Re: [Xen-devel] [PATCH] xenballoond (memory overcommit) scripts

["viets@xxxxxxx" <viets@xxxxxxx>]

Hey,

ok, you're right, but I thought to change a kernel is harder than
changing a skript on a domU...

Your script inspired me to make an own script working on dom0, it isn't
beautiful, but my first test were successfully, tomorrow I will test it
more.

I will post my script just to know whether it is worth to improve it.

First of all I changed the DomU kernel, that I've got the Memory
Information over xenbus.

/linux-2.6.18-xen.hg-xenU.bak/fs/proc/proc_misc.c
54a55,58
> //Edited by me
> #include <xen/xenbus.h>
> //Edited by me
>
205a210,216
> //Edited by Me
>               (void)xenbus_printf(XBT_NIL, "memory", "Committed_AS",
>                                 "%lu", K(committed) );
>               (void)xenbus_printf(XBT_NIL, "memory", "MemTotal",
>                                 "%lu", K(i.totalram) );
> //Edited by Me
>

After that I just edit your script, as I say it is not finished, but
just wanna post it for feedback..

#/bin/bash

curkb() {
  kb=$(xenstore-read /local/domain/$1/memory/MemTotal);
  RETVAL=$kb
  return  # value returned in RETVAL in kB
}

downhysteresis() {
#       RETVAL=$XENBALLOON_AUTO_DOWNHYSTERESIS
#       if [ $xenstore_enabled = "true" ]; then
#               if xenstore-exists memory/downhysteresis ; then
#                       RETVAL=`xenstore-read memory/downhysteresis`
#               fi
#       fi
  RETVAL=10;
  return;
}

uphysteresis() {
#  RETVAL=$XENBALLOON_AUTO_UPHYSTERESIS
#       if [ $xenstore_enabled = "true" ]; then
#               if xenstore-exists memory/uphysteresis ; then
#                       RETVAL=`xenstore-read memory/uphysteresis`
#               fi
#       fi
  RETVAL=1;
  return
}

minmb() {
  RETVAL=$XENBALLOON_MINMEM;
  if [ $RETVAL -ne 0 ]; then
   return $RETVAL
  fi
  kb=$(cat $maxkb);
  let "mb=$kb/1024";
  let "pages=$kb/4";
  # this algorithm from drivers/xen/balloon/balloon.c:minimum_target()
  # which was added to balloon.c in 2008 to avoid ballooning too small
  # it is unnecessary here except to accomodate pre-2008 balloon drivers
  # note that ranges are adjusted because a VM with "memory=1024"
  # gets somewhat less than 1024MB
  if [ $mb -lt 125 ]; then
    let RETVAL="$(( 8 + ($pages >> 9) ))"
  elif [ $mb -lt 500 ]; then
    let RETVAL="$(( 40 + ($pages >> 10) ))"
  elif [ $mb -lt 2000 ]; then
    let RETVAL="$(( 104 + ($pages >> 11) ))"
  else
    let RETVAL="$(( 296 + ($pages >> 13) ))"
  fi
  return        # value returned in RETVAL in mB
}

selftarget() {
  tgtkb=$(xenstore-read /local/domain/$1/memory/Committed_AS);
  minmb;
  let "minbytes=$RETVAL*1024*1024";
  let "tgtbytes=$tgtkb*1024";
  if [ $tgtbytes -lt $minbytes ]; then
    let "tgtbytes=$minbytes";
  fi
  RETVAL=$tgtbytes  # value returned in RETVAL in bytes
  return
}

balloon_to_target() {
  if [ "$2" -eq 1 ]; then
    selftarget $1;
    tgtbytes=$RETVAL;
   else
     let "tgtbytes=$(( $1 * 1024 ))";
  fi;
    curkb $1;
    let "curbytes=$RETVAL*1024"
    if [ $curbytes -gt $tgtbytes ]; then
      downhysteresis;
      downhys=$RETVAL
      if [ $downhys -ne 0 ]; then
        let "tgtbytes=$(( $curbytes - \
        ( ( $curbytes - $tgtbytes ) / $downhys ) ))"
      fi
    else if [ $curbytes -lt $tgtbytes ]; then
      uphysteresis
      uphys=$RETVAL
      let "tgtbytes=$(( $curbytes + \
      ( ( $tgtbytes - $curbytes ) / $uphys ) ))"
    fi
  fi
  let "tgt=$(( $tgtbytes/1024/1024 ))";
  xm mem-set $1 $tgt;
  let "tgtkb=$(( $tgtbytes/1024 ))"
  xenstore-write /local/domain/$1/memory/selftarget $tgtkb
}

