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Re: [Qemu-devel] [PATCH 1/2] guest agent: add RPC blacklist command-line

From: Dor Laor
Subject: Re: [Qemu-devel] [PATCH 1/2] guest agent: add RPC blacklist command-line option
Date: Wed, 07 Dec 2011 14:12:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0

On 12/07/2011 12:52 PM, Daniel P. Berrange wrote:
On Wed, Dec 07, 2011 at 12:34:01PM +0200, Dor Laor wrote:
On 12/07/2011 06:03 AM, Michael Roth wrote:
This adds a command-line option, -b/--blacklist, that accepts a
comma-seperated list of RPCs to disable, or prints a list of
available RPCs if passed "?".

In consequence this also adds general blacklisting and RPC listing
facilities to the new QMP dispatch/registry facilities, should the
QMP monitor ever have a need for such a thing.

Beyond run time disablement, how easy it is to compile out some of
the general commands such as exec/file-handling?

Security certifications like common criteria usually ask to compile
out anything that might tamper security.

I don't think that's really relevant/needed. As discussed on the
call yesterday, this is security theatre, because nothing can prevent
the host admin from accessing guest RAM or disk data. AFAIK the
virtualization related security certifications acknowledge this
already&  don't make any claims about security of guests against
a malicious host admin. In any case, a suitable SELinux policy for
the guest agent could prevent arbitrary file/binary access via
generic 'exec' / 'file-read' commands, in a manner that is sufficient
to satisfy security certications.

I absolutely agree that the hypervisor can tweak the guest in multiple ways. Nevertheless there are two reasons I asked it:

 1. Reduce code and noise from security reviewers eyes.
    We were asked to do exactly that for other qemu functionality that
    is included but does not run at all. It's just makes the review

 2. Every piece of code is a risk for exploit
    Imagine that a bug/leak/use-after-free in the blacklist command or
    the exec command on qemu exists and allows attacked to gain control
    of qemu.


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