linux-kernel - Re: [PATCH v4 00/12] Enroll kernel keys thru MOK

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Message-ID: <335ba50bcb9069faac135bce77c6f7ba19bd90ca.camel@kernel.org>
Date:   Mon, 23 Aug 2021 20:35:57 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        keyrings@...r.kernel.org, linux-integrity@...r.kernel.org,
        dhowells@...hat.com, dwmw2@...radead.org,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        jmorris@...ei.org, serge@...lyn.com
Cc:     keescook@...omium.org, gregkh@...uxfoundation.org,
        torvalds@...ux-foundation.org, scott.branden@...adcom.com,
        weiyongjun1@...wei.com, nayna@...ux.ibm.com, ebiggers@...gle.com,
        ardb@...nel.org, nramas@...ux.microsoft.com, lszubowi@...hat.com,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James.Bottomley@...senPartnership.com, pjones@...hat.com,
        konrad.wilk@...cle.com, Patrick Uiterwijk <patrick@...terwijk.org>
Subject: Re: [PATCH v4 00/12] Enroll kernel keys thru MOK

On Thu, 2021-08-19 at 09:10 -0400, Mimi Zohar wrote:
> On Thu, 2021-08-19 at 14:38 +0300, Jarkko Sakkinen wrote:
> > On Wed, 2021-08-18 at 20:20 -0400, Eric Snowberg wrote:
> > > Many UEFI Linux distributions boot using shim.  The UEFI shim provides
> > > what is called Machine Owner Keys (MOK).  Shim uses both the UEFI Secure
> > > Boot DB and MOK keys to validate the next step in the boot chain.  The
> > > MOK facility can be used to import user generated keys.  These keys can
> > > be used to sign an end-user development kernel build.  When Linux boots,
> > > pre-boot keys (both UEFI Secure Boot DB and MOK keys) get loaded in the
> > > Linux .platform keyring.  
> > > 
> > > Currently, pre-boot keys are not trusted within the Linux trust boundary
> > > [1]. These platform keys can only be used for kexec. If an end-user
> > > wants to use their own key within the Linux trust boundary, they must
> > > either compile it into the kernel themselves or use the insert-sys-cert
> > > script. Both options present a problem. Many end-users do not want to
> > > compile their own kernels. With the insert-sys-cert option, there are
> > > missing upstream changes [2].  Also, with the insert-sys-cert option,
> > > the end-user must re-sign their kernel again with their own key, and
> > > then insert that key into the MOK db. Another problem with
> > > insert-sys-cert is that only a single key can be inserted into a
> > > compressed kernel.
> > > 
> > > Having the ability to insert a key into the Linux trust boundary opens
> > > up various possibilities.  The end-user can use a pre-built kernel and
> > > sign their own kernel modules.  It also opens up the ability for an
> > > end-user to more easily use digital signature based IMA-appraisal.  To
> > > get a key into the ima keyring, it must be signed by a key within the
> > > Linux trust boundary.
> > 
> > As of today, I can use a prebuilt kernel, crate my own MOK key and sign
> > modules. What will be different?
> 
> The UEFI db and MOK keys are being loaded onto the .platform keyring,
> which is suppose to be limited to verifying the kexec kernel image
> signature.  With a downstream patch, kernel modules are being verified
> as well.
> 
> Initially Patrick Uiterwijk's "[PATCH 0/3] Load keys from TPM2 NV Index
> on IMA keyring" patch set attempted to define a new root of trust based
> on a key stored in the TPM.  This patch set is similarly attempting to
> define a new root of trust based on CA keys stored in the MOK db.
> 
> The purpose of this patch set is to define a new, safe trust source
> parallel to the builtin keyring, without relying on a downstream patch.
> With the new root of trust, the end user could sign his own kernel
> modules, sign third party keys, and load keys onto the IMA keyring,
> which can be used for signing the IMA policy and other files.

I can, as of today, generate my own mok key and sign my LKM's, and
kernel will verify my LKM's.

What is different?


/Jarkko