Re: [Xen-users] domU kernel

[Steve Wray <steve.wray@xxxxxxxxx>]

Christian Horn wrote:
> On Fri, Oct 12, 2007 at 12:14:02AM -0400, IDAGroup - R.W.Muller wrote:
> > Hi, I found lots of threads where people talk about domU kernel sitting 
> > in /boot of dom0.
> > The only kernel I can see there is the one the machine and dom0 booted 
> > from (vmlinuz-2.6.18-8.el5xen)
> Two places are common:
> - domU-kernel placed on dom0-filesystem directly, 'kernel' option in xen-
>   config for the domU is used then. Only possible for paravirt-domU.
>   pros: - kernel is directly reachable from dom0
>   cons: - domU depends on files outside of its disc-image, so you have to 
>           keep an eye of what domU uses what kernel-file
>         - on upgrading the domU-kernel is a bit more complicated, keep
>           kernel, maybe existing initrd and modules-directory in sync
>
> - domU-kernel placed inside the domU-diskimage. Works for both HVM and
>   paravirt-domU. One sees mostly this nowadays. Kernel is located/booted
>   by pygrub (or a script mounting the partition, making a copy of the
>   kernel inside to dom0, and starting it then)
>   pros: - easy updating, i.e. just 'yum update' from the domU updates the
>           kernel, initrd, modules and kernel is booted on next domU-boot

You forgot the con.

cons: Security. You now have a domU in which a local exploit could 
result in code being executed in dom0 at the next boot of that domU. By 
the way, this actually happened. See CVE-2007-4993
IMHO putting the kernel in domU and using pygrub was always asking for 
trouble.
In my opinion it is completely crazy to expose dom0 to potential 
exploits from domU.
So far as I am aware this is the *only* way to so expose dom0 to domU 
security holes and I am deeply shocked if it is true that "One sees 
mostly this nowadays"


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