Re: [PATCH RFC 1/4] ipe: add the .ipe policy keyring

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

On Wed, 2026-10-28 at 14:26 +0000, Luca Boccassi wrote:
> On Wed, 28 Oct 2026 at 12:42, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > 
> > On Tue, 2026-10-27 at 11:07 +0000, Luca Boccassi wrote:
> > > On Mon, 26 Oct 2026 at 12:57, <luca.boccassi@gmail.com> wrote:
> > > > I think there is one issue with the design pattern where
> > > > keyrings are set up in userspace, that I have mentioned a few
> > > > times already and I got documented in
> > > > https://www.freedesktop.org/software/systemd/man/latest/systemd-system.conf.html#RestrictFileSystemAccess=
> > > > as well: they are trivially bypassable if the kernel has kexec
> > > > enabled and it is signed. The security model relies on the
> > > > "good" userspace running first, but if kexec is enabled,
> > > > there's no guarantee that will be the case, and as far as I can
> > > > tell it gives root trivial capability of overriding it and
> > > > extending the trust chain as the attacker wishes.
> > 
> > The attack sounds doable, but it also seems to be exploiting a gap
> > in kexec policy: kexec is supposed to behave like a warm reboot so
> > if boot policy requires UKI only then so should kexec and that
> > sounds like the thing that should be fixed.
> 
> I don't think that's the case though, even before KHO/LUO existed,
> kexec has never really behaved like a warm reboot, as for example
> boot services do not run again, so various chains of trusts are not
> reset  (eg: a bootloader might now be blocked so warm reboot would
> not work, but kexec would). And since KHO now exists, the difference
> is even greater, as more and more state is retained across the
> boundary.

But still, a lot of people are using it for servicing reboots so it
does sound as if it needs policy control.

> > What's the mechanism boot uses to ensure UKI only? So we can see if
> > it can be adopted to kexec.
> 
> There isn't one, and I don't think there is correlation, as booting a
> UKI is not the only way to boot a system. Eg: this problem applies
> just as well to booting an arm system on uboot. So I really would not
> tie this to UKI or UEFI specifics, it's more generic.

Well here's the problem: I agree root could kexec to their own initrd,
but it looks like they could also properly install and reboot to it, so
it doesn't make that much sense to plug one hole without the other (and
when they both get plugged it does make sense to use a similar
mechanism).


Regards,

James