linux-kernel - Re: Undoing module RONX protection

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Message-ID: <874o5v6drb.fsf@rustcorp.com.au>
Date:	Mon, 18 Apr 2011 20:13:36 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christoph Hellwig <hch@...radead.org>,
	Jan Glauber <jang@...ux.vnet.ibm.com>
Cc:	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

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.

Might have been nicer as three separate patches, in future.

Thanks!
Rusty.
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