From: Mimi Zohar <zohar@kernel.org>
To: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
linux-integrity@vger.kernel.org
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>
Subject: Re: Measure data again even when it has not changed
Date: Thu, 30 Jul 2020 08:05:53 -0400 [thread overview]
Message-ID: <1596110753.25003.3.camel@kernel.org> (raw)
In-Reply-To: <a83fdf87-d98e-b5cd-2557-2fae88b09a13@linux.microsoft.com>
On Wed, 2020-07-29 at 20:41 -0700, Lakshmi Ramasubramanian wrote:
> On 7/29/20 8:23 PM, Mimi Zohar wrote:
>
> > On Wed, 2020-07-29 at 10:17 -0700, Lakshmi Ramasubramanian wrote:
> >> Hi Mimi,
> >>
> >> I have a query related to measuring data (by IMA subsystem) when that
> >> data has been already been measured.
> >>
> >> Consider the following sequence of events:
> >>
> >> => At time T0 IMA hook is called by another subsystem to measure data
> >> "foo". IMA measures it.
> >>
> >> => At time T1 data is "bar". IMA measures it.
> >>
> >> => At time T2 data is "foo" again. But IMA doesn't measure it since it
> >> is already in the measured list.
> >>
> >> But for the subsystem making the call to IMA, the state has changed and
> >> "foo" has to be measured again.
> >>
> >> One way to address the above is to use unique "event name" in each call
> >> so that IMA measures the given data every time.
> >>
> >> Is there a better way to address the above?
> >
> > Most likely the file is being re-measured, but the new value already exists in
> > the hash table so it isn't being added to the IMA measurement list or extending
> > the TPM. When IMA was upstreamed, there was concern about TPM performance and
> > the number of measurements being extended. We've improved TPM performance quite
> > a bit. If you're not concerned about TPM performance, I would define a new
> > template data field based on i_version.
>
> In the use case I am considering the entity being measured is not a
> file, but a memory buffer - it is for measuring an LSM's data
> constructs. So i_version is not available in this case.
>
> When LSM's data changes from A to B and then back to A, hash(A) already
> exists in IMA's hash table. So A is not measured again.
>
> Since LSM state change is not expected to be frequent, TPM performance
> shouldn't be a concern.
Wouldn't a unique event name result in a new measurement every time?
Mimi
next prev parent reply other threads:[~2020-07-30 12:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-29 17:17 Measure data again even when it has not changed Lakshmi Ramasubramanian
2020-07-30 3:23 ` Mimi Zohar
2020-07-30 3:41 ` Lakshmi Ramasubramanian
2020-07-30 12:05 ` Mimi Zohar [this message]
2020-07-30 13:12 ` Lakshmi Ramasubramanian
2020-07-30 14:05 ` Stephen Smalley
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