Xen devel - Jun 2006 - how to disable the NX flag in a domU?

Hi,

I am having problems with an unclean written closed source application, which
segfaults by time, because it has executable code on the stack.

Is it possible, to disable the NX bit on modern processors for a domU? I know,
this is an unclean solution - but it would be a quick fix.

Many thanks in advance,

Johnny

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On 28 Jun 2006, at 10:15, Hans-Christian Armingeon wrote:
> I am having problems with an unclean written closed source 
> application, which segfaults by time, because it has executable code 
> on the stack.
>
> Is it possible, to disable the NX bit on modern processors for a domU? 
> I know, this is an unclean solution - but it would be a quick fix.
You can specify ''noexec=off'' to your domU Linux.

  -- Keir


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Pass "noexec=off" to the kernel, and it won''t set the NX bit
in it''s
page-table entries, and I presume Xen will just use the same bits as the
guest asks for... One would think, at least.. [I haven''t tried this, I
just scanned the kernel source code for the boot-line argument, as I
knew there is some way to enable/disable it...]

Care to divulge what the app is so I can add it to the list of apps that
I''m not going to use? ;-)

--
Mats
> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com 
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
> Hans-Christian Armingeon
> Sent: 28 June 2006 10:16
> To: xen-devel@lists.xensource.com
> Subject: [Xen-devel] how to disable the NX flag in a domU?
> 
> Hi,
> 
> I am having problems with an unclean written closed source 
> application, which segfaults by time, because it has 
> executable code on the stack.
> 
> Is it possible, to disable the NX bit on modern processors 
> for a domU? I know, this is an unclean solution - but it 
> would be a quick fix.
> 
> Many thanks in advance,
> 
> Johnny
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
> 


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Hi,

Am Mittwoch, 28. Juni 2006 12:39 schrieb Keir Fraser:
> 
> On 28 Jun 2006, at 10:15, Hans-Christian Armingeon wrote:
> 
> > I am having problems with an unclean written closed source 
> > application, which segfaults by time, because it has executable code 
> > on the stack.
> >
> > Is it possible, to disable the NX bit on modern processors for a domU?
> > I know, this is an unclean solution - but it would be a quick fix.
> 
> You can specify ''noexec=off'' to your domU Linux.
I have

extra = "noexec=off"

in my domU config, but I still get segfaults. I wrote a small program, that
executes a printf on the stack, and it doesn''t work. It works fine on
x86 - it executes the printf on the stack.

Do I need to disable the nx flag globally on dom0?

Johnny
> 
>   -- Keir
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
_______________________________________________
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Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

Hi,

Am Mittwoch, 28. Juni 2006 12:39 schrieb Keir Fraser:
> 
> On 28 Jun 2006, at 10:15, Hans-Christian Armingeon wrote:
> 
> > I am having problems with an unclean written closed source 
> > application, which segfaults by time, because it has executable code 
> > on the stack.
> >
> > Is it possible, to disable the NX bit on modern processors for a domU?
> > I know, this is an unclean solution - but it would be a quick fix.
> 
> You can specify ''noexec=off'' to your domU Linux.
I have

extra = "noexec=off"

in my domU config, but I still get segfaults. I wrote a small program, that
executes a printf on the stack, and it doesn''t work. It works fine on
x86 - it executes the printf on the stack.

Do I need to disable the nx flag globally on dom0?

Johnny
> 
>   -- Keir
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
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