[libvirt][PATCH v4 0/4] Support query and use SGX

[Pavel Hrdina]

On Fri, Jul 16, 2021 at 12:58:19AM +0000, Huang, Haibin wrote:
> 
> > -----Original Message-----
> > From: Pavel Hrdina <phrdina at redhat.com>
> > Sent: Wednesday, July 7, 2021 5:48 PM
> > To: Huang, Haibin <haibin.huang at intel.com>
> > Cc: libvir-list at redhat.com; Ding, Jian-feng <jian-feng.ding at intel.com>; Yang,
> > Lin A <lin.a.yang at intel.com>; Lu, Lianhao <lianhao.lu at intel.com>
> > Subject: Re: [libvirt][PATCH v4 0/4] Support query and use SGX
> > 
> > On Thu, Jul 01, 2021 at 08:10:25PM +0800, Haibin Huang wrote:
> > > This patch series provides support for enabling Intel's Software Guard
> > Extensions (SGX) feature in guest VM.
> > >
> > > Giving the SGX support in QEMU is still pending for reviewing, this
> > > patch series is not submmited for code review, but only describe the
> > > SGX enabling solution design that contains changes to
> > virConnectGetDomainCapabilities API response and domain definition. All
> > comments/suggestions would be highly appreciated.
> > >
> > > Intel Software Guard Extensions (Intel® SGX) is a set of instructions
> > > that increases the security of application code and data, giving them
> > > more protection from disclosure or modification. Developers can partition
> > sensitive information into enclaves, which are areas of execution in memory
> > with more security protection.
> > >
> > > The typical flow looks below at very high level:
> > >
> > > 1. Calls virConnectGetDomainCapabilities API to domain capabilities that
> > includes the following SGX information.
> > >
> > > <feature>
> > > ...
> > >   <sgx supported='yes'>
> > >     <epc_size unit=’KiB’>N</epc_size>
> > >   </sgx>
> > > </feature>
> > >
> > > 2. User requests to start a guest calling virCreateXML() with SGX requirement.
> > > It should contain
> > >
> > > <launchSecurity type='sgx'>
> > >   <epc_size unit='KiB'>N</epc_size>
> > > </launchSecurity>
> > 
> > I don't think that Intel SGX belongs into <launchSecurity> in libvirt.
> > Similar feature to AMD SEV is Intel TDX which would be implement using
> > <launchSecurity> as it offers isolation between host and VM.
> > 
> > Looking at the patches this doesn't even use confidential-guest-support machine
> > option, it adds a new memory backend and enables CPU features only if libvirt
> > uses <cpu mode='custom'> so it would not work with any other CPU mode.
> > 
> > To me this sounds like we should split the feature into two components where
> > one would add support for the new memory backend into correct XML part [1]
> > and the other component would be support for CPU features related to Intel
> > SGX [2].
>
> [Haibin] ok, those specific CPU features we added have been deleted and let user to specify it in [2].
> Do we need to add new element in memory backend for SGX EPC memory?

Correct, reading QEMU and kernel patches to enable this feature in
libvirt user will need to configure SGX EPC memory backend manually.
However, we will not be able to reuse <memoryBacking> element in the VM
XML without a lot of modification to the current code. Mainly, there can
be mupltiple SGX EPC memory sections and each can have different size.
Current code allows only single <memoryBacking> file and it is closely
tied with VM RAM.

To express SGX EPC in VM XML we will need new element, for example we
can use <memory> device:

  <devices>
    ...
    <memory model='sgx-epc'>
      <target>
        <size unit='MiB'>64</size>
        <node>0</node>
      </target>
    </memory>
    ...
  </devices>

but this would require to modify the current <memory> code as the
'sgx-epc' would be a special case where we would not use '-device'
option because we need to add it to '-machine' parameter.

Another option is to create completely new element, similar to
<launchSecurity> outside of <devices> element. I'm not sure about the
naming of the new element, one thing that comes to my mind is
<memoryRegion> with type='sgx-epc'.

Based on my findings and reading different documentations and QEMU
patches it seems that in real HW the 'sgx-epc' is encrypted memory
stored within the physical RAM but in QEMU it will be additional memory
region sitting next to the VM RAM.

Adding to CC Dan, Peter, Michal to get more opinions/ideas how to design
this feature. Here is the documentation posted to QEMU list [1].

Pavel

[1] <https://lists.nongnu.org/archive/html/qemu-devel/2021-07/msg02539.html>

> > 
> > Pavel
> > 
> > [1] <https://libvirt.org/formatdomain.html#memory-backing>
> > [2] <https://libvirt.org/formatdomain.html#cpu-model-and-topology>
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