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Re: [Xen-users] domU kernel

  • To: "IDAGroup - R.W.Muller" <robin@xxxxxxxxxxx>
  • From: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
  • Date: Mon, 15 Oct 2007 07:46:08 +0100
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Sun, 14 Oct 2007 23:40:16 -0700
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CentOS didn't do this! RedHat did it this way, CentOS is a rebuild of RHEL.

IDAGroup - R.W.Muller wrote:
Wow, if that is true then is CentOS making a big mistake.
When I installed CentOS with virtualization and started virt-install according to there howto, I was guided to install another CentOS domU but never asked to have a kernel outside the domU.

So, I just even realized that this is possible, when I was reading this user list, before I thought the CentOS way is the only possibility ...so clearly: kernel IN domU

Steve Wray wrote:
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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