Xen project Mailing List

Re: [Xen-devel] [Hackathon 16] Notes from Security Session

On 19/04/16 10:02, Doug Goldstein wrote:

On 4/18/16 12:20 PM, Lars Kurth wrote:

Hi all,

I took notes as much as I could. CC'ed the people who participated most. If I 
missed/misrepresented something, please add to the discussion. I know that 
George for example took some extra notes in the one or other area.

Regards
Lars

== Topics discussed ==
QEMU
De-privilige of QEMU
XSA
x-Splice
x86 Emulator
Enabling XSM By default

=== Slimline QEMU ===

Konrad: Some inroads on making QEMU better
Konrad: QEMU is too big and it is hard to strip down the platform : how can we 
chop it up

Wei: Wei attempted this 2 years ago : Wei defined some Xen stub CPU model, 
which was rejected at the time
Stefano: Maybe what we need is different
Stefano: Containers / Intel have similar issues
Stefano: Intel have a very similar problem with ClearContainer
Stefano: Re-implementing ClearContainers with QEMU because of market needs
Stefano: QEMU does have already a no-default option

Doug: In the QEMU model: you cannot run a board without a CPU
Doug: KConfig may be acceptable, but re4moving boards may not (initially 
discussed with Antony L)

George: Distros don't want to ship two versions of QEMU
George: Compile configurability doesn't help with distros

Konrad: PVH/HVMLite does not use QEMU (or only as a back)

Lars: If we had a proposal, working with Intel and the QEMU community, we could 
discuss at Xen Summit / KVM Forum is co-located

James: If we had a future with OVMF, then we probably wouldn't need QEMU (aka 
if you want security use PVH with OVMF)
James: Proposal for security conscious applications we could fork and use a 
stubbed out version of QEMU

Options:
- KConfig
- Run-time disablement
- Xen Summit / KVM Forum
- Intel work / collaboration
- PIX3 > 935
- OVMF
- Remove xl.cfg (stop configs - in fact we probably only can print a warning "this 
is not secure and has no security support" or something similar)

Doug: Issue
- For example Oracle could deal with Config
- BUT, this approach won't work for distros

ACTION: Konrad is volunteering to drive this discussion

=== De-privilige Qemu ===
Konrad: What's the status
Stefano: not done, you need
- QEMU as non-root (that is in 4.7 and QEMU part is there)
- Now you still have a libxc and xenstore interface that needs to be 
de-priviliged
   - There is a patch for QEMI and xenstore to deal with the libxc part (not 
upstreamed) ... pretty big series, but won't make it for 4.7 - QEMU part is tiny
   - Libxc is sizeable (Ian Campbell was working on it), but it is now dormant 
: QEMU support is there, but Dom0 interface is missing
     - Ideas: Do registration in Dom0
[George has some additional notes]

ISSUE: A proposal and a plan, but nobody to do this. Without this what we have 
is not useful
Andrew: XenServer still using qemu-trad because of some gaps in emu-upstream
Andrew: XS may end up working on this at some undefined point in the future

There is a problem with using CD drive's to open ISOs as you need to be 
privileged to do this
Andy Cooper: there may be real end-user issues
Stefano: Could change ownership
Doug: Issue was tried to be fixed in libvirt and went nowhere
Andy: Qemu-trad does it wrong (QEMU in libxenlight does not do that)

ACTION: High;right lack of owner

Konrad: Seccomp may work
Doug: everything has to be passed as file descriptor

=== Narrower XSA Coverage ===
Jan: XSA 77 (whitelisted a set of dom control and sys control) which are 
supposedly ... http://xenbits.xen.org/xsa/advisory-77.html
      See http://xenbits.xen.org/docs/unstable/misc/xsm-flask.txt (Security 
Status of dom0 disaggregation)
Jan: Who runs this in production: running part of toolstack not in Dom0 - 
OpenXT wants to do this
Jan: The observation is that we went to far with the XSA 77 => if we had a 
shorter whitelist, and reduce whitelist
Jan: If there was agreement, then the security team
  would not handle issues in these areas as XSA's

