linux-kernel - Re: [PATCH v3 2/2] ima: move APPRAISE_BOOTPARAM dependency on ARCH

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Message-ID: <20200629234744.GA2756@glitch>
Date:   Mon, 29 Jun 2020 20:47:44 -0300
From:   Bruno Meneguele <bmeneg@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        erichte@...ux.ibm.com, nayna@...ux.ibm.com
Subject: Re: [PATCH v3 2/2] ima: move APPRAISE_BOOTPARAM dependency on
 ARCH_POLICY to runtime

On Fri, Jun 26, 2020 at 04:40:23PM -0400, Mimi Zohar wrote:
> On Tue, 2020-06-23 at 17:26 -0300, Bruno Meneguele wrote:
> <snip>
> 
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index edde88dbe576..62dc11a5af01 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -232,7 +232,7 @@ config IMA_APPRAISE_REQUIRE_POLICY_SIGS
> >  
> >  config IMA_APPRAISE_BOOTPARAM
> >  	bool "ima_appraise boot parameter"
> > -	depends on IMA_APPRAISE && !IMA_ARCH_POLICY
> > +	depends on IMA_APPRAISE
> 
> Ok
> 
> >  	default y
> >  	help
> >  	  This option enables the different "ima_appraise=" modes
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index e493063a3c34..6742f86b6c60 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
> > @@ -732,12 +732,20 @@ void __init ima_init_policy(void)
> >  	 * and custom policies, prior to other appraise rules.
> >  	 * (Highest priority)
> >  	 */
> > -	arch_entries = ima_init_arch_policy();
> > -	if (!arch_entries)
> > -		pr_info("No architecture policies found\n");
> > -	else
> > -		add_rules(arch_policy_entry, arch_entries,
> > -			  IMA_DEFAULT_POLICY | IMA_CUSTOM_POLICY);
> > +	if (arch_ima_secure_or_trusted_boot()) {
> 
> Today only "measure" and "appraise" rules are included in the arch
> specific policy, but someone might decide they want to include "audit"
> rules as well.
> 

Right, but both arches (powerpc and x86) using specific arch policies
only add it in case secure and/or trusted boot are enabled. That's why I
considered enclosing the whole arch_policy loading in the secure/trusted
boot checking there. I would say that a fine-grained check for which
action the rules have can be added later, in a separate patchset.

> 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?

> > +		/* 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?

-- 
bmeneg 
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