Side-channel attacks (Meltdown, Spectre)

[Udo Steinberg]

On Fri, 5 Jan 2018 22:38:39 +0100 Alexander Boettcher (AB) wrote:

> > I am not following the recent development of all those kernels, so I
> > think it's best to directly consult the individual developers/teams for
> > statements (like the one from Stefan above).
> > 
> > For my part, I can tell you that the NOVA microhypervisor (at least the
> > official version) does not map physical RAM into the kernel virtual address
> > space, other than the RAM in which microhypervisor itself resides. NOVA maps
> > certain devices (like APIC, IOMMU), but those can't be speculatively
> > accessed anyway. I cannot comment on modified NOVA versions.  
> 
> I for my part, can confirm that the slightly, cough, modified NOVA
> version [1], as used by Genode, kept the original behavior of the
> official NOVA version [0] in that regard.

An addition after looking at the old code some more:

Note that Pd::kern, i.e. the kernel PD, actually has all physical memory
mapped 1:1, simply to have an elegant (non-special-case) way to establish
the root of the mapping hierarchy. However, no user thread ever runs in
Pd::kern, so those mappings cannot be speculatively abused.

In PDs, where user threads do run, physical memory is not mapped in the page
tables.

Cheers,
Udo
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