linux-kernel - Re: [PATCH 4/5] MODSIGN: checking the blacklisted hash before loading a kernel module

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Date:   Wed, 14 Mar 2018 14:08:03 +0800
From:   joeyli <jlee@...e.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        David Howells <dhowells@...hat.com>, linux-fs@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Boyer <jwboyer@...oraproject.org>
Subject: Re: [PATCH 4/5] MODSIGN: checking the blacklisted hash before
 loading a kernel module

On Tue, Mar 13, 2018 at 10:18:35AM -0700, James Bottomley wrote:
> On Tue, 2018-03-13 at 18:38 +0800, Lee, Chun-Yi wrote:
> > This patch adds the logic for checking the kernel module's hash
> > base on blacklist. The hash must be generated by sha256 and enrolled
> > to dbx/mokx.
> > 
> > For example:
> > 	sha256sum sample.ko
> > 	mokutil --mokx --import-hash $HASH_RESULT
> > 
> > Whether the signature on ko file is stripped or not, the hash can be
> > compared by kernel.
> 
> What's the use case for this?  We're already in trouble from the ODMs
> for the size of dbx and its consumption of the extremely limited
> variable space, so do we really have a use case for adding module
> blacklist hashes to the UEFI variables given the space constraints (as
> in one we can't do any other way)?
>

The dbx is a authenticated variable that it can only be updated by
manufacturer. The mokx gives a flexible way for distro to revoke a key
or a signed module. Then we don't need to touch shim or bother
manufacturer to deliver new db. Currently it doesn't have real use
case yet. 

I knew that the NVRAM has limited space. But distro needs a backup
solution for emergency.

Thanks a lot!
Joey Lee