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Subject: Re: [PATCH v4 0/6] IMA: Infrastructure for measurement of critical
 kernel data
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Tushar Sugandhi <tusharsu@linux.microsoft.com>,
        stephen.smalley.work@gmail.com, casey@schaufler-ca.com,
        agk@redhat.com, snitzer@redhat.com, gmazyland@gmail.com
Cc:     tyhicks@linux.microsoft.com, sashal@kernel.org, jmorris@namei.org,
        nramas@linux.microsoft.com, linux-integrity@vger.kernel.org,
        selinux@vger.kernel.org, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, dm-devel@redhat.com
Date:   Sat, 24 Oct 2020 23:35:53 -0400
In-Reply-To: <20200923192011.5293-1-tusharsu@linux.microsoft.com>
References: <20200923192011.5293-1-tusharsu@linux.microsoft.com>
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Hi Tushar,

On Wed, 2020-09-23 at 12:20 -0700, Tushar Sugandhi wrote:
> There are several kernel components that contain critical data which if
> accidentally or maliciously altered, can compromise the security of the
> kernel. Example of such components would include LSMs like SELinux, or
> AppArmor; or device-mapper targets like dm-crypt, dm-verity etc.

^"the integrity of the system."

This cover letter needs to be re-written from a higher perspective,
explaining what is meant by "critical data" (e.g. kernel subsystem
specific information only stored in kernel memory).

> 
> Many of these components do not use the capabilities provided by kernel
> integrity subsystem (IMA), and thus they don't use the benefits of
> extended TPM PCR quotes and ultimately the benefits of remote attestation.

True, up until recently IMA only measured files, nothing else.  Why is
this paragraph needed?  What new information is provided?

> This series bridges this gap, so that potential kernel components that
> contain data critical to the security of the kernel could take advantage
> of IMA's measuring and quoting abilities - thus ultimately enabling
> remote attestation for their specific data.

Perhaps, something more along the lines, "This patch set defines a new
IMA hook named ... to measure critical data."

> 
> System administrators may want to pick and choose which kernel
> components they would want to enable for measurements, quoting, and
> remote attestation. To enable that, a new IMA policy is introduced.

Reverse the order of this paragraph and the following one, describing
the new feature and only afterwards explaining how it may be
constrained.

> 
> And lastly, the functionality is exposed through a function
> ima_measure_critical_data(). The functionality is generic enough to
> measure the data of any kernel component at run-time. To ensure that
> only data from supported sources are measured, the kernel component
> needs to be added to a compile-time list of supported sources (an
> "allowed list of components"). IMA validates the source passed to
> ima_measure_critical_data() against this allowed list at run-time.

This patch set must include at least one example of measuring critical
data, before it can be upstreamed.  Tushar, please coordinate with
Lakshmi and Raphael.

thanks,

Mimi