Re: [PATCH v5 6/7] IMA: add critical_data to the built-in policy rules

[Lakshmi Ramasubramanian]

On 11/6/20 7:24 AM, Mimi Zohar wrote:

Hi Mimi,

Thanks for reviewing the patches.

> Hi Lakshmi, Tushar,
>
> This patch defines a new critical_data builtin policy.  Please update
> the Subject line.
>
> On Sun, 2020-11-01 at 14:26 -0800, Tushar Sugandhi wrote:
> > From: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> >
> > The IMA hook to measure kernel critical data, namely
> > ima_measure_critical_data(), could be called before a custom IMA policy
> > is loaded. For example, SELinux calls ima_measure_critical_data() to
> > measure its state and policy when they are initialized. This occurs
> > before a custom IMA policy is loaded, and hence IMA hook will not
> > measure the data. A built-in policy is therefore needed to measure
> > critical data provided by callers before a custom IMA policy is loaded.
>
> ^Define a new critical data builtin policy to allow measuring early
> kernel integrity critical data before a custom IMA policy is loaded.

I will add the above line in the patch description.

> Either remove the references to SELinux or move this patch after the
> subsequent patch which measures SELinux critical data.

I will remove the reference to SELinux.
I think it would be better to have this patch before the SELinux 
measurement patch.

> > Add CRITICAL_DATA to built-in IMA rules if the kernel command line
> > contains "ima_policy=critical_data". Set the IMA template for this rule
> > to "ima-buf" since ima_measure_critical_data() measures a buffer.
> >
> > Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
>
> > ---
> >   security/integrity/ima/ima_policy.c | 32 +++++++++++++++++++++++++++++
> >   1 file changed, 32 insertions(+)
> >
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index ec99e0bb6c6f..dc8fe969d3fe 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
>
> > @@ -875,6 +884,29 @@ void __init ima_init_policy(void)
> >   			  ARRAY_SIZE(default_appraise_rules),
> >   			  IMA_DEFAULT_POLICY);
> >   
> > +	if (ima_use_critical_data) {
> > +		template = lookup_template_desc("ima-buf");
> > +		if (!template) {
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		ret = template_desc_init_fields(template->fmt,
> > +						&(template->fields),
> > +						&(template->num_fields));
>
> The default IMA template when measuring buffer data is "ima_buf".   Is
> there a reason for allocating and initializing it here and not
> deferring it until process_buffer_measurement()?

You are right - good catch.
I will remove the above and validate.

thanks,
 -lakshmi

> > +		if (ret)
> > +			goto out;
> > +
> > +		critical_data_rules[0].template = template;
> > +		add_rules(critical_data_rules,
> > +			  ARRAY_SIZE(critical_data_rules),
> > +			  IMA_DEFAULT_POLICY);
> > +	}
> > +
> > +out:
> > +	if (ret)
> > +		pr_err("%s failed, result: %d\n", __func__, ret);
> > +
> >   	ima_update_policy_flag();
> >   }
> >