Re: IMA: How to manage user space signing policy with others

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

On Mon, 2013-03-04 at 10:29 -0500, Vivek Goyal wrote:
[...]

> Hi Mimi,
> 
> If we decide to merge flags, then practically we modified the
> ima_appraise_tcb policy. ima_appraise_tcb policy expects to cache the
> results and we will not do that. And this conflict just grows if we
> are forced to add more options in future.
> 
> Also as you mentioned that in some cases flag merging is OR operation
> and in another cases it might be AND operation. And we will most likely
> end up hardcoding all this. I think slowly this is getting complicated
> and as people add more complex rules things can quickly get out of hand.
> 
> I am wondering that why are we trying to make multiple policies work
> together. Can we try to keep it simple and say that at one point of
> time only one policy can be effective. It could either be a built in
> policy or user defined one. In fact that's how things are working right now.
> User defined policy replaces built-in policy.
> 
> For the sake of backward compatibility "ima_tcb" and "ima_appraise_tcb"
> can co-exist together (like today). But ima_secureboot_policy will not
> be compatible with other policies. I understand that there might be a
> desire to use multiple policies together down the line, but I guess in
> that case policies need to specified using "policy" interface. And
> ima_secureboot will be odd man out here as it can not trust the root
> to specify policy. So practically ima_secureboot will be disabled.
> 
> We just have to provide an IMA interface so that caller can query what's
> the effective policy currently. Say, IMA_POLICY_SECUREBOOT,
> IMA_POLICY_TCB, or IMA_POLICY_USER. Caller of the bprm_check() or
> bprm_post_load() can also check for current policy in force and give
> CAP_SIGNED only if desired policy is in effect.  
> 
> This reduces our options but trying to make multiple policies co-exist
> together is just making it complicated. We can take it up again when
> somebody has a strong use case of using secureboot policy along with
> other policies. In fact a user can still define a custom policy which
> is mix of multiple policies. Just that it is not compatible with
> "secureboot" policy because for that we can't trust "root" to define
> policy.

Let me get this straight.  You're suggesting that distros/users will
need to make a Kconfig build decision of enabling secureboot, including
the secureboot built-in policy, or be allowed to enable other integrity
policies.  If RH enables secureboot, then no other integrity policy will
be permitted.  Is that what you're saying, and if so, why would I agree
to this?

thanks,

Mimi