.h                  |  32 +-
 security/integrity/ima/ima_api.c              |  43 ++-
 security/integrity/ima/ima_appraise.c         |  92 +++---
 security/integrity/ima/ima_digest_list.c      | 309 ++++++++++++++++++
 security/integrity/ima/ima_digest_list.h      |  69 ++++
 security/integrity/ima/ima_fs.c               | 224 ++++++++-----
 security/integrity/ima/ima_init.c             |   2 +-
 security/integrity/ima/ima_main.c             |  81 ++++-
 security/integrity/ima/ima_policy.c           |  29 +-
 security/integrity/integrity.h                |  22 ++
 18 files changed, 1018 insertions(+), 163 deletions(-)
 create mode 100644 Documentation/security/IMA-digest-lists.txt
 create mode 100644 security/integrity/ima/ima_digest_list.c
 create mode 100644 security/integrity/ima/ima_digest_list.h

-- 
2.17.1