Re: [RFC v2 00/27] Kernel Address Space Isolation

[Alexandre Chartre]

On 7/12/19 1:44 PM, Peter Zijlstra wrote:
> On Thu, Jul 11, 2019 at 04:25:12PM +0200, Alexandre Chartre wrote:
> > Kernel Address Space Isolation aims to use address spaces to isolate some
> > parts of the kernel (for example KVM) to prevent leaking sensitive data
> > between hyper-threads under speculative execution attacks. You can refer
> > to the first version of this RFC for more context:
> >
> >     https://lkml.org/lkml/2019/5/13/515
>
> No, no, no!
>
> That is the crux of this entire series; you're not punting on explaining
> exactly why we want to go dig through 26 patches of gunk.
>
> You get to exactly explain what (your definition of) sensitive data is,
> and which speculative scenarios and how this approach mitigates them.
>
> And included in that is a high level overview of the whole thing.

Ok, I will rework the explanation. Sorry about that.

> On the one hand you've made this implementation for KVM, while on the
> other hand you're saying it is generic but then fail to describe any
> !KVM user.
>
> AFAIK all speculative fails this is relevant to are now public, so
> excruciating horrible details are fine and required.

Ok.

> AFAIK2 this is all because of MDS but it also helps with v1.

Yes, mostly MDS and also L1TF.

> AFAIK3 this wants/needs to be combined with core-scheduling to be
> useful, but not a single mention of that is anywhere.

No. This is actually an alternative to core-scheduling. Eventually, ASI
will kick all sibling hyperthreads when exiting isolation and it needs to
run with the full kernel page-table (note that's currently not in these
patches).

So ASI can be seen as an optimization to disabling hyperthreading: instead
of just disabling hyperthreading you run with ASI, and when ASI can't preserve
isolation you will basically run with a single thread.

I will add all that to the explanation.

Thanks,

alex.