From mboxrd@z Thu Jan  1 00:00:00 1970
From: jlee@suse.com
Subject: Re: An actual suggestion (Re: [GIT PULL] Kernel lockdown for secure
 boot)
Date: Fri, 6 Apr 2018 00:11:24 +0800
Message-ID: <20180405161124.y5jfe76lfqog7iiv@linux-rasp2>
References: <CALCETrUVQLDC6_VEvuAbdCOuGrmcxohqTB6P8eyNojm9AryNkg@mail.gmail.com>
 <1119.1522858644@warthog.procyon.org.uk>
 <20180405021650.GC7362@linux-l9pv.suse>
 <1522936869.16421.63.camel@linux.vnet.ibm.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <1522936869.16421.63.camel@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>, Andy Lutomirski <luto@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Theodore Y. Ts'o" <tytso@mit.edu>, Matthew Garrett <mjg59@google.com>, Linus Torvalds <torvalds@linux-foundation.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, James Morris <jmorris@namei.org>, Alan Cox <gnomes@lxorguk.ukuu.org.uk>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Justin Forbes <jforbes@redhat.com>, linux-man <linux-man@vger.kernel.org>, LSM List <linux-security-module@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, Kees Cook <keescook@chromium.org>, linux-efi <linux-efi@vger.kernel.org>
List-Id: linux-api@vger.kernel.org

Hi Mimi,

On Thu, Apr 05, 2018 at 10:01:09AM -0400, Mimi Zohar wrote:
> On Thu, 2018-04-05 at 10:16 +0800, joeyli wrote:
> > Hi David, 
> > 
> > On Wed, Apr 04, 2018 at 05:17:24PM +0100, David Howells wrote:
> > > Andy Lutomirski <luto@kernel.org> wrote:
> > > 
> > > > Since this thread has devolved horribly, I'm going to propose a solution.
> > > > 
> > > > 1. Split the "lockdown" state into three levels:  (please don't
> > > > bikeshed about the names right now.)
> > > > 
> > > > LOCKDOWN_NONE: normal behavior
> > > > 
> > > > LOCKDOWN_PROTECT_INTEGREITY: kernel tries to keep root from writing to
> > > > kernel memory
> > > > 
> > > > LOCKDOWN_PROTECT_INTEGRITY_AND_SECRECY: kernel tries to keep root from
> > > > reading or writing kernel memory.
> > > 
> > > In theory, it's good idea, but in practice it's not as easy to implement as I
> > > think you think.
> > > 
> > > Let me list here the things that currently get restricted by lockdown:
> > > 
> > [...snip]
> > >  (5) Kexec.
> > >
> > 
> > About IMA with kernel module signing and kexec(not on x86_64 yet)...
> 
> Only carrying the measurement list across kexec is architecture
> specific, but everything else should work.  
> 
> > Because IMA can be used to verify the integrity of kernel module or even
> > the image for kexec. I think that the
> > IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY must be enabled at runtime
> > when kernel is locked-down.
> 
> I think we need to understand the problem a bit better.  Is the
> problem that you're using the secondary keyring and loading the UEFI
> keys onto the secondary keyring?
>

Sorry for my mistake. I want to write INTEGRITY_TRUSTED_KEYRING in
above but not IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY.

My brain is not clear when writing the mail.
 
> > Because the root can enroll master key to keyring then IMA trusts the ima key
> > derived from master key. It causes that the arbitrary signed module can be loaded
> > when the root compromised.
> 
> With only the builtin keyring, only keys signed by a builtin key can
> be added to the IMA keyring.
> 

Thanks for your description. I saw that the IMA_LOAD_X509 already depends
on IMA_TRUSTED_KEYRING (INTEGRITY_TRUSTED_KEYRING). Please ignore my concern.

Thanks a lot!
Joey Lee