Re: [PATCH v2 3/4] KEYS: Added BUILTIN_TRUSTED_KEYS enum to measure keys added to builtin_trusted_keys keyring

[Lakshmi Ramasubramanian]

On 10/27/19 7:33 AM, Mimi Zohar wrote:

> .builtin_trusted_keys is a trusted keyring, which is created by the
> kernel. ÂIt cannot be deleted or replaced by userspace, so it should
> be possible to correlate a keyring name with a keyring number on
> policy load.

Yes - at policy load we can map a keyring name to a keyring number.

But at runtime we still need to know if the keyring parameter passed to 
the IMA hook function is configured to be measured.

void ima_post_key_create_or_update(struct key *keyring, struct key *key,
				   unsigned long flags, bool create);
{
   => Get the keyring number for the given "keyring".
   => Check if the keyring number is in the configured IMA policy.
   => If yes, measure the key.
   => Else, do nothing.
}

Did I misunderstand what you had stated?

> > diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> > index fc376a323908..25566c74e679 100644
> > --- a/Documentation/ABI/testing/ima_policy
> > +++ b/Documentation/ABI/testing/ima_policy
> > @@ -29,6 +29,7 @@ Description:
> >   				[FIRMWARE_CHECK]
> >   				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> >   				[KEXEC_CMDLINE]
> > +				[BUILTIN_TRUSTED_KEYS]
>
> The .builtin_trusted_keys is the name of a keyring, not of an IMA
> hook. ÂDefine a new IMA policy "keyring=" option, where keyring is
> optional. ÂSome IMA policy rules might look like:
>
> # measure all keys
> measure func=KEYRING_CHECK
>
> # measure keys on the IMA keyring
> measure func=KEYRING_CHECK keyring=".ima"
>
> # measure keys on the BUILTIN and IMA keyrings into a different PCR
> measure func=KEYRING_CHECK keyring=".builtin_trusted_keys|.ima" pcr=11

I agree - I'll take a look at this.

> "func", in this case, should be something like "KEYRING_CHECK". ÂNo
> mapping is necessary.
Agree.

> >   	if (!ima_initialized) {
> > -		ima_queue_key_for_measurement(key, NONE);
> > +		ima_queue_key_for_measurement(key, func);
> >   		return;
> >   	}
> >   
> >   	pk = key->payload.data[asym_crypto];
> >   	process_buffer_measurement(pk->key, pk->keylen,
> >   				   key->description,
> > -				   NONE, 0);
> > +				   func, 0);
>
> Pass the "keyring" to process_buffer_measurement() and on to
> ima_get_action(), so that ima_get_action() determines whether the
> keyring is in policy.

Agree.

thanks,
 -lakshmi