Re: [PATCH] IMA: Handle early boot data measurement

From: Mimi Zohar <zohar@linux.ibm.com>
To: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	stephen.smalley.work@gmail.com, casey@schaufler-ca.com
Cc: tyhicks@linux.microsoft.com, tusharsu@linux.microsoft.com,
	sashal@kernel.org, jmorris@namei.org,
	linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] IMA: Handle early boot data measurement
Date: Tue, 25 Aug 2020 15:43:49 -0400	[thread overview]
Message-ID: <ca5fae237a91c515147a1c03383564e0def218f7.camel@linux.ibm.com> (raw)
In-Reply-To: <958853ec-5354-fbcb-3fa0-2002954c3e40@linux.microsoft.com>

On Tue, 2020-08-25 at 12:35 -0700, Lakshmi Ramasubramanian wrote:
> On 8/25/20 11:03 AM, Mimi Zohar wrote:
> > On Tue, 2020-08-25 at 10:55 -0700, Lakshmi Ramasubramanian wrote:
> > > On 8/25/20 10:42 AM, Mimi Zohar wrote:
> > > 
> > > > > > Please limit the changes in this patch to renaming the functions and/or
> > > > > > files.  For example, adding "measure_payload_hash" should be a separate
> > > > > > patch, not hidden here.
> > > > > > 
> > > > > 
> > > > > Thanks for the feedback Mimi.
> > > > > 
> > > > > I'll split this into 2 patches:
> > > > > 
> > > > > PATCH 1: Rename files + rename CONFIG
> > > > > PATCH 2: Update IMA hook to utilize early boot data measurement.
> > > > 
> > > > I'm referring to introducing the "measure_payload_hash" flag.  I assume
> > > > this is to indicate whether the buffer should be hashed or not.
> > > > 
> > > > Example 1: ima_alloc_key_entry() and ima_alloc_data_entry(0 comparison
> > > > > -static struct ima_key_entry *ima_alloc_key_entry(struct key *keyring,
> > > > > -                                                const void *payload,
> > > > > -                                                size_t payload_len)
> > > > > -{
> > > > > +static struct ima_data_entry *ima_alloc_data_entry(const char *event_name,
> > > > > +                                                  const void *payload,
> > > > > +                                                  size_t payload_len,
> > > > > +                                                  const char *event_data,
> > > > > +                                                  enum ima_hooks func,
> > > > > +                                                  bool measure_payload_hash)  <====
> > > > > +{
> > > > 
> > > > Example 2:
> > > > diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> > > > index a74095793936..65423754765f 100644
> > > > --- a/security/integrity/ima/ima_asymmetric_keys.c
> > > > +++ b/security/integrity/ima/ima_asymmetric_keys.c
> > > > @@ -37,9 +37,10 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> > > >           if (!payload || (payload_len == 0))
> > > >                   return;
> > > >    
> > > > -       if (ima_should_queue_key())
> > > > -               queued = ima_queue_key(keyring, payload, payload_len);
> > > > -
> > > > +       if (ima_should_queue_data())
> > > > +               queued = ima_queue_data(keyring->description, payload,
> > > > +                                       payload_len, keyring->description,
> > > > +                                       KEY_CHECK, false);   <===
> > > >           if (queued)
> > > >                   return;
> > > > 
> > > > But in general, as much as possible function and file name changes
> > > > should be done independently of other changes.
> > > > 
> > > > thanks,
> > > 
> > > I agree - but in this case, Tushar's patch series on adding support for
> > > "Critical Data" measurement has already introduced
> > > "measure_payload_hash" flag. His patch updates
> > > "process_buffer_measurement()" to take this new flag and measure hash of
> > > the given data.
> > > 
> > > My patches extend that to queuing the early boot requests and processing
> > > them after a custom IMA policy is loaded.
> > > 
> > > If you still think "measure_payload_hash" flag should be introduced in
> > > the queuing change as a separate patch I'll split the patches further.
> > > Please let me know.
> > 
> > There's a major problem if his changes add new function arguments
> > without modifying all the callers of the function.  I assume the kernel
> > would fail to compile properly.
> 
> Tushar's patch series does update all the existing callers of 
> process_buffer_measurement() to handle the new arguments. His patch 
> series is self contained, and builds and works fine.

Yes, he's added "false" to existing calls.   Still, defining a new IMA
hook should be independent of adding this "measure_payload_hash"
parameter.   Each with its own patch description.

> 
> > Changing the function parameters to include "measure_payload_hash"
> > needs to be a separate patch, whether it is part of his patch set or
> > yours.
> > 
> 
> ok - I'll split the queuing patch to include "measure_payload_hash" in a 
> separate patch.

thanks,

Mimi