On Mon, 2016-11-21 at 11:25 -0500, Josh Boyer wrote: > On Mon, Nov 21, 2016 at 11:16 AM, Ard Biesheuvel > <ard.biesheu...@linaro.org> wrote: > > On 16 November 2016 at 18:11, David Howells <dhowe...@redhat.com> > > wrote: > > > From: Josh Boyer <jwbo...@fedoraproject.org> > > > > > > Secure Boot stores a list of allowed certificates in the 'db' > > > variable. This imports those certificates into the system trusted > > > keyring. This allows for a third party signing certificate to > > > be used in conjunction with signed modules. By importing the > > > public certificate into the 'db' variable, a user can allow a > > > module signed with that certificate to load. The shim UEFI > > > bootloader has a similar certificate list stored in the > > > 'MokListRT' variable. We import those as well. > > > > > > > This sounds like a bad idea to me. For the standard databases like > > db and dbx, we can rely on the firmware to ensure that they are > > what you expect. For MokListRt, not so much: anyone with sufficient > > capabilities can generate such a variable from userland, and not > > every arch/distro combo will be using shim and/or mokmanager. (The > > debates are still ongoing, but my position is that there is no need > > for shim at all on ARM given that the M$ problem only exists on > > x86) > > In order for MokListRT to be modified, the user has to have physical > access and boot into Mok and complete the enrollment. That is no > different than simply enrolling in db or dbx. I don't see a > difference in security under the thread model that Secure Boot is > attempting to protect against.
Isn't a potential attack to write to MokListRT and then force a kexec? That means shim doesn't validate the variable yet you treat it as though it has been validated. James
