Re: [Linux-ima-user] Initramfs and IMA Appraisal

Mimi Zohar
2014-12-30T03:06:34Z

On Mon, 2014-12-29 at 18:25 -0800, David Lang wrote:
> On Mon, 29 Dec 2014, Mimi Zohar wrote:
>
> > Thanks Rob for the explanation. The problem is that ramfs does not
> > support extended attributes, while tmpfs does. The boot loader could
> > "measure" (trusted boot) the initramfs, but as the initramfs is
> > generated on the target system, the initramfs is not signed, preventing
> > it from being appraised (secure Boot). To close the initramfs integrity
> > appraisal gap requires verifying the individual initramfs file
> > signatures, which are stored as extended attributes.
>
> what's the point of checking the files on the filesystem against signatures
> stored on the same filesystem? If someone could alter the file contents they can
> alter the signatures as well.

It's all about limiting which public keys can be used to verify the file
signatures. As of 3.17, only keys signed by a "trusted" key on the
system keyring may be added to the IMA keyring.

Mimi