Re: [PATCH v6 7/8] IMA: add a built-in policy rule for critical data measurement

[Lakshmi Ramasubramanian]

On 11/20/20 6:30 AM, Mimi Zohar wrote:

Hi Mimi,

> On Thu, 2020-11-19 at 15:26 -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.
> > Define a new critical data builtin policy to allow measuring
> > early kernel integrity critical data before a custom IMA policy is
> > loaded.
>
> Everything needing to be said seems to be included in the second
> sentence.  Does the first sentence add anything?  "Define a new
> critical data builtin policy" makes for a good Subject line.

Agreed - will update.

> > Add critical data to built-in IMA rules if the kernel command line
> > contains "ima_policy=critical_data".
>
> The boot command line parameters are defined in Documentation/admin-
> guide/kernel-parameters.txt.  Please update "ima_policy".

Will do.

> > Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   security/integrity/ima/ima_policy.c | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index c9e52dab0638..119604a3efa0 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
> > @@ -206,6 +206,10 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
> >   	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
> >   };
> >
> > +static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
> > +	{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
> > +};
> > +
> >   /* An array of architecture specific rules */
> >   static struct ima_rule_entry *arch_policy_entry __ro_after_init;
> >   
> > @@ -228,6 +232,7 @@ __setup("ima_tcb", default_measure_policy_setup);
> >   
> >   static bool ima_use_appraise_tcb __initdata;
> >   static bool ima_use_secure_boot __initdata;
> > +static bool ima_use_critical_data __ro_after_init;
>
> Unlike ima_fail_unverifiable_sigs, ima_use_critical_data is only used
> during __init.  Please change "__ro_after_init" to "__initdata".  (The
> critical data policy itself is defined properly as __ro_after_init.)

Will do.

> >   static bool ima_fail_unverifiable_sigs __ro_after_init;
> >   static int __init policy_setup(char *str)
> >   {
> > @@ -242,6 +247,8 @@ static int __init policy_setup(char *str)
> >   			ima_use_appraise_tcb = true;
> >   		else if (strcmp(p, "secure_boot") == 0)
> >   			ima_use_secure_boot = true;
> > +		else if (strcmp(p, "critical_data") == 0)
> > +			ima_use_critical_data = true;
> >   		else if (strcmp(p, "fail_securely") == 0)
> >   			ima_fail_unverifiable_sigs = true;
> >   		else
> > @@ -875,6 +882,11 @@ void __init ima_init_policy(void)
> >   			  ARRAY_SIZE(default_appraise_rules),
> >   			  IMA_DEFAULT_POLICY);
> >   
> > +	if (ima_use_critical_data)
> > +		add_rules(critical_data_rules,
> > +			  ARRAY_SIZE(critical_data_rules),
> > +			  IMA_DEFAULT_POLICY);
> > +
> >   	ima_update_policy_flag();
> >   }
> >   

thanks,
 -lakshmi