linux-kernel - Re: [S390] mm: add devmem_is_allowed() for STRICT

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Message-ID: <20101117180320.GA13441@redhat.com>
Date:	Wed, 17 Nov 2010 13:03:21 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com
Subject: Re: [S390] mm: add devmem_is_allowed() for STRICT_DEVMEM checking

On Tue, Nov 16, 2010 at 11:59:03PM +0000, Linux Kernel wrote:
 > Gitweb:     http://git.kernel.org/linus/ec6743bb06510c7b629603ce35713d6ae9273579
 > Commit:     ec6743bb06510c7b629603ce35713d6ae9273579
 > Parent:     ca768b663131ca644689fcadc9ca092dcc96a758
 > Author:     Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
 > AuthorDate: Wed Nov 10 10:05:55 2010 +0100
 > Committer:  Martin Schwidefsky <sky@...hwide.boeblingen.de.ibm.com>
 > CommitDate: Wed Nov 10 10:05:54 2010 +0100
 > 
 >     [S390] mm: add devmem_is_allowed() for STRICT_DEVMEM checking
 >     
 >     Provide the devmem_is_allowed() routine to restrict access to
 >     kernel memory from userspace.
 >     Set the CONFIG_STRICT_DEVMEM config option to switch on checking.
 >     
 >     Signed-off-by: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
 >     Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>

[snip add kconfig]

...

 > +static inline int devmem_is_allowed(unsigned long pfn)
 > +{
 > +	return 0;
 > +}

So you add the config option that promises security, but then you always
allow the access.  This seems pointless ?  Why bother having the option at all?

	Dave

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