Re: how to write paxctl MPROTECT-safe JIT code?

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

On Tue, Nov 15, 2016 at 01:55:16PM +0100, Thomas Klausner wrote:
> On Tue, Nov 15, 2016 at 01:42:56PM +0100, Joerg Sonnenberger wrote:
> > On Tue, Nov 15, 2016 at 12:34:14PM +0100, Thomas Klausner wrote:
> > > I've filed some upstream bug reports about paxctl issues, some existed
> > > already.
> > > 
> > > One developer asks how to fix the issue:
> > > 
> > > https://bugs.exim.org/show_bug.cgi?id=1749
> > > 
> > > Can someone please help out here?
> > 
> > The only safe and performant way I know is to create a temporary file,
> > unlink it and mmap it twice via the fd. It's a PITA.
> 
> So mkstemp() to get a file, unlink() to remove it, write the JIT code
> to the file. What are the two mmap()s for, what flags do they get?

One is writeable, the other is executable.

Joerg