Then it's extremely likely that Windows is bringing in the old memory
contents. Windows 10 really likes to hibernate instead of booting from
scratch. That probably explains the behavior you're seeing. I'm not
entirely sure how that can be prevented on the Windows side.
- Michal
On 7/31/2019 6:29 PM, b38911 Zxc wrote:
Hello Michal.
yes, good point. I did some tests and I obtained some mixed results, but
at the end, the behavior looks like:
- if I stop the boot at firmware and I dump the memory, no artefacts are
there
- if I continue the boot, sometimes artefacts appears in memory. So it
looks like it's a kind of caching of the operating system at this point.
It is not the "fast boot" option, which I already checked, so it's
probably something else. I need to dig on this.
Anyway, thanks for your help.
Il giorno mer 31 lug 2019 alle ore 16:01 Michal Necasek
<michal.neca...@oracle.com <mailto:michal.neca...@oracle.com>> ha scritto:
What does "shutdown the guest system/start again the guest system"
mean? Shut down the VM and start it again? Or reboot the guest OS
without terminating the VM?
In either case, I'd recommend dumping the VM's memory right after
the VM is reset (when it's executing firmware). Are the artifacts
there at that point?
Running with --dbg just shows the VM debugger UI, it does not
change the VM's behavior.
- Michal
----- Original Message -----
From: b38...@gmail.com <mailto:b38...@gmail.com>
To: michal.neca...@oracle.com <mailto:michal.neca...@oracle.com>
Sent: Tuesday, July 30, 2019 11:13:05 AM GMT +01:00 Amsterdam /
Berlin / Bern / Rome / Stockholm / Vienna
Subject: Re: [vbox-dev] Memory initialization
Hi Michal.
Sure, I'll try to explain better what I mean:
- start virtualbox and start a Windows 10 guest system (allocating
let's say 4GB of RAM)
- start a specific software in the guest, which, after its exits,
leave some artefacts in RAM (like a specific portion of code in
unallocated memory). So far, so good, nothing strange.
- shutdown the guest system
- start again the guest system
- looking into the RAM (dumping it), I still see the same artefacts,
even if I didn't ran the same software as before. Like if the
allocated RAM (still 4GB) was not re-initialized to 0
This make sense if the initial allocation does not set memory to 0
(or something else), since I'm not rebooting the host, so for sure
these artefacts are still in the host memory.
If you say that this is reset should be done, I'll try to re-run a
set of tests, may be I'm missing something. Consider that I'm
running the VM with --dbg option, not sure if this change something.
Thanks and let me know if you need more details on this.
Thanks
c
Il giorno mar 30 lug 2019 alle ore 10:11 Michal Necasek
<michal.neca...@oracle.com <mailto:michal.neca...@oracle.com>> ha
scritto:
Can you provide a simple reproduction scenario? What does one
have to
do to see this?
A VM reset should clear memory. A caveat is that a given
guest OS may
not perform a full reset but only a soft reboot, which does not
clear
memory.
- Michal
On 7/28/2019 10:15 PM, b38911 wrote:
> Hello all.
>
> I was suggested to post my question here.
>
> Here my doubt:
>
> I noticed this behavior, which is probably expected: dumping
the RAM of
> a guest (with ".pgmphystofile" command) I saw that the memory
is not
> initialized between virtual powercycle, like if there was a real
> powerdown. Sometimes, between restarts of the guest (with a
shutdown and
> then a restart), I find some memory artifacts belonging to
processes
> that shouldn't be there.
> I assume this happens because I'm not restarting the host
system, so
> probably the RAM is just remapped, but not initialized. This
is a bit
> annoying in some case, especially if you are using the system
for
> testing purposes.
>
> Is there a way to force the guest to initialize the allocated
RAM to
> zero (or something else), in order to emulate a real
powerdown-powerup?
> Thanks for your help.
>
> cips
>
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