linux-kernel - Re: [PATCH] integrity/ima: Provide Kconfig option for ima-modsig template

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Message-ID: <bea7095300c3daeaae65e6e6f230d1a3a500c322.camel@aisec.fraunhofer.de>
Date:   Mon, 15 Feb 2021 15:36:51 +0000
From:   Weiß, Michael 
        <michael.weiss@...ec.fraunhofer.de>
To:     "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>
CC:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] integrity/ima: Provide Kconfig option for ima-modsig
 template

Hi Mimi,

On Mon, 2021-02-15 at 08:26 -0500, Mimi Zohar wrote:
> Hi Michael,
> 
> On Mon, 2021-02-15 at 11:23 +0100, Michael Weiß wrote:
> > 'ima-modsig' was not in the list of selectable templates in Kconfig.
> > The missing Kconfig options were added to support the ima-modsig
> > template as default template.
> > 
> > Signed-off-by: Michael Weiß <michael.weiss@...ec.fraunhofer.de>
> 
> Since 'ima-modsig' is only needed for appended signatures (e.g. kexec
> kernel image on powerpc, kernel modules) a per policy rule "template="
> option was defined.  There's also the 'ima_template=' boot command line
> option.   Between these two options, I didn't see the need for making
> it a build time default option.  Do you?

The use-case I had in mind was a simple measured boot,
no user-space applications, only to measure already signed modules
which are already signed by modsig
using a single policy line:

measure func=MODULE_CHECK

I thought for this purpose, we could just compile in the default
template to be modsig but it wasn't
selectable.

I have overlooked the policy rule "template=",
In the above use-case, it also just works to set the policy:

measure func=MODULE_CHECK template=ima-modsig

So, your are right maybe that is not necessary.

Regards,
Michael
 
> 
> The patch itself looks good. 
> 
> thanks,
> 
> Mimi
> 
> > ---
> >  security/integrity/ima/Kconfig | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index 12e9250c1bec..32b9325f49bf 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -78,6 +78,8 @@ choice
> >  		bool "ima-ng (default)"
> >  	config IMA_SIG_TEMPLATE
> >  		bool "ima-sig"
> > +	config IMA_MODSIG_TEMPLATE
> > +		bool "ima-modsig"
> >  endchoice
> >  
> >  config IMA_DEFAULT_TEMPLATE
> > @@ -86,6 +88,7 @@ config IMA_DEFAULT_TEMPLATE
> >  	default "ima" if IMA_TEMPLATE
> >  	default "ima-ng" if IMA_NG_TEMPLATE
> >  	default "ima-sig" if IMA_SIG_TEMPLATE
> > +	default "ima-modsig" if IMA_MODSIG_TEMPLATE
> >  
> >  choice
> >  	prompt "Default integrity hash algorithm"
> 
>