Re: [Xen-devel] Xen Introspection, KPTI, and CR3 bit 63 leads to guest VMENTRY failures during introspection

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 01/25/2018 12:31 AM, Bitweasil . wrote:
> I've recently discovered that if you attempt to use introspection to
> capture CR3 changes with the new KPTI enabled kernels, the guest dies
> shortly after the start of introspection with failed VM entry due to
> invalid guest state.
> 
> I believe the invalid state here is the high bit being set in CR3 -
> while this is how one indicates that PCID should not invalidate the
> various page table caches, introspection leads to this being set in the
> VMCS, which appears to be wrong.
Our solution doesn't intercept CR3 writes (and hasn't for a while), so
it is unaffected (and this explains why we haven't come across this
issue). But the problem should clearly be solved - although at this
point it looks like the fix is somewhere deeper than the introspection
layer.


Thanks,
Razvan

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