memory pages nulling when releasing

[Chuck Swiger]

Nick Borisov wrote:
> Could you tell me if FreeBSD supports memory page nulling when
> releasing it to prevent unauthorized access to data left in the page
> after it's allocated again.

Yes, FreeBSD has a mechanism for "zero-filling" used pages before they are 
allocated to another process, although this is normally deferred for a while 
to promote reuse of the page if the original process needs to use it again.

> If it does, what sys calls etc provide that?
> IMHO this is an important issue when operating data with different
> sensivity levels.

You can set some malloc() tunables to control some of this, although if you 
are trying to do secure programming of sensitive data, look towards mlock() to 
keep the data resident and unpageable to keep it out of the VM system and 
potentially the swapfile.

Look at the source for GnuPG, for example, or OPIE...

-- 
-Chuck