On 31 January 2017 at 18:59, David Howells [off-list ref] wrote:

Ard Biesheuvel [off-list ref] wrote:

quoted

quoted

UEFI-2.6 adds a new variable, DeployedMode.  If it exists, this must be 1
if we're to engage lockdown mode.

Reported-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: David Howells <dhowells@redhat.com>

Interestingly, the string 'DeployedMode' appears zero times in the
EDK2 codebase, so I wonder if it makes any sense to merge this now.
The string 'AuditMode' does appear once, but in a comment

It's in the standard, so shouldn't we check for it?

quoted

In any case, the logic is not entirely correct either: apologies if it
was me who caused any confusion here, but it seems DeployedMode could
legally be 0 or 1 while secure boot is in fact enabled. It is actually
AuditMode that should be taken into account here, i.e., if AuditMode
== 1, the firmware ignores invalid or missing signatures. If
SecureBoot == 0x1, SetupMode == 0x0 and AuditMode == 0x0 (or
non-existent), signature verification is performed regardless of the
value (or existence) of DeployedMode.

So I propose to respin this patch to treat AuditMode == 0x1 as 'secure
boot disabled', and ignore if it is missing.

Ummm...  This might conflict what said:

| Since you seem to be using this to mean "is the platform locked down?",
| this looks to be no longer complete in the UEFI 2.6 world.  If
| DeployedMode == 0, even if SecureBoot == 1 and SetupMode == 0, you can
| remove the platform key by writing 1 to AuditMode and gain control of
| the secure variables.  The lock down state becomes DeployedMode == 1,
| SecureBoot == 1 and SetupMode == 0
|
| See the diagram on page 1817
|
| http://www.uefi.org/sites/default/files/resources/UEFI%20Spec%202_6.pdf

Looking again at that diagram, should I be checking all four variables
(SecureBoot, SetupMode, DeployedMode and AuditMode)?  And/or should I treat
audit mode differently to deployed mode?

Well, we are trying to decide whether the system is locked down or
not. AuditMode is only writable before ExitBootServices(), and when
AuditMode == 0, signature verification occurs as usual, regardless of
the value of DeployedMode. Whether someone could turn on AuditMode on
the *next* boot does not sound that relevant to me, since someone
could also re-enter SetupMode in the same way.

So this patch should take AuditMode into account, but not DeployedMode, i.e.,

SecureBoot == 0x1
SetupMode == 0x0
AuditMode == 0x0 (or non-existent)

implies a locked down state.

Further, there doesn't seem to be a state in which SecureBoot is shown as
being 1.

Yes, that is sloppy. But the fact that EDK2, being the v2.6 reference,
does not implement any of this *at all* is much more worrying to me,
given that UDK2017 based firmware will certainly turn up in production
systems.