Re: [PATCH v3 00/14] KEYS: Add support for PGP keys and signatures

Ard Biesheuvel
2024-09-13T10:46:22Z

On Fri, 13 Sept 2024 at 11:32, David Howells <dhowells@redhat.com> wrote:
>
> Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> > Personally I don't think the argument above holds water. With
> > IPsec we had a similar issue of authenticating untrusted peers
> > using public key cryptography. In that case we successfully
> > delegated the task to user-space and it is still how it works
> > to this day.

This is slightly disingenuous. The kernel itself has no need to trust
the peer - it only manages the network pipe and authenticates/decrypts
the packets on behalf of user space.

The situation would be radically different if the kernel itself would
communicate over IPsec (or HTTPS) directly.

Likewise for module loading: there is no way the authentication can be
delegated to user space, unless that user space component is
authenticated by the kernel (and runs in a special, hardened context).
>
> It transpires that we do actually need at least a PGP parser in the kernel -
> and it needs to be used prior to loading any modules: some Lenovo Thinkpads,
> at least, may have EFI variables holding a list of keys in PGP form, not X.509
> form.
>
> For example, in dmesg, you might see:
>
> May 16 04:01:01 localhost kernel: integrity: Loading X.509 certificate: UEFI:MokListRT (MOKvar table)
> May 16 04:01:01 localhost kernel: integrity: Problem loading X.509 certificate -126
>

MokListRT is a shim construct, which is a component in the downstream
distro boot chain. It is not part of EFI, and in your case, this is
unlikely to be specific to Lenovo systems.

> On my laptop, if I dump this variable:
>
> efivar -e /tmp/q --name=605dab50-e046-4300-abb6-3dd810dd8b23-MokListRT
>
> And then looking at the data exported:
>
> file /tmp/q
>
> I see:
>
> /tmp/q: PGP Secret Sub-key -
>
> The kernel doesn't currently have a PGP parser. I've checked and the value
> doesn't parse as ASN.1:
>
> openssl asn1parse -in /tmp/q -inform DER
> 0:d=0 hl=2 l= 21 prim: cont [ 23 ]
> Error in encoding
> 001EBA93B67F0000:error:0680007B:asn1 encoding routines:ASN1_get_object:header too long:crypto/asn1/asn1_lib.c:105:
>
> which would suggest that it isn't X.509.
>

This should be fixed in shim not the kernel.