linux-kernel - Re: [PATCH 2/2] ima: Support appraise_type=imasig

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Date:	Thu, 14 Feb 2013 10:03:03 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ima: Support appraise_type=imasig_optional

On Wed, Feb 13, 2013 at 05:27:01PM -0500, Mimi Zohar wrote:

[..]
> > Yep, I got that. Default policy gets overruled when a new policy is
> > loaded.
> > 
> > In secureboot mode, somehow above rule needs to take effect by default.
> > One option would be that kernel can enforce above rule.
> > (I guess by adding it to both default_list as well as policy list).
> 
> The default policy is empty, but can be replaced with boot command line
> options.  The existing options are ima_tcb and/ ima_appraise_tcb.
> Please feel free to define an additional policy.

I think just defining a new command line option is not sufficient
for secureboot use case.

- One can easily remove kernel command line option without breaking
  booting and easily bypass secureboot restrictions.

- I guess this is one mandated rule by secureboot. There might still
  be a user policy which can co-exist with this rule.

So to me this is not a new policy. It is just one mandatory rule which
gets appended to any policy in secureboot mode. Think of it as mandatory
rule imposed by kernel for any policy user can define. And in secureboot
mode a user can not get rid of this rule. (Otherwise it breaks user
space signing and one can bypass secureboot and boot into unsigned
kernel).

Thanks
Vivek
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