Re: machine independent protection from stack-smashing attack

[Jan Echternach <echter () informatik uni-rostock de>]

On Mon, Sep 11, 2000 at 09:55:35AM +0400, Yarrow Charnot wrote:
> > > Microsoft purposely doesn't allow pages to be non-executable,

Microsoft didn't really have a choice.  i386 hardware doesn't support
readable, but non-executable pages.

> In other words, if the attribute READ is set, the page is automatically made
> EXECUTABLE. If you trace NT and 9X kernels up to the point where they set

Same with Linux/i386, for instance.

> (NON-EXECUTABLE) on purpose. What purpose? Who on Earth would want to keep
> your data segments executable??? If you want to make it executable, one call

Segment based protections on i386 are different thing.  I think you
could emulate a flat memory model with non-executable pages by mapping
data and code segments to different linear addresses, but that would
half the availabe virtual memory and impose a performance penalty.

--
Jan