Re: [PATCH v3 2.6.39-rc1-tip 12/26] 12: uprobes: slot allocation for uprobes

[Eric Paris <eparis@redhat.com>]

On Thu, 2011-04-21 at 19:41 +0530, Srikar Dronamraju wrote:
> * Eric Paris <eparis@parisplace.org> [2011-04-20 09:40:57]:

> > Now how to fix the problems you were seeing.  If you run a modern
> > system with a GUI I'm willing to bet the pop-up window told you
> > exactly how to fix your problem.  If you are not on a GUI I accept
> > it's a more difficult as you most likely don't have the setroubleshoot
> > tools installed to help you out.  I'm just guess what your problem
> > was, but I think you have two solutions either:
> 
> I am not running GUI on my testbox and mostly disable selinux unless I
> need to test if uprobes works on selinux environment.
> 
> > 
> > 1) chcon -t unconfined_execmem_t /path/to/your/binary
> > 2) setsebool -P allow_execmem 1
> > 
> > The first will cause the binary to execute in a domain with
> > permissions to execute anonymous memory, the second will allow all
> > unconfined domains to execute anonymous memory.
> 
> We arent restricted to a particular binary/binaries. We want an
> infrastructure that can trace all user-space applications. So the
> first option doesnt seem to help us.
> 
> If I understand the second option. we would want this command to be
> run on any selinux enabled machines that wants uprobes to be working.

The check which I'm guessing you ran into problems is done using the
permissions of the 'current' task.  I don't know how your code works at
all, but I would have guessed that the task allocating and adding this
magic page was either perf or systemtap or something like that.  Not the
'victim' task where the page would actually show up.  Is that true?  If
so, method1 (or 2) works.  If not, and 'current' is actually the victim,
method2 would work some of the time, but not always.

If current can be the victim (or some completely random task) we can
probably switch the credentials of the current task as we do the
allocation to the initial creds (or something like that) so the
permission will be granted.

Unrelated note: I'd prefer to see that page be READ+EXEC only once it
has been mapped into the victim task.  Obviously the portion of the code
that creates this page and sets up the instructions to run is going to
need write.  Maybe this isn't feasible.  Maybe this magic pages gets
written a lot even after it's been mapped in.  But I'd rather, if
possible, know that my victim tasks didn't have a WRITE+EXEC page
available......

-Eric