Re: UVM and the NULL page

[David Holland <dholland-tech%netbsd.org@localhost>]

On Mon, Dec 26, 2016 at 04:40:16PM -0500, Mouse wrote:
 > > The only reason I know for mapping address zero [...]
 > 
 > > Anyway mmap() without MAP_FIXED should never return NULL.
 > 
 > Perhaps it's time to implement null pointers as something other than
 > all-bits-zero?

Wouldn't help much; the next obvious (probably only viable) candidate
is all-bits-1 and then you just need a slightly larger offset from it
to jump to userspace.

Userspace memory shouldn't have supervisor execute permission anyway,
although I suppose x86 can't represent that.

-- 
David A. Holland
dholland%netbsd.org@localhost