Re: [PATCH 01/17] tpm: Define a kernel-owned TPM NV index that can't be modified by userland

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Sat, 2026-10-10 at 14:26 -0700, Matthew Garrett wrote:
[...]
> > If we do have a problem with lack of manufacturer compliance, one
> > other way I've got on my todo list is fake trusted launch: now that
> > Trenchboot is heading upstream, we have the real trusted launch,
> > but that's usually too fiddly for most people, so I was thinking if
> > we could get enough of the TXT launch to happen to open the
> > localities (without bothering too much about anything else) that
> > might be easier and give us the ability to run the Kernel in
> > locality 2.
> 
> Remember that many consumer devices don't implement TXT, it's only
> the enterprise SKUs that tend to. But that would be funny - it's the
> same sort of shape as an awful hack that's used on some of the
> Qualcomm laptops to get access to EL2.

I haven't really got much farther than a bit of dissassembly of the AC
block on the theory that if I could work out how the localities get
opened, I wouldn't even need to do a fake trusted launch.  However, I
have been doing most of the investigation on random Dell laptops, which
do claim support for TXT (at least they have a BIOS switch for it) ...
although I was looking for it now and it seems to have disappeared on
my XPS, which might be deliberate:

https://www.dell.com/community/en/conversations/xps/9730-secure-launch/6872f0a3915c657bf9d40ae2

>  Localities are very clearly the Right Way to deal with this and ugh
> if we'd been having this conversation 20 years ago instead.

Yes, I know. I actually have an unpublished patch series that makes the
kernel enforce locality 2 for its operations and 0 for userspace (to
demonstrate locality policy for keys) but because of the BIOS block it
only works on kvm guests, which makes upstreaming it a bit pointless.

Perhaps the way forward on this one is to pressure Intel and AMD to
tell us how to open the localities absent a trusted launch.  I mean, we
only need localities 0-2 which would give them an easy way to
distinguish our use case from trusted launch ... but I bet the bios
switch is all or nothing ...

Regards,

James