Ross Phillipson: Typic ally we have only higher level stuff in a different xl, 
but lower level stuff runs on Dom0. So there should be no issue

George: QEMU stub domains should have security support
George: There are a whole set of other things, which we don't know whether they 
are used
George: Do we want to security support of disaggregated tools-stub

Agreed: Propose patch to change 
http://xenbits.xen.org/docs/unstable/misc/xsm-flask.txt on the list
Jan: We can only discuss in public if no issues are pending
Cc: Christopher Clark <christopher.w.clark@xxxxxxxxx>, Ross Philipson 
<ross.philipson@xxxxxxxxx>, Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
CC the folks on this thread or openxt@xxxxxxxxxxxxxxxx (OpenXT mailing list)

=== x86 Emulation de-privilige ===
Anthony is working on it
Stefano: I think you had some measurements
Anthony: Measurements were not very good
Andrew: If you are introspecting, you sacrifice 70% performance
Andrew: Patches were very complicated
Andrew: Re-writing the emulator would only fix the outbound path
Stefano: Risk would probably go from High/Critical to Low in terms of impact 
but not remove the issues
Jan: The issue is really with in-guest security issues
Doug: Could we look at QEMU emulator
Andrew: Did this, but does not seem a good enough baseline
James: Have a set of patches which may fix this issue
Jan: Would still not fix in-guest security issues
Andrew: Reduces the severity of XSAs

Konrad: We still want this?
Jan: If it is doable, then yes ...
Andrew: Huge amount of extra set-up in HV

ACTION: James to sent patches as RFC to xen-devel@

Jan: The real issue is the quality and maintainability of emulator code
Konrad: Two paths - emulator code more robust or de-privilege emulator


=== x-Splice ===
Konrad: At some point, we can provide catches for which we can create payloads
Konrad: There are areas which are difficult to do, such as patching data
Konrad: Questions - if we had xSplice - should we publish patches to generate the 
"payload" and as we have in the past

Andrew: believes that there are only a small number of XSA's that could not 
easily be changed into payloads

Agreement: do this as a best-effort

James: Asks whether chaining patches is an issue
Konrad: No issues, but you should deploy binary patches ...

Konrad: Can you deploy
Jan: Same as with deploying binaries
Lars: Could just change the boilerplate

Ross: Is there a way to encode dependencies
Konrad: Yes

=== Enabling XSM By default ===
Andrew: There are some issues which we need to work through; a lot of little 
paper cuts
Rich: Could we create a list of issues on the wiki?
Lars: Definitely
Doug: Could we not have a policy which is equivalent to XSM being compiled out
Andrew: Could make policy more modular instead of one big global policy

Re-apply policy of guest after running

ACTION: Need a wiki page, Konrad can start one and we can collaboratively flesh 
it out
Lars: See http://wiki.xenproject.org/wiki/XSMAsDefault_TODO_List

ACTION: Konrad and others to add detail to it

It was pointed out to me that I did not get my comments about XSM across
clearly. I believe we need to improve the default policy to be
equivalent to disabling XSM and/or create a policy called "dummy" that
is the same as XSM disabled. To make XSM usage more smooth I propose we
bake the default policy into .initdata so that when you boot Xen
compiled with XSM you are no worse off than compiling XSM out.

The rationale here is that prior to a recent commit when you compiled
Xen with XSM enabled but did not provide a default policy then any domUs
that you ran had as much access as dom0. The recent commit changed it so
that Xen by default does not boot without a policy.

With my proposed change we would have "dummy" that would compile in and
if you provided another policy it would be used instead or you could
late load a replacement policy. Basically filling the gap of turning on
XSM and having a system less secure than XSM off until you developed
your policy.

+1. It also avoids needing to play around loading an extra file as a

grub module, which makes distro-integration easer.

~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

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