linux-kernel - Re: [PATCH 0/2 v3] kvm: notify host when guest panicked

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Date:	Wed, 14 Mar 2012 10:59:14 +0000
From:	"Daniel P. Berrange" <berrange@...hat.com>
To:	Wen Congyang <wency@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, Amit Shah <amit.shah@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 0/2 v3] kvm: notify host when guest panicked

On Wed, Mar 14, 2012 at 06:58:47PM +0800, Wen Congyang wrote:
> At 03/14/2012 06:52 PM, Avi Kivity Wrote:
> > On 03/14/2012 12:52 PM, Wen Congyang wrote:
> >>>
> >>>> If so, is this channel visible to guest userspace? If the channle is visible to guest
> >>>> userspace, the program running in userspace may write the same message to the channel.
> >>>
> >>> Access control is via permissions.  You can have udev scripts assign
> >>> whatever uid and gid to the port of your interest.  By default, all
> >>> ports are only accessible to the root user.
> >>
> >> We should also prevent root user writing message to this channel if it is
> >> used for panicked notification.
> >>
> > 
> > Why?  root can easily cause a panic.
> > 
> 
> root user can write the same message to virtio-serial while the guest is running...

Unless you are running a MAC policy which strictly confines the root
account, root can cause a kernel panic regardless of virtio-serial
permissions in the guest:

  echo c > /proc/sysrq-trigger

Regards,
Daniel
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