Subject: Re: [PATCH v5] ima: move APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime

From: Bruno Meneguele <[email-masked]>
Date: Fri, 10 Jul 2020 15:34:20 -0300

On Fri, Jul 10, 2020 at 03:03:38PM -0300, Bruno Meneguele wrote:
> On Fri, Jul 10, 2020 at 01:23:24PM -0400, Mimi Zohar wrote:
> > On Thu, 2020-07-09 at 13:46 -0300, Bruno Meneguele wrote:
> > > APPRAISE_BOOTPARAM has been marked as dependent on !ARCH_POLICY in compile
> > > time, enforcing the appraisal whenever the kernel had the arch policy option
> > > enabled.
> > 
> > > However it breaks systems where the option is set but the system didn't
> > > boot in a "secure boot" platform. In this scenario, anytime an appraisal
> > > policy (i.e. ima_policy=appraisal_tcb) is used it will be forced, without
> > > giving the user the opportunity to label the filesystem, before enforcing
> > > integrity.
> > > 
> > > Considering the ARCH_POLICY is only effective when secure boot is actually
> > > enabled this patch remove the compile time dependency and move it to a
> > > runtime decision, based on the secure boot state of that platform.
> > 
> > Perhaps we could simplify this patch description a bit?
> > 
> > The IMA_APPRAISE_BOOTPARAM config allows enabling different
> > "ima_appraise=" modes - log, fix, enforce - at run time, but not when
> > IMA architecture specific policies are enabled.  This prevents
> > properly labeling the filesystem on systems where secure boot is
> > supported, but not enabled on the platform.  Only when secure boot is
> > enabled, should these IMA appraise modes be disabled.
> > 
> > This patch removes the compile time dependency and makes it a runtime
> > decision, based on the secure boot state of that platform.
> > 
> 
> Sounds good to me.
> 
> > <snip>
> > 
> > > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> > > index a9649b04b9f1..884de471b38a 100644
> > > --- a/security/integrity/ima/ima_appraise.c
> > > +++ b/security/integrity/ima/ima_appraise.c
> > > @@ -19,6 +19,11 @@
> > >  static int __init default_appraise_setup(c
> > 
> > > har *str)
> > >  {
> > >  #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
> > > +	if (arch_ima_get_secureboot()) {
> > > +		pr_info("appraise boot param ignored: secure boot enabled");
> > 
> > Instead of a generic statement, is it possible to include the actual
> > option being denied?  Perhaps something like: "Secure boot enabled,
> > ignoring %s boot command line option"
> > 
> > Mimi
> > 
> 
> Yes, sure.
> 

Btw, would it make sense to first make sure we have a valid "str"
option and not something random to print?
 
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index a9649b04b9f1..1f1175531d3e 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -25,6 +25,16 @@ static int __init default_appraise_setup(char *str)
                ima_appraise = IMA_APPRAISE_LOG;
        else if (strncmp(str, "fix", 3) == 0)
                ima_appraise = IMA_APPRAISE_FIX;
+       else
+               pr_info("invalid \"%s\" appraise option");
+
+       if (arch_ima_get_secureboot()) {
+               if (!is_ima_appraise_enabled()) {
+                       pr_info("Secure boot enabled: ignoring ima_appraise=%s boot parameter option",
+                               str);
+                       ima_appraise = IMA_APPRAISE_ENFORCE;
+               }
+       }
 #endif
        return 1;
 }

The "else" there I think would make sense as well, at least to give the
user some feedback about a possible mispelling of him (as a separate
patch).

And "if(!is_ima_appraise_enabled())" would avoid to print anything about
"ignoring the option" to the user in case he explicitly set "enforce",
which we know there isn't any real effect but is allowed and shown in
kernel-parameters.txt.

> Thanks!
> 
> > > +		return 1;
> > > +	}
> > > +
> > >  	if (strncmp(str, "off", 3) == 0)
> > >  		ima_appraise = 0;
> > >  	else if (strncmp(str, "log", 3) == 0)
> > 
> 
> -- 
> bmeneg 
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-- 
bmeneg 
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