non-executable stack

[Peter Wemm]

On Tuesday 14 December 2004 11:00 am, Sean McNeil wrote:
> Just wondering if FreeBSD is taking advantage of the non-execute
> capability in the amd64 processor to protect the stack and allocation
> area.  If so, how would something like the java VM work?  Would it
> have to have some sort of chflag bit set or suid'd?
>
> Cheers,
> Sean

We sort-of support the PG_NX bit, but there are things broken in the 
pmap.c code which means it will get lost over time.

We cheat and create the primary stack with execute turned on, because 
the executable signal trampoline is still in there.  The signal 
trampoline should be in libc anyway.

gcc needs to have its configuration changed so that it uses mprotect() 
to turn PROT_EXEC on when it needs to execute stuff on the stack.  It 
does this for many architectures, but not for FreeBSD/i386 and /amd64.

Things like the java vm would need to use mprotect() like they do on 
solaris, linux etc.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5