[Xen-bugs] [Bug 215] New: linux VM crash on zero page access

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=215

           Summary: linux VM crash on zero page access
           Product: Xen
           Version: 2.0
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: critical
          Priority: P2
         Component: Guest-OS
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: staf.verhaegen@xxxxxxxxx


I'm a developer of AROS (http://www.aros.org). This is an OS modeled after the 
Amiga OS. One of 
the features is that our OS can run hosted on a linux host. I'm doing part of 
the development on a Xen 
VM provided by #unixshell. This is with there latest kernel '2.6.11.10-xenU #5'.
The problem is that running AROS can crash the whole virtual machine even when 
run as a normal 
user. The crash happens when buggy software is run on the virtual OS that 
dereferences a NULL 
pointer.
To have a virtual OS running under linux we use the signals to implement task 
switching. Amiga OS 
has also a call to disable the task switching. This call then disables certain 
signals.
I have the feeling that when there is a zero page access in such a 'disable' 
state the whole linux VM 
crashes.
I don't know how security aware xen development is at the moment but this bug 
is a local DoS attack.

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