Executing from readablee, no-exec pages

[Benjamin Herrenschmidt]

On Fri, 2007-07-06 at 10:42 -0400, David Woodhouse wrote:
> On Thu, 2007-07-05 at 16:55 -0500, Scott Wood wrote:
> > To maintain compatibility with these versions, we could change the test 
> > in do_page_fault() to include VM_READ as well as VM_EXEC on targets that 
> > don't have a separate exec-bit in hardware (are there any powerpc mmus 
> > that do?).  
> 
> 64-bit implementations since POWER4 have separate exec permissions,
> don't they? So any userspace which tries to execute non-executable pages
> is already broken when running on a ppc64 machine; I wouldn't worry too
> much about letting it break on ppc32 too.
> 
> We already use vDSO signal trampolines even on the 32-bit kernel, right?

The problem was with old glibc 32 bits which used to jump to an
instruction in the .got iirc that wasn't in an executable section

Ben.