Re: [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, Jan 27, 2021 at 09:03:59AM -0500, Mimi Zohar wrote:
> [Cc'ing linux-integrity]
> 
> On Wed, 2021-01-27 at 11:46 +0000, David Howells wrote:
> > Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > 
> > > > I suppose a user space tool could be created. But wouldn’t what is
> > > > currently done in the kernel in this area need to be removed?
> > > 
> > > Right. I don't think this was a great idea in the first place to
> > > do to the kernel but since it exists, I guess the patch does make
> > > sense.
> > 
> > This information needs to be loaded from the UEFI tables before the system
> > starts loading any kernel modules or running any programs (if we do
> > verification of such, which I think IMA can do).
> 
> There needs to a clear distinction between the pre-boot and post-boot
> keys.  UEFI has its own trust model, which should be limited to UEFI. 
> The .platform keyring was upstreamed and limited to verifying the kexec
> kernel image.   Any other usage of the .platform keyring keys is
> abusing its intended purpose.
> 
> The cover letter says,   "Anytime the .platform keyring is used, the
> keys in the .blacklist keyring are referenced, if a matching key is
> found, the key will be rejected."   I don't have a problem with loading
> the UEFI X509 dbx entries as long as its usage is limited to verifying
> the kexec kernel image.
> 
> Mimi

Thanks Mimi, this is a valid argument. I agree.

/Jarkko