Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc_page()

Sean Christopherson
2021-03-23T16:52:01Z

On Tue, Mar 23, 2021, Borislav Petkov wrote:
> On Tue, Mar 23, 2021 at 04:21:47PM +0000, Sean Christopherson wrote:
> > I like the idea of pointing at the documentation. The documentation should
> > probably emphasize that something is very, very wrong.
>
> Yap, because no matter how we formulate the error message, it still ain't enough
> and needs a longer explanation.
>
> > E.g. if a kernel bug triggers EREMOVE failure and isn't detected until
> > the kernel is widely deployed in a fleet, then the folks deploying the
> > kernel probably _should_ be in all out panic. For this variety of bug
> > to escape that far, it means there are huge holes in test coverage, in
> > both the kernel itself and in the infrasturcture of whoever is rolling
> > out their new kernel.
>
> You sound just like someone who works at a company with a big fleet, oh
> wait...
>
> :-)
>
> And yap, you big fleeted guys will more likely catch it but we do have
> all these other customers who have a handful of servers only so they
> probably won't be able to do such a wide coverage.

The size of the fleet shouldn't matter for this specific case. This bug
requires the _host_ to be running enclaves, and obviously it also requires the
system to be running SGX-enabled guests as well. In such a setup, the SGX
workload running in the host should be very well defined and understood, i.e.
testing should be a well-bounded problem to solve.

Running enclaves in both the host and guest should be uncommon in and of itself,
and for such setups, running _any_ SGX workloads in the host, let alone more
than 1 or 2 unique workloads, without ensuring guests are fully isolated is,
IMO, insane.

But yeah, what can happen, will happen.

> So I hope they'll appreciate this longer explanation about what to do
> when they hit it. And normally I wouldn't even care but we almost never
> tell people to reboot their boxes to fix sh*t - that's the other OS.
>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette