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Subject: Re: [PATCH v9 2/8] integrity: Introduce a Linux keyring called
 machine
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>,
        Eric Snowberg <eric.snowberg@oracle.com>
Cc:     David Howells <dhowells@redhat.com>,
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        "keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
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        Konrad Wilk <konrad.wilk@oracle.com>
Date:   Sat, 15 Jan 2022 21:55:47 -0500
In-Reply-To: <YeMdY+FLM32tmRMz@iki.fi>
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On Sat, 2022-01-15 at 21:15 +0200, Jarkko Sakkinen wrote:
> On Sat, Jan 15, 2022 at 09:14:45PM +0200, Jarkko Sakkinen wrote:
> > On Sat, Jan 15, 2022 at 07:12:35PM +0000, Eric Snowberg wrote:
> > > 
> > > 
> > > > On Jan 15, 2022, at 10:11 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > > > 
> > > > On Wed, Jan 12, 2022 at 02:41:47PM -0500, Mimi Zohar wrote:
> > > >> On Tue, 2022-01-11 at 20:14 -0500, Mimi Zohar wrote:
> > > >>> On Tue, 2022-01-11 at 21:26 +0000, Eric Snowberg wrote:
> > > >>>> 
> > > >>>>> On Jan 11, 2022, at 11:16 AM, Mimi Zohar <zohar@linux.ibm.com> wrote:
> > > >>>>> 
> > > >>>>> On Mon, 2022-01-10 at 23:25 +0000, Eric Snowberg wrote:
> > > >>>>>>> Jarkko, my concern is that once this version of the patch set is
> > > >>>>>>> upstreamed, would limiting which keys may be loaded onto the .machine
> > > >>>>>>> keyring be considered a regression?
> > > >>>>>> 
> > > >>>>>> 
> > > >>>>>> Currently certificates built into the kernel do not have a CA restriction on them.  
> > > >>>>>> IMA will trust anything in this keyring even if the CA bit is not set.  While it would 
> > > >>>>>> be advisable for a kernel to be built with a CA, nothing currently enforces it. 
> > > >>>>>> 
> > > >>>>>> My thinking for the dropped CA restriction patches was to introduce a new Kconfig.  
> > > >>>>>> This Kconfig would do the CA enforcement on the machine keyring.  However if the 
> > > >>>>>> Kconfig option was not set for enforcement, it would work as it does in this series, 
> > > >>>>>> plus it would allow IMA to work with non-CA keys.  This would be done by removing 
> > > >>>>>> the restriction placed in this patch. Let me know your thoughts on whether this would 
> > > >>>>>> be an appropriate solution.  I believe this would get around what you are identifying as 
> > > >>>>>> a possible regression.
> > > >>>>> 
> > > >>>>> True the problem currently exists with the builtin keys, but there's a
> > > >>>>> major difference between trusting the builtin keys and those being
> > > >>>>> loading via MOK.  This is an integrity gap that needs to be closed and
> > > >>>>> shouldn't be expanded to keys on the .machine keyring.
> > > >>>>> 
> > > >>>>> "plus it would allow IMA to work with non-CA keys" is unacceptable.
> > > >>>> 
> > > >>>> Ok, I’ll leave that part out.  Could you clarify the wording I should include in the future 
> > > >>>> cover letter, which adds IMA support, on why it is unacceptable for the end-user to
> > > >>>> make this decision?
> > > >>> 
> > > >>> The Kconfig IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
> > > >>> "help" is very clear:
> > > >> 
> > > >> [Reposting the text due to email formatting issues.]
> > > >> 
> > > >> help
> > > >>  Keys may be added to the IMA or IMA blacklist keyrings, if the
> > > >>  key is validly signed by a CA cert in the system built-in or
> > > >>  secondary trusted keyrings.
> > > >> 
> > > >>  Intermediate keys between those the kernel has compiled in and the 
> > > >>  IMA keys to be added may be added to the system secondary keyring,
> > > >>  provided they are validly signed by a key already resident in the
> > > >>  built-in or secondary trusted keyrings.
> > > >> 
> > > >> 
> > > >> The first paragraph requires "validly signed by a CA cert in the system
> > > >> built-in or secondary trusted keyrings" for keys to be loaded onto the
> > > >> IMA keyring.  This Kconfig is limited to just the builtin and secondary
> > > >> keyrings.  Changing this silently to include the ".machine" keyring
> > > >> introduces integrity risks that previously did not exist.  A new IMA
> > > >> Kconfig needs to be defined to allow all three keyrings - builtin,
> > > >> machine, and secondary.
> > > >> 
> > > >> The second paragraph implies that only CA and intermediate CA keys are
> > > >> on secondary keyring, or as in our case the ".machine" keyring linked
> > > >> to the secondary keyring.
> > > >> 
> > > >> Mimi
> > > >> 
> > > > I have also now test environment for this patch set but if there are
> > > > any possible changes, I'm waiting for a new version, as it is anyway
> > > > for 5.18 cycle earliest.
> > > 
> > > Other than the two sentence changes, I have not seen anything identified 
> > > code wise requiring a change.  If you’d like me to respin a v10 with the sentence 
> > > changes let me know.  Or if you want to remove the ima reference, that works 
> > > too.  Just let me know how you want to handle this.  Thanks.
> > 
> > I'm basically waiting also Mimi to test this as I do not have IMA test
> > environment.
> > 
> > From my side:
> > 
> > Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
> 
> I can pick the whole thing at the time when I get green light.

The MOK keys are not loaded onto the .machine keyring if
CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY is enabled. 
From an IMA perspective nothing has changed.

After the IMA references in the patch descriptions are removed, feel
free to add Tested-by: Mimi Zohar <zohar@linux.ibm.com> on patches 1 -
5.

thanks,

Mimi