Re: [Qemu-devel] [PATCHv2 2/3] seccomp: adding command line support for blacklist

[Corey Bryant]

On 09/17/2013 01:14 PM, Eduardo Otubo wrote:
> On 09/17/2013 11:43 AM, Paul Moore wrote:
> > On Tuesday, September 17, 2013 02:06:06 PM Daniel P. Berrange wrote:
> > > On Tue, Sep 17, 2013 at 10:01:23AM -0300, Eduardo Otubo wrote:
> > >
> > > > Paul, what exactly are you planning to add to libvirt? I'm not a big
> > > > fan of using qemu command line to pass syscalls for blacklist as
> > > > arguments, but I can't see other way to avoid problems (like -net
> > > > bridge / -net tap) from happening.
> >
> > At present, and as far as I'm concerned pretty much everything is open
> > for
> > discussion, the code works similar to the libvirt network filters.
> > You create
> > a separate XML configuration file which defines the filter and you
> > reference
> > that filter from the domain's XML configuration.  When a QEMU/KVM or
> > LXC based
> > domain starts it uses libseccomp to create the seccomp filter and then
> > loads
> > it into the kernel after the fork but before the domain is exec'd.
>
> Clever approach. I tihnk a possible way to do this is something like:
>
>   -sandbox
> -on[,strict=<on|off>][,whitelist=qemu_whitelist.conf][,blacklist=qemu_blacklist.conf]
>
>
>      where:
>
> [,whitelist=qemu_whitelist.conf] will override default whitelist filter
> [,blacklist=blacklist.conf] will override default blacklist filter
>
> But when we add seccomp support for qemu on libvirt, we make sure to
> just add -sandbox off and use Paul's approach.
>
> Is that a reasonable approach? What do you think?

QEMU wouldn't require any changes for the approach Paul describes. The 
QEMU process that is exec'd by libvirt would be constrained by the 
filter that libvirt installed.

--
Regards,
Corey Bryant

> > There are no command line arguments passed to QEMU.  This work can
> > co-exist
> > with the QEMU seccomp filters without problem.
> >
> > The original goal of this effort wasn't to add libvirt syscall
> > filtering for
> > QEMU, but rather for LXC; adding QEMU support just happened to be a
> > trivial
> > patch once the LXC support was added.
> >
> > (I also apologize for the delays, I hit a snag with an existing
> > problem on
> > libvirt which stopped work and then some other BZs grabbed my
> > attention...)
> >
> > > IMHO, if libvirt is enabling seccomp, then making all possible cli
> > > args work is a non-goal. If there are things which require privileges
> > > seccomp is blocking, then libvirt should avoid using them. eg by making
> > > use of FD passing where appropriate to reduce privileges qemu needs.
> >
> > I agree.