linux-kernel - Re: [PATCH v15 00/11] LSM: Three basic syscalls

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Message-ID: <c896c8ed559d0075146070be232e449b6951eb99.camel@linux.ibm.com>
Date:   Wed, 18 Oct 2023 09:09:10 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        Paul Moore <paul@...l-moore.com>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        serge@...lyn.com, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, mic@...ikod.net,
        linux-integrity@...r.kernel.org
Subject: Re: [PATCH v15 00/11] LSM: Three basic syscalls

On Wed, 2023-10-18 at 11:31 +0200, Roberto Sassu wrote:
> On Tue, 2023-10-17 at 18:07 +0200, Roberto Sassu wrote:
> > On Tue, 2023-10-17 at 11:58 -0400, Paul Moore wrote:
> > > On Tue, Oct 17, 2023 at 3:01 AM Roberto Sassu
> > > <roberto.sassu@...weicloud.com> wrote:
> > > > On Mon, 2023-10-16 at 11:06 -0400, Paul Moore wrote:
> > > > > On Mon, Oct 16, 2023 at 8:05 AM Roberto Sassu
> > > > > <roberto.sassu@...weicloud.com> wrote:
> > > > > > 
> > > > > > Sorry, I just noticed LSM_ID_IMA. Since we have the 'integrity' LSM, I
> > > > > > think it should be LSM_ID_INTEGRITY.
> > > > > > 
> > > > > > Mimi, all, do you agree? If yes, I send a patch shortly.
> > > > > 
> > > > > I believe LSM_ID_IMA is the better option, despite "integrity" already
> > > > > being present in Kconfig and possibly other areas.  "IMA" is a
> > > > > specific thing/LSM whereas "integrity" is a property, principle, or
> > > > > quality.  Especially as we move forward with promoting IMA as a full
> > > > > and proper LSM, we should work towards referring to it as "IMA" and
> > > > > not "integrity".
> > > > > 
> > > > > If anything we should be working to support "IMA" in places where we
> > > > > currently have "integrity" so that we can eventually deprecate
> > > > > "integrity".
> > > > 
> > > > Hi Paul
> > > > 
> > > > I fully understand your argument. However, 'integrity' has been the
> > > > word to identify the integrity subsystem since long time ago.
> > > > 
> > > > Reducing the scope to 'ima' would create some confusion since, while
> > > > 'ima' is associated to integrity, it would not encompass EVM.
> > > 
> > > Using LSM_ID_IMA to reference the combination of IMA+EVM makes much
> > > more sense to me than using LSM_ID_INTEGRITY, especially as we move
> > > towards promoting IMA+EVM and adopting LSM hooks for integrity
> > > verification, opening the door for other integrity focused LSMs.
> > 
> > + Mimi, linux-integrity
> > 
> > Ok, just to understand before posting v4, the code looks like this:
> 
> I worked on a new proposal. Let me know what you think. It is available
> here:
> 
> https://github.com/robertosassu/linux/tree/ima-evm-lsms-v4-devel-v6
> 
> 
> I made IMA and EVM as standalone LSMs and removed 'integrity'. They
> maintain the same properties of 'integrity', i.e. they are the last and
> always enabled.
> 
> During initialization, 'ima' and 'evm' call integrity_iintcache_init(),
> so that they can get integrity metadata. I added a check to ensure that
> this function is called only once. I also added the lsmid parameter so
> that the integrity-specific functions are added under the LSM ID of the
> caller.
> 
> I added a new LSM ID for EVM, does not look good that IMA and EVM are
> represented by LSM_ID_IMA.
> 
> Finally, I had to drop the patch to remove the rbtree, because without
> the 'integrity' LSM, space in the security blob cannot be reserved.
> Since integrity metadata is shared, it cannot be reserved by 'ima' or
> 'evm'.
> 
> An intermediate solution would be to keep the 'integrity' LSM just to
> reserve space in the security blob. Or, we remove the rbtree if/when
> IMA and EVM use disjoint integrity metadata.

One of the major benefits for making IMA and EVM LSMs was removing the
rbtree and replacing it with the ability of using i_security.

I agree with Roberto.  All three should be defined: LSM_ID_INTEGRITY,
LSM_ID_IMA, LSM_ID_EVM.

-- 
thanks,

Mimi