linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.

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Message-ID: <20110127102527.GT19725@linux.vnet.ibm.com>
Date:	Thu, 27 Jan 2011 15:55:27 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20]  5: Uprobes:
 register/unregister probes.

* Peter Zijlstra <peterz@...radead.org> [2011-01-27 11:23:37]:

> On Thu, 2011-01-27 at 15:31 +0530, Srikar Dronamraju wrote:
> > > > >  - validate that the vma is indeed a map of the right inode
> > > > 
> > > > We can add a check in write_opcode( we need to pass the inode to
> > > > write_opcode).
> > > 
> > > sure..
> > > 
> > > > >  - validate that the offset of the probe corresponds with the stored
> > > > > address
> > > > 
> > > > I am not clear on this. We would have derived the address from the
> > > > offset. So is that we check for
> > > >  (vaddr == vma->vm_start + uprobe->offset)
> > > 
> > > Sure, but the vma might have changed since you computed the offset -)
> > 
> > If the vma has changed then it would fail the 2nd validation i.e vma
> > corresponds to the uprobe inode right. If the vma was unmapped and
> > mapped back at the same place, then I guess we are okay to probe.
> 
> It can be unmapped and mapped back slightly different. A map of the same
> file doesn't need to mean its in the exact same location or has the
> exact same pgoffset.
> 
> 

If its not at the exact same location, then our third validation of
checking that (vaddr == vma->vm_start + uprobe->offset)  should fail
right?

Also should it be (vaddr == uprobe->offset + vma->vm_start -
vma->pgoff << PAGE_SHIFT) ?

-- 
Thanks and Regards
Srikar
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