Re: [PATCH 1/1] kvm/speculation: Allow KVM guests to use SSBD even if host does not

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On Wed, 26 Jun 2019, Paolo Bonzini wrote:
> On 26/06/19 14:41, Thomas Gleixner wrote:
> >> I think it's better to leave the guest in control of SSBD even if it's
> >> globally disabled.  The harm cannot escape the guest and in particular
> >> it cannot escape to the sibling hyperthread.
> >
> > SSB allows guest to guest attacks IIRC
> 
> SSB requires something like
> 
>    p = &foo;
>    ...
>    p = &bar;
>    q = *p;
> 
> where "p = &foo;" is executed from one privilege domain and the others
> are executed by another process or privilege domain.  Unless two guests
> share memory, it is not possible to use it for guest-to-guest attacks.

Fair enough. It's way too hot to think clearly about these kind of problems
and there are simply way too many of them...

Thanks,

	tglx



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