[RFC PATCH v9 03/16] ipe: add evaluation loop and introduce 'boot_verified' as a trust provider

[Paul Moore]

On Fri, Feb 10, 2023 at 6:21 PM Fan Wu <wufan at linux.microsoft.com> wrote:
> On Tue, Jan 31, 2023 at 04:49:44PM +0100, Roberto Sassu wrote:
> > On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> > > From: Deven Bowers <deven.desai at linux.microsoft.com>
> > >
> > > IPE must have a centralized function to evaluate incoming callers
> > > against IPE's policy. This iteration of the policy against the rules
> > > for that specific caller is known as the evaluation loop.
> >
> > Not sure if you check the properties at every access.
> >
> > >From my previous comments (also for previous versions of the patches)
> > you could evaluate the property once, by calling the respective
> > functions in the other subsystems.
> >
> > Then, you reserve space in the security blob for inodes and superblocks
> > to cache the decision. The format could be a policy sequence number, to
> > ensure that the cache is valid only for the current policy, and a bit
> > for every hook you enforce.
>
> Thanks for raising this idea. I agree that if the property evaluation
> leads to a performance issue, it will be better to cache the evaluation
> result. But for this version, all the property evaluations are simple,
> so it is just as fast as accessing a cache. Also, for the initial
> version we prefer to keep the patch as minimal as possible.

FWIW, I think that is the right decision.  Keeping the initial
submission relatively small and focused has a lot of advantages when
it comes both to review and prematurely optimizing things that might
not need optimization.

-- 
paul-moore.com