[RFC V2] IMA Log Snapshotting Design Proposal

[Paul Moore]

On Thu, Nov 16, 2023 at 5:41 PM Stefan Berger <stefanb at linux.ibm.com> wrote:
> On 11/16/23 17:07, Paul Moore wrote:
> > On Tue, Nov 14, 2023 at 1:58 PM Stefan Berger <stefanb at linux.ibm.com> wrote:
> >> On 11/14/23 13:36, Sush Shringarputale wrote:
> >>> On 11/13/2023 10:59 AM, Stefan Berger wrote:
> >>>> On 10/19/23 14:49, Tushar Sugandhi wrote:
> >>>>> =======================================================================
> >>>>> | Introduction |
> >>>>> =======================================================================
> >>>>> This document provides a detailed overview of the proposed Kernel
> >>>>> feature IMA log snapshotting.  It describes the motivation behind the
> >>>>> proposal, the problem to be solved, a detailed solution design with
> >>>>> examples, and describes the changes to be made in the clients/services
> >>>>> which are part of remote-attestation system.  This is the 2nd version
> >>>>> of the proposal.  The first version is present here[1].
> >>>>>
> >>>>> Table of Contents:
> >>>>> ------------------
> >>>>> A. Motivation and Background
> >>>>> B. Goals and Non-Goals
> >>>>>       B.1 Goals
> >>>>>       B.2 Non-Goals
> >>>>> C. Proposed Solution
> >>>>>       C.1 Solution Summary
> >>>>>       C.2 High-level Work-flow
> >>>>> D. Detailed Design
> >>>>>       D.1 Snapshot Aggregate Event
> >>>>>       D.2 Snapshot Triggering Mechanism
> >>>>>       D.3 Choosing A Persistent Storage Location For Snapshots
> >>>>>       D.4 Remote-Attestation Client/Service-side Changes
> >>>>>           D.4.a Client-side Changes
> >>>>>           D.4.b Service-side Changes
> >>>>> E. Example Walk-through
> >>>>> F. Other Design Considerations
> >>>>> G. References
> >>>>>
> >>>>
> >>>> Userspace applications will have to know
> >>>> a) where are the shard files?
> >>> We describe the file storage location choices in section D.3, but user
> >>> applications will have to query the well-known location described there.
> >>>> b) how do I read the shard files while locking out the producer of the
> >>>> shard files?
> >>>>
> >>>> IMO, this will require a well known config file and a locking method
> >>>> (flock) so that user space applications can work together in this new
> >>>> environment. The lock could be defined in the config file or just be
> >>>> the config file itself.
> >>> The flock is a good idea for co-ordination between UM clients. While
> >>> the Kernel cannot enforce any access in this way, any UM process that
> >>> is planning on triggering the snapshot mechanism should follow that
> >>> protocol.  We will ensure we document that as the best-practices in
> >>> the patch series.
> >>
> >> It's more than 'best practices'. You need a well-known config file with
> >> well-known config options in it.
> >>
> >> All clients that were previously just trying to read new bytes from the
> >> IMA log cannot do this anymore in the presence of a log shard producer
> >> but have to also learn that a new log shard has been produced so they
> >> need to figure out the new position in the log where to read from. So
> >> maybe a counter in a config file should indicate to the log readers that
> >> a new log has been produced -- otherwise they would have to monitor all
> >> the log shard files or the log shard file's size.
> >
> > If a counter is needed, I would suggest placing it somewhere other
> > than the config file so that we can enforce limited write access to
> > the config file.
> >
> > Regardless, I imagine there are a few ways one could synchronize
> > various userspace applications such that they see a consistent view of
> > the decomposed log state, and the good news is that the approach
> > described here is opt-in from a userspace perspective.  If the
>
> A FUSE filesystem that stitches together the log shards from one or
> multiple files + IMA log file(s) could make this approach transparent
> for as long as log shards are not thrown away. Presumably it (or root)
> could bind-mount its files over the two IMA log files.
>
> > userspace does not fully support IMA log snapshotting then it never
> > needs to trigger it and the system behaves as it does today; on the
>
> I don't think individual applications should trigger it , instead some
> dedicated background process running on a machine would do that every n
> log entries or so and possibly offer the FUSE filesystem at the same
> time. In either case, once any application triggers it, all either have
> to know how to deal with the shards or FUSE would make it completely
> transparent.

Yes, performing a snapshot is a privileged operation which I expect
would be done and managed by a dedicated daemon running on the system.

-- 
paul-moore.com