Re: [PATCH v3 2/2] ima: move APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime

From: Bruno Meneguele <bmeneg@redhat.com>
To: Mimi Zohar <zohar@linux.ibm.com>
Cc: linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
	erichte@linux.ibm.com, nayna@linux.ibm.com
Subject: Re: [PATCH v3 2/2] ima: move APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime
Date: Tue, 30 Jun 2020 14:00:43 -0300	[thread overview]
Message-ID: <20200630170043.GE2944@glitch> (raw)
In-Reply-To: <1593514848.5085.82.camel@linux.ibm.com>

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On Tue, Jun 30, 2020 at 07:00:48AM -0400, Mimi Zohar wrote:
> On Mon, 2020-06-29 at 20:47 -0300, Bruno Meneguele wrote:
> 
> > 
> > > I'm not if the "secure_boot" flag is available prior to calling
> > > default_appraise_setup(), but if it is, you could modify the test
> > > there to also check if the system is booted in secure boot mode (eg.
> > > IS_ENABLED(CONFIG_IMA_APPRAISE_BOOTPARAM) &&
> > > !arch_ima_get_secureboot())
> > > 
> > 
> > Well pointed. I built a custom x86 kernel with some workaround to get
> > this flag status within default_appraise_setup() and as a result the
> > flag is was correctly available. 
> > 
> > Considering the nature of this flag (platform's firmware (in all
> > arches?)) can we trust that every arch supporting secure/trusted boot
> > will have it available in the __setup() call time?
> 
> Calling default_appraise_setup() could be deferred.
> 

Hmmm.. ok, I'm going to investigate it further.
Didn't really know that.

> > 
> > > > +		/* In secure and/or trusted boot the appraisal must be
> > > > +		 * enforced, regardless kernel parameters, preventing
> > > > +		 * runtime changes */
> > > 
> > > Only "appraise" rules are enforced.
> > > 
> > 
> > Hmm.. do you mean the comment wording is wrong/"could be better",
> > pointing the "appraise" action explicitly?
> 
> No, it's more than just the comment.  Like "trusted boot", IMA-
> measurement only measures files, never enforces integrity.
>  "ima_appraise" mode is only applicable to IMA-appraisal.

ah! Ok, I see it now and in fact it shouldn't be part of the check
alongside secureboot.

Well, I'm going to rethink the approach entirely then.
As you said, only deferring default_appraise_setup() may be probably
enough.

Thanks Mimi.

-- 
bmeneg 
PGP Key: http://bmeneg.com/pubkey.txt

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