[libvirt] [PATCH] docs: kbase: Add a section explaining how to verify SEV from the guest

[Daniel P. Berrangé]

On Fri, Sep 20, 2019 at 01:47:09PM +0200, Erik Skultety wrote:
> Commit 50dfabbb59 forgot to add this important bit on how to check that
> all the changes to the XML actually worked.
> ---
>  docs/kbase/launch_security_sev.html.in | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/docs/kbase/launch_security_sev.html.in b/docs/kbase/launch_security_sev.html.in
> index 923bb52b25..4b8e06ccc1 100644
> --- a/docs/kbase/launch_security_sev.html.in
> +++ b/docs/kbase/launch_security_sev.html.in
> @@ -349,6 +349,18 @@ EOF</pre>
>    ...
>  </domain></pre>
> 
> +    <h2><a id="Guest">Checking SEV from within the guest</a></h2>
> +    <p>
> +        After making the necessary adjustments discussed in
> +        <a href="#Configuration">Configuration</a>, the VM should now boot
> +        successfully with SEV enabled. You can then verify that the guest
> +        enabled with SEV by running:
> +    </p>
> +
> +    <pre>
> +# dmesg | grep -i sev
> +AMD Secure Encrypted Virtualization (SEV) active</pre>
> +

My understanding of SEV, was that it should be impossible to boot the
SEV enabled kernel at all if SEV was not active on the host.

Given SEV is a security critical mechanism though, looking at kernel dmesg
doesn't feel like a satisfactory approach for validating the host really
did boot your SEV enabled kernel, as opposed to replacing it with a backdoor
kernel which simply prints this magic to dmesg.

So I'm wondering what really is the secure way to unambigously prove that
you've booted the original SEV enabled kernel & not an imposter ?

Regards,
Daniel
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