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Re: zero filling pages

On Tuesday, July 22, 2003, at 20:39, Nat! wrote:

Probably a FAQ, but OK anyway :)

Whenever I allocate memory with vm_allocate I get a zero filled paged. AFAIK I can't get around this for security reasons, the reason being that another process should not look into another processes memory space, to glean some information.

OK two questions:

Is there really no (reasonable easy) way to get around this ?

AFAIK, no. There is no reasonable way to get around this.


Zero filling is my bottleneck currently.

Are you sure? how did you determine this.

I can see the rationale on a multi-user, time sharing system (AKA as the bad old days), but on a single-user machine like Mac OS X I would not deem it important enough. (Mac OS X Server maybe, but Mac OS X Client ?)

MacOSX/Darwin *is* a multi-user operating system (as are all UNIX-like operating systems). Besides, zero-filling pages is a good idea even on a single user system. Take the following situation:

A single process on your machine is exploited, and is now running malicious code. Without zero-filled pages, this process could just repeatedly call vm_allocate and examine the unallocated pages on your system. It could then, search for recognizable patterns in the pages (credit card numbers, addresses, social security numbers, etc.).



--
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Clark S. Cox, III
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 >zero filling pages (From: Nat! <email@hidden>)



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