linux-kernel - Re: [RFC PATCH v9 03/16] ipe: add evaluation loop and introduce 'boot

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Date:   Wed, 1 Mar 2023 21:33:19 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Fan Wu <wufan@...ux.microsoft.com>
Cc:     Roberto Sassu <roberto.sassu@...weicloud.com>, corbet@....net,
        zohar@...ux.ibm.com, jmorris@...ei.org, serge@...lyn.com,
        tytso@....edu, ebiggers@...nel.org, axboe@...nel.dk,
        agk@...hat.com, snitzer@...nel.org, eparis@...hat.com,
        linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
        dm-devel@...hat.com, linux-audit@...hat.com,
        roberto.sassu@...wei.com, linux-kernel@...r.kernel.org,
        Deven Bowers <deven.desai@...ux.microsoft.com>
Subject: Re: [RFC PATCH v9 03/16] ipe: add evaluation loop and introduce
 'boot_verified' as a trust provider

On Fri, Feb 10, 2023 at 6:21 PM Fan Wu <wufan@...ux.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@...ux.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