linux-kernel - Re: [PATCH v5 1/4] IMA: Add func to measure LSM state and policy

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Date:   Thu, 30 Jul 2020 09:33:03 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>
Cc:     zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
        sashal@...nel.org, jmorris@...ei.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/4] IMA: Add func to measure LSM state and policy

On 7/30/20 9:19 AM, Casey Schaufler wrote:

>>> Critical data structures of security modules need to be measured to
>>> enable an attestation service to verify if the configuration and
>>> policies for the security modules have been setup correctly and
>>> that they haven't been tampered with at runtime. A new IMA policy is
>>> required for handling this measurement.
>>>
>>> Define two new IMA policy func namely LSM_STATE and LSM_POLICY to
>>> measure the state and the policy provided by the security modules.
> 
> If, as you suggest below, this is SELinux specific,
> these should be SELINUX_STATE and SELINUX_POLICY.
> It makes me very uncomfortable when I see LSM used
> in cases where SELinux is required. The LSM is supposed
> to be an agnostic interface, so if you need to throw
> 
> 	if (IS_ENABLED(CONFIG_SECURITY_SELINUX) &&
> 
> into the IMA code you're clearly not thinking in terms
> of the LSM layer. I have no problem with seeing SELinux
> oriented and/or specific code in IMA if that's what you want.
> Just don't call it LSM.

The hook defined in IMA is not SELinux specific - it is generic enough 
to be used by any security module to measure their STATE and POLICY.

I have implemented the measurement for SELinux to illustrate the usage.

Tyler's suggestion was to allow this IMA policy only when component(s) 
that are using it are also enabled.

  -lakshmi