breakpoint assistance: single-step out of line

[Jim Keniston]

On Fri, 2007-03-16 at 10:09 -0400, Frank Ch. Eigler wrote:
> Roland McGrath <roland@redhat.com> writes:
> 
> > The method of single-stepping over an out of line copy of the
> > instruction clobbered by breakpoint insertion has been proven by
> > kprobes.  The complexities are mitigated in that implementation by
> > the constrained context of the kernel and the fixed subset of
> > possible machine code known to validly occur in any kernel or module
> > text.
> 
> Another important aspect is that userspace may be hostile.  Beyond
> just containing oddball instruction sequences, it may deliberately
> rewrite its own .text, or otherwise interfere with probing in order to
> produce crashes or security breaches.

Under what circumstances can a user program rewrite its own text?

> 
> - FChE

Jim