Subject: Re: [PATCH 09/24] kexec_file: Disable at runtime if securelevel has
 been set
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: David Howells <dhowells@redhat.com>
Cc: Dave Young <dyoung@redhat.com>, linux-kernel@vger.kernel.org,
        Matthew Garrett <mjg59@srcf.ucam.org>, linux-efi@vger.kernel.org,
        gnomes@lxorguk.ukuu.org.uk, Chun-Yi Lee <jlee@suse.com>,
        gregkh@linuxfoundation.org, kexec@lists.infradead.org,
        linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
        matthew.garrett@nebula.com
Date: Fri, 07 Apr 2017 08:36:17 -0400
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On Fri, 2017-04-07 at 10:17 +0100, David Howells wrote:
> Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> 
> > > Okay, fair enough.  I can stick in an OR with an IS_ENABLED on some IMA
> > > symbol.  CONFIG_IMA_KEXEC maybe?  And also require IMA be enabled?
> > 
> > Not quite, since as Dave pointed out, IMA is policy driven.  As a
> > policy is installed, we could set a flag.
> 
> Does such a flag exist as yet?

Not exactly what is needed.  There's a flag named ima_appraise, which
is used internally in IMA. A temporary flag is created, while
validating the rules.

	if (default_appraise_rules[i].func == POLICY_CHECK)
        	temp_ima_appraise |= IMA_APPRAISE_POLICY;

        if (!result && (entry->action == UNKNOWN))
                result = -EINVAL;
        else if (entry->func == MODULE_CHECK)
                temp_ima_appraise |= IMA_APPRAISE_MODULES;
        else if (entry->func == FIRMWARE_CHECK)
                temp_ima_appraise |= IMA_APPRAISE_FIRMWARE;
        else if (entry->func == POLICY_CHECK)
                temp_ima_appraise |= IMA_APPRAISE_POLICY;

If the entire policy is valid,   ima_update_policy_flag() sets the ima_appraise flag.

        ima_appraise |= temp_ima_appraise;

>From an IMA perspective, either a file hash or signature are valid,
but for this usage it must be a signature.  So in addition to testing
entry->func, above, entry->flags would need to be tested as well to
detect if IMA_DIGSIG_REQUIRED is set.

Mimi