[TALK] Proving fundamental Unix guarantees

Chris Maltby chris at sw.oz.au
Mon Jun 30 17:49:58 EST 2003

On Mon, Jun 30, 2003 at 03:01:09PM +0800, Grahame Bowland wrote:
> Zeroing pages handed back from an application to the operating system
> isn't something generally done. Apparently OpenBSD does do it, and
> FreeBSD zeroes pages when there is system idle time.

I wonder which pages OpenBSD clears on de-reference? Presumably when
it's the last reference to an anonymous page. I wonder if they also
clear any associated swap space?

> Linux has been known to leak information through ICMP echo replies,
> so I doubt it does zeroing on pages!

ICMP echo replies are generated in the kernel. What Linux (or other 
OSs) might leak is the contents of old packet buffers.

> Paranoid applications should zero it themselves, and investigate the
> various syscalls to prevent pages being swapped out to disk, although
> that usually needs superuser privileges.

I'm not sure what problem your "paranoid" application would be trying
to avoid by this means...


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