Re: [Qemu-devel] [RFC] sanitize memory on system reset

[Peter Lieven]

On 13.06.2013 11:22, Andreas Färber wrote:
> Hi,
>
> Am 13.06.2013 08:09, schrieb Peter Lieven:
> > I was thinking if it would be a good idea to zeroize all memory
> > resources on system reset and
> > madvise dontneed them afterwards.
> The current way of not zeroing memory has led to discovery of some
> firmware bugs that we wouldn't have found if QEMU defaulted to zeroing.
The memory is zero at the start due to the use of mmap. Maybe
we need to add an option to add an initialization value anyway
because I am unsure if PERTURB works with mmap?!
> > This would avoid system reset attacks
> > in case the attacker
> > has only access to the console of a vServer but not on the physical host
> > and it would shrink
> > RSS size of the vServer siginificantly.
> Apart from the guest issue Stefan brought up (so far by definition we do
> a hard reset, so guests cannot assume soft reset semantics, but we
> should keep our options open), would not zeroing while marking pages as
> unused be an option? E.g., -reset-memory=DEADBEEF or some other
> command-line-specifiable pattern, absence would mean current behavior.
This would overwrite all contents with 0xdeadbeaf avoiding information
leak, but it would unnecessarily keep the memory alocated. So what
about an option -mem-sanitize with an optional parameter to write
a initialization value.

option missing -> no change
-mem-sanitize -> zeroize and madv_dontneed
-mem-sanitze=deadbeaf -> fill memory with 0xdeadbeaf

Where is the right postion to add this hook. qemu_system_reset() ?

Peter
> Regards,
> Andreas


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Mit freundlichen Grüßen

Peter Lieven

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