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Message-ID: <bb4356d779720b8fa9c342647132cfeec938c296.camel@linux.ibm.com>
Subject: Re: [PATCH v2] IMA: support for duplicate data measurement
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Tushar Sugandhi <tusharsu@linux.microsoft.com>
Cc:     tyhicks@linux.microsoft.com, sashal@kernel.org, jmorris@namei.org,
        nramas@linux.microsoft.com, linux-integrity@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Wed, 17 Feb 2021 15:39:19 -0500
In-Reply-To: <5236e03f-9be4-f7f3-ec6c-29f00c16dc18@linux.microsoft.com>
References: <20210217024649.23405-1-tusharsu@linux.microsoft.com>
         <ab197aa9719b4218ab497b55f0bc78a0dadc83dd.camel@linux.ibm.com>
         <5236e03f-9be4-f7f3-ec6c-29f00c16dc18@linux.microsoft.com>
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On Wed, 2021-02-17 at 10:53 -0800, Tushar Sugandhi wrote:
> Thanks for the feedback Mimi.
> Appreciate it.
> 
> On 2021-02-17 7:03 a.m., Mimi Zohar wrote:
> > Hi Tushar,
> > 
> > The Subject line could be improved.  Perhaps something like - "IMA:
> > support for duplicate measurement records"
> > 
> Will do.
> 
> > On Tue, 2021-02-16 at 18:46 -0800, Tushar Sugandhi wrote:
> >> IMA does not measure duplicate data since TPM extend is a very expensive
> >> operation.  However, in some cases, the measurement of duplicate data
> >> is necessary to accurately determine the current state of the system.
> >> Eg, SELinux state changing from 'audit', to 'enforcing', and back to
> >> 'audit' again.  In this example, currently, IMA will not measure the
> >> last state change to 'audit'.  This limits the ability of attestation
> >> services to accurately determine the current state of the measurements
> >> on the system.
> > 
> > This patch description is written from your specific usecase
> > perspective, but it impacts file and buffer data measurements as well,
> > not only critical data measurements.  In all of these situations, with
> > this patch a new measurement record is added/appended to the
> > measurement list.  Please re-write the patch description making it more
> > generic.
> > 
> > For example, I would start with something like, "IMA does not include
> > duplicate file, buffer or critical data measurement records ..."
> > 
> Agreed.
> I will generalize the description further and send the v3 for review.

It would be good to boot with the ima_policy=tcb policy with/without
your patch and account for the different number of measurements.   Are
all the differences related to duplicate measurements - original file
hash -> new file hash -> original file hash - similar to what you
described.

thanks,

Mimi