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From: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
To: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Mimi Zohar <zohar@linux.ibm.com>,
	Casey Schaufler <casey@schaufler-ca.com>,
	James Morris <jmorris@namei.org>,
	linux-integrity@vger.kernel.org,
	SElinux list <selinux@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 4/5] LSM: Define SELinux function to measure security state
Date: Mon, 20 Jul 2020 10:34:06 -0700	[thread overview]
Message-ID: <bea0cb52-2e13-fb14-b66c-b57287c23c3f@linux.microsoft.com> (raw)
In-Reply-To: <CAEjxPJ7VH18bEo6+U1GWrx=tHVGr=6XtF5_ygcfQYgdtZ74J+g@mail.gmail.com>

On 7/20/20 10:06 AM, Stephen Smalley wrote:

>> The above will ensure the following sequence will be measured:
>>    #1 State A - Measured
>>    #2 Change from State A to State B - Measured
>>    #3 Change from State B back to State A - Since the measured data is
>> same as in #1, the change will be measured only if the event name is
>> different between #1 and #3
> 
> Perhaps the timestamp / sequence number should be part of the hashed
> data instead of the event name?

If the timestamp/seqno is part of the hashed data, on every call to 
measure IMA will add a new entry in the IMA log. This would fill up the 
IMA log - even when there is no change in the measured data.

To avoid that I keep the last measurement in SELinux and measure only 
when there is a change with the timestamp in the event name.

> I can see the appraiser wanting to know two things:
> 1) The current state of the system (e.g. is it enforcing, is the
> currently loaded policy the expected one?).
> 2) Has the system ever been in an unexpected state (e.g. was it
> temporarily switched to permissive or had an unexpected policy
> loaded?)

Yes - you are right.
The appraiser will have to look at the entire IMA log (and the 
corresponding TPM PCR data) to know the above.

Time t0 => State of the system measured
Time tn => State changed and the new state measured
Time tm => State changed again and the new state measured.

Say, the measurement at "Time tn" was an illegal change, the appraiser 
would know.

> 
> I applied the patch series on top of the next-integrity branch, added
> measure func=LSM_STATE to ima-policy, and booted that kernel.  I get
> the following entries in ascii_runtime_measurements, but seemingly
> missing the final field:
> 
> 10 8a09c48af4f8a817f59b495bd82971e096e2e367 ima-ng
> sha256:21c3d7b09b62b4d0b3ed15ba990f816b94808f90b76787bfae755c4b3a44cd24
> selinux-state
> 10 e610908931d70990a2855ddb33c16af2d82ce56a ima-ng
> sha256:c8898652afd5527ef4eaf8d85f5fee1d91fcccee34bc97f6e55b96746bedb318
> selinux-policy-hash
> 
> Thus, I cannot verify. What am I missing?
> 

Looks like the template used is ima-ng which doesn't include the 
measured buffer. Please set template to "ima-buf" in the policy.

For example,
measure func=LSM_STATE template=ima-buf

thanks,
  -lakshmi



  parent reply	other threads:[~2020-07-20 17:34 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 22:28 [PATCH v3 0/5] LSM: Measure security module state Lakshmi Ramasubramanian
2020-07-17 22:28 ` [PATCH v3 1/5] IMA: Add LSM_STATE func to measure LSM data Lakshmi Ramasubramanian
2020-07-17 22:28 ` [PATCH v3 2/5] IMA: Define an IMA hook " Lakshmi Ramasubramanian
2020-07-17 22:28 ` [PATCH v3 3/5] LSM: Add security_measure_data in lsm_info struct Lakshmi Ramasubramanian
2020-07-17 22:28 ` [PATCH v3 4/5] LSM: Define SELinux function to measure security state Lakshmi Ramasubramanian
2020-07-18  3:14   ` kernel test robot
2020-07-20  2:04     ` Lakshmi Ramasubramanian
2020-07-18  3:38   ` kernel test robot
2020-07-18 15:31   ` kernel test robot
2020-07-18 15:31   ` [RFC PATCH] LSM: security_read_selinux_policy() can be static kernel test robot
2020-07-20 14:31   ` [PATCH v3 4/5] LSM: Define SELinux function to measure security state Stephen Smalley
2020-07-20 15:17     ` Lakshmi Ramasubramanian
2020-07-20 17:06       ` Stephen Smalley
2020-07-20 17:26         ` Mimi Zohar
2020-07-20 17:34         ` Lakshmi Ramasubramanian [this message]
2020-07-20 17:40           ` Stephen Smalley
2020-07-20 17:49             ` Stephen Smalley
2020-07-20 18:27               ` Lakshmi Ramasubramanian
2020-07-20 18:44                 ` Stephen Smalley
2020-07-20 18:59                   ` Lakshmi Ramasubramanian
2020-07-17 22:28 ` [PATCH v3 5/5] LSM: Define workqueue for measuring security module state Lakshmi Ramasubramanian

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