linux-kernel - Re: Undoing module RONX protection fix

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Date:	Wed, 27 Apr 2011 14:42:34 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jan Glauber <jang@...ux.vnet.ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, castet.matthieu@...e.fr,
	sliakh.lkml@...il.com, jiang@...ncsu.edu, mingo@...e.hu
Subject: Re: Undoing module RONX protection fix

On Thu, 21 Apr 2011 16:19:49 +0200, Jan Glauber <jang@...ux.vnet.ibm.com> wrote:
> On Mon, Apr 18, 2011 at 08:13:36PM +0930, Rusty Russell wrote:
> > On Mon, 18 Apr 2011 11:23:48 +0200, Jan Glauber <jang@...ux.vnet.ibm.com> wrote:
> > > While debugging I stumbled over two problems in the code that protects module
> > > pages.
> > > 
> > > First issue is that disabling the protection before freeing init or unload of
> > > a module is not symmetric with the enablement. For instance, if pages are set
> > > to RO the page range from module_core to module_core + core_ro_size is
> > > protected. If a module is unloaded the page range from module_core to
> > > module_core + core_size is set back to RW.
> > > So pages that were not set to RO are also changed to RW.
> > > This is not critical but IMHO it should be symmetric.
> > > 
> > > Second issue is that while set_memory_rw & set_memory_ro are used for
> > > RO/RW changes only set_memory_nx is involved for NX/X. One would await that
> > > the inverse function is called when the NX protection should be removed,
> > > which is not the case here, unless I'm missing something.
> > > 
> > > The following patch addresses both issues. Works on s390. Boot tested on x86.
> > > 
> > > Please comment,
> > 
> > Applied, minus the S/390 EXPORT_SYMBOL which Christoph pointed out.  I
> > turned your mail into the commit message, since it was clearer and more
> > verbose.  I don't see why they would be different.
> 
> There's a bug in my patch which just killed one of my s390 machines.
> Can you merge this with the previuos patch?

Hmm...

Applied, but that function is really kind of silly.  We should probably
just split into unset_section_ro_nx() into unset_module_init_ro_nx() and
unset_module_core_ro_nx().

(And why isn't that function static anyway?)

Patch appreciated :)
Rusty.
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