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

From: Roberto Sassu
Date: Tue Jun 25 2019 - 08:57:52 EST

On 6/17/2019 8:56 AM, Roberto Sassu wrote:
On 6/14/2019 7:54 PM, Roberto Sassu wrote:
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:

The patch set applies on top of linux-integrity/next-queued-testing

It is necessary to apply also:

Another dependency is:

I uploaded this patch set and all the required dependencies to:

It should be easy to test. Let me know if you have questions about the

Mimi, do you have any thoughts on this version?



Managing Director: Bo PENG, Jian LI, Yanli SHI