linux-kernel - Re: [PATCH v9 6/6] IMA: Read keyrings= option from the IMA policy

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Message-Id: <1574883174.4793.318.camel@linux.ibm.com>
Date:   Wed, 27 Nov 2019 14:32:54 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        matthewgarrett@...gle.com, sashal@...nel.org,
        jamorris@...ux.microsoft.com, linux-kernel@...r.kernel.org,
        keyrings@...r.kernel.org
Subject: Re: [PATCH v9 6/6] IMA: Read keyrings= option from the IMA policy

On Tue, 2019-11-26 at 17:56 -0800, Lakshmi Ramasubramanian wrote:
> Read "keyrings=" option, if specified in the IMA policy, and store in
> the list of IMA rules when the configured IMA policy is read.
> 
> This patch defines a new policy token enum namely Opt_keyrings
> and an option flag IMA_KEYRINGS for reading "keyrings=" option
> from the IMA policy.
> 
> Updated ima_parse_rule() to parse "keyrings=" option in the policy.
> Updated ima_policy_show() to display "keyrings=" option.
> 
> The following example illustrates how key measurement can be verified.

The example is really too colloquial/verbose.  Please truncate it,
leaving just a sample "key" policy rule, with directions for verifying
the template data against the digest included in the measurement list.

> 
> Sample IMA Policy entry to measure keys
> (Added in the file /etc/ima/ima-policy):

Remove the above.

Sample "key" measurement rule:

> measure func=KEY_CHECK keyrings=.ima|.evm template=ima-buf
> 
> Build the kernel with this patch set applied and reboot to that kernel.
> 
> Ensure the IMA policy is applied:
> 
> root@...mas:/home/nramas# cat /sys/kernel/security/ima/policy
> measure func=KEY_CHECK keyrings=.ima|.evm template=ima-buf
> 
> View the initial IMA measurement log:
> 
> root@...mas:/home/nramas
> # cat /sys/kernel/security/ima/ascii_runtime_measurements
> 10 67ec... ima-ng sha1:b5466c508583f0e633df83aa58fc7c5b67ccf667 boot_aggregate
> 
> Now, add a certificate (for example, x509_ima.der) to the .ima keyring
> using evmctl (IMA-EVM Utility)
> 
> root@...mas:/home/nramas# keyctl show %:.ima
> Keyring
>  547515640 ---lswrv      0     0  keyring: .ima
> 
> root@...mas:/home/nramas# evmctl import x509_ima.der 547515640
> 
> root@...mas:/home/nramas# keyctl show %:.ima
> Keyring
>  547515640 ---lswrv      0     0  keyring: .ima
>  809678766 --als--v      0     0   \_ asymmetric: hostname: whoami signing key: 052dd247dc3c36...
> 
> View the updated IMA measurement log:
> 
> root@...mas:/home/nramas#

Remove everything up to here and simply say something like:

Display "key" measurement in the IMA measurement list:

> # cat /sys/kernel/security/ima/ascii_runtime_measurements

> 10 3adf... ima-buf
> sha256:27c915b8ddb9fae7214cf0a8a7043cc3eeeaa7539bcb136f8427067b5f6c3
> b7b .ima 308202863082...4aee


> root@...mas:/home/nramas#

Remove this string from all the commands.
> 
> For this sample, SHA256 should be selected as the hash algorithm
> used by IMA.
> 
> The following command verifies if the SHA256 hash generated from
> the payload in the IMA log entry (listed above) for the .ima key
> matches the SHA256 hash in the IMA log entry. The output of this
> command should match the SHA256 hash given in the IMA log entry
> (In this case, it should be
> 27c915b8ddb9fae7214cf0a8a7043cc3eeeaa7539bcb136f8427067b5f6c3b7b)

Previously you didn't use the hash value, but ".ima" to locate the
"key" measurement in the measurement list.  In each of the commands
above, it might be clearer.

> 
> root@...mas:/home/nramas

ditto

> # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements
> | grep
> 27c915b8ddb9fae7214cf0a8a7043cc3eeeaa7539bcb136f8427067b5f6c3b7b | 

> cut -d' ' -f 6 | xxd -r -p |tee ima-cert.der | sha256sum | cut -d' '
> -f 1
> 
> The above command also creates a binary file namely ima-cert.der
> using the payload in the IMA log entry. This file should be a valid
> x509 certificate which can be verified using openssl as given below:
> 
> root@...mas:/home/nramas

ditto


> # openssl x509 -in ima-cert.der -inform DER -text
> 
> The above command should display the contents of the file ima-cert.der
> as an x509 certificate.

Either the comments should be above or below the commands, not both.

> 
> The IMA policy used here allows measurement of keys added to
> ".ima" and ".evm" keyrings only. Add a key to any other keyring and
> verify that the key is not measured.

This comment would be included, if desired, when defining the policy
rule, not here.

Mimi