Re: [RFC Patch 0/7] kernel: Introduce multikernel architecture support

Cong Wang
2025-09-24T18:28:17Z

On Wed, Sep 24, 2025 at 5:51 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> On Wed, Sep 24, 2025 at 01:38:31PM +0200, David Hildenbrand wrote:
> > > >
> > > > Two more points:
> > > >
> > > > 1) Security lockdown. Security lockdown transforms multikernel from
> > > > "0-day means total compromise" to "0-day means single workload
> > > > compromise with rapid recovery." This is still a significant improvement
> > > > over containers where a single kernel 0-day compromises everything
> > > > simultaneously.
> > >
> > > I don't follow. My understanding is that multikernel currently does not
> > > prevent spawned kernels from affecting each other, so a kernel 0-day in
> > > multikernel still compromises everything?
> >
> > I would assume that if there is no enforced isolation by the hardware (e.g.,
> > virtualization, including partitioning hypervisors like jailhouse, pkvm etc)
> > nothing would stop a kernel A to access memory assigned to kernel B.
> >
> > And of course, memory is just one of the resources that would not be
> > properly isolated.
> >
> > Not sure if encrypting memory per kernel would really allow to not let other
> > kernels still damage such kernels.
> >
> > Also, what stops a kernel to just reboot the whole machine? Happy to learn
> > how that will be handled such that there is proper isolation.
>
> The reason I've been asking about the fault isolation and security
> statements in the cover letter is because it's unclear:
> 1. What is implemented today in multikernel.
> 2. What is on the roadmap for multikernel.
> 3. What is out of scope for multikernel.
>
> Cong: Can you clarify this? If the answer is that fault isolation and
> security are out of scope, then this discussion can be skipped.

It is my pleasure. The email is too narrow, therefore I wrote a
complete document for you:
https://docs.google.com/document/d/1yneO6O6C_z0Lh3A2QyT8XsH7ZrQ7-naGQT-rpdjWa_g/edit?usp=sharing

I hope it answers all of the above questions and provides a clear
big picture. If not, please let me know.

(If you need edit permission for the above document, please just
request, I will approve.)

Regards,
Cong Wang