Re: PAX mprotect and JIT

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Sun, Feb 26, 2017 at 10:30:05AM +0100, Martin Husemann wrote:
> > (2) A hack for allow mprotect to switch between W and X, but still
> > honoring W^X. This is a hack and needs to be carefully rethought,
> > since I believe the way pax is currently implemented is wrong. Consider
> > it a PoC.
> 
> Wouldn't it be better to create a variant of mremap() that allows
> specifying the new protection flags and only allow a W^X toggle in
> the M_REMAPDUP case?

The mremap() dance is only desirable for multi-threaded JIT. If you
compile a module at a time before making it visible, just a plain
mprotect is enough.

Joerg