selfballoon_eval() {
  if xenstore-exists /local/domain/$1/memory/selfballoon; then
    RETVAL=$(xenstore-read /local/domain/$1/memory/selfballoon);
    if [ $RETVAL -eq 1 ]; then
      selfballoon_enabled=true;
      return;
    fi;
  fi;
  selfballoon_enabled=$XENBALLOON_SELF;
  return;
}

maxkb=1073741824;

. /etc/sysconfig/xenballoon.conf

while true; do
  for i in $(xm list | awk '{print $2;'} | fgrep -v 'ID' | fgrep -v '0'); do
#    curkb=$(xenstore-read /local/domain/$i/memory/MemTotal);
    selfballoon_eval $i;
#    if [ $selfballoon_enabled = "true" ]; then
      tgtkb=$(xenstore-read /local/domain/$i/memory/target);
      balloon_to_target $i $tgtkb;
#    fi;
  done;
  sleep $XENBALLOON_INTERVAL;
done


greetings
Viets


Dan Magenheimer wrote:
> Hi Viets --
> 
> A guest can't be ballooned without its "permission".
> The original implementation had the selfballooning
> in the guest's balloon driver, which could be rmmod'd
> inside the guest, so I don't think the old model
> was more secure than the new, which puts the selfballooning
> in a daemon.  The worst that a malicious guest can do in
> either case is ensure it always gets all the memory that's
> assigned to it.
> 
> Or have you thought of a different attack scenario?
> 
> Thanks for the testing.  Make sure you try running
> "watch -d xenballoond-monitor" in domain0.
> 
> Thanks,
> Dan
> 
>> -----Original Message-----
>> From: viets@xxxxxxx [mailto:viets@xxxxxxx]
>> Sent: Tuesday, July 01, 2008 6:06 AM
>> To: dan.magenheimer@xxxxxxxxxx
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: [Xen-devel] [PATCH] xenballoond (memory 
>> overcommit) scripts
>>
>>
>> Hello,
>>
>> is it a good idea to run a memory balloon process in a domU? 
>> As you know
>> I've tested your xenbus selfballooning, I've thought this 
>> make more sense?
>>
>> I thought it would be more secure and better for policing 
>> reasons to run
>> in dom0?
>>
>> I've just tested the script and it works fine, now i will try it for a
>> short periode...
>>
>> greetings
>> Viets
>>
>> Dan Magenheimer wrote:
>>> Attached is the current xenballoond script-set I
>>> talked about at Xen Summit 2008 that supports
>>> memory overcommit.
>>>
>>> I've had a number of requests for the scripts and,
>>> though more polishing would be nice, it makes sense
>>> to push them upstream so that others in the community
>>> can try/test them and improve on them.
>>>
>>> Note that there is no impact on any xen installation
>>> or on any guest unless the scripts are intentionally
>>> installed and configured on one or more guests.
>>>
>>> See the README and conf files for more info.
>>>
>>> All files are new so, in addition to the patch,
>>> these hg add commands will need to be done in
>>> the main tree.
>>>
>>> hg add tools/xenballoond
>>> hg add tools/xenballoond/xenballoond.init
>>> hg add tools/xenballoond/xenballoond
>>> hg add tools/xenballoond/xenballoon.conf
>>> hg add tools/xenballoond/xenballoon.README
>>> hg add tools/xenballoond/xenballoon-monitor
>>>
>>> Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
>>>
>>> Thanks,
>>> Dan
>>>
>>>
>>>
>> --------------------------------------------------------------
>> ----------
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> http://lists.xensource.com/xen-devel


-- 
Torben Viets                              w               Viets@xxxxxxx
n@work Internet Informationssysteme GmbH  o      http://support.work.de
Wandalenweg 5                             r   Tel.: +49 40 23 88 09 - 0
D-20097 Hamburg                           k   Fax:  +49 40 23 88 09 -29
HR B 61 668  - Amtsgericht Hamburg                    Gf Jan Diegelmann

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