How can I change cr0 register in redhat system

How can I change cr0 register in redhat system

[Fan Yang]

hi all:
       when I change the cr0 register I get a "Segmentation fault (core
dumped)".
       my code is :


.data
.text
.global _start
_start:
        movl %eax, %cr0

      this code can work well in ubuntu system when I use root to run it.
So what can I do to work it in redhat system?

     thanks
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How can I change cr0 register in redhat system

[Ram Tummala]

On Jul 23, 2012, at 9:32 AM, Fan Yang <lljyangfan@gmail.com> wrote:

> hi all:
>        when I change the cr0 register I get a "Segmentation fault (core dumped)".
>        my code is :
>
>
> .data
> .text
> .global _start
> _start:
>         movl %eax, %cr0
>
>       this code can work well in ubuntu system when I use root to run it. So what can I do to work it in redhat system?
Changing a control register is a privileged operation. You can't do it
from the user space. You can only do it from ring 0.

Venkatram Tummala
>
>      thanks
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

How can I change cr0 register in redhat system

[siddharth saxena]

Hi all

I have a certain configuration file which includes other files.
Lets say
*#include<asm/arch/fileabc.h>*

Now under directory
*include/asm/*

I'm not having any directory as *arch*, instead it is *arch-omap4* and so I
also have a link *arch - > arch-omap4*

but when I'm building the code, there is error :
*fatal error: asm/arch/fileabc.h : No such file or directory*
*
*
*Any problem with the link ?*
*
*
*
*
Regards
Siddharth
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How can I change cr0 register in redhat system

[Jonathan Neuschäfer]

On Mon, Jul 23, 2012 at 02:07:41PM +0530, siddharth saxena wrote:
> Hi all
> 
> I have a certain configuration file which includes other files.
> Lets say
> *#include<asm/arch/fileabc.h>*

Where is your "configuration file" located?
Is it fileabc.h, or does it include fileabc.h?

> Now under directory
> *include/asm/*

I don't have include/asm/ in my copy of the linux source code (v3.5-rc4),
did you add it yourself?

> I'm not having any directory as *arch*, instead it is *arch-omap4* and so I
> also have a link *arch - > arch-omap4*

The thing that looks the most like what you seem to be trying to do is
arch/arm/mach-*

> but when I'm building the code, there is error :
> *fatal error: asm/arch/fileabc.h : No such file or directory*
> *
> *
> *Any problem with the link ?*

Which link?
If you mean the linker or the linking proccess, then no: It doesn't get
that far.


HTH,
	Jonathan Neusch?fer

PS: Please don't reply to emails on the mailing list if you're starting
    a new discussion.

How can I change cr0 register in redhat system

[Fan Yang]

2012/7/23 Ram Tummala <venkatram867@gmail.com>

> On Jul 23, 2012, at 9:32 AM, Fan Yang <lljyangfan@gmail.com> wrote:
>
> > hi all:
> >        when I change the cr0 register I get a "Segmentation fault (core
> dumped)".
> >        my code is :
> >
> >
> > .data
> > .text
> > .global _start
> > _start:
> >         movl %eax, %cr0
> >
> >       this code can work well in ubuntu system when I use root to run
> it. So what can I do to work it in redhat system?
>
> Changing a control register is a privileged operation. You can't do it
> from the user space. You can only do it from ring 0.
>
> Venkatram Tummala
> >
> >      thanks
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
May be I can work it by adding a new syscall in the kernel, right?
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How can I change cr0 register in redhat system

[Jonathan Neuschäfer]

On Mon, Jul 23, 2012 at 09:38:44PM +0800, Fan Yang wrote:
> May be I can work it by adding a new syscall in the kernel, right?

A sysfs-based interface should do it just as well.


Jonathan Neusch?fer

How can I change cr0 register in redhat system

[Ram Tummala]

On Jul 23, 2012, at 7:08 PM, Fan Yang <lljyangfan@gmail.com> wrote:



2012/7/23 Ram Tummala <venkatram867@gmail.com>

> On Jul 23, 2012, at 9:32 AM, Fan Yang <lljyangfan@gmail.com> wrote:
>
> > hi all:
> >        when I change the cr0 register I get a "Segmentation fault (core
> dumped)".
> >        my code is :
> >
> >
> > .data
> > .text
> > .global _start
> > _start:
> >         movl %eax, %cr0
> >
> >       this code can work well in ubuntu system when I use root to run
> it. So what can I do to work it in redhat system?
>
> Changing a control register is a privileged operation. You can't do it
> from the user space. You can only do it from ring 0.
>
> Venkatram Tummala
> >
> >      thanks
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
May be I can work it by adding a new syscall in the kernel, right?

Yes you can add a syscall in the kernel or can use procfs or sysfs but you
should fully understand the consequences. The code will never be accepted
by the kernel community. Exporting such functionality to the user space is
recipe for disaster. It would open up a simple DOS attack and that is just
a start.

Hardware Control registers are just not supposed to be handled by the user
space.

Venkatram Tummala
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How can I change cr0 register in redhat system

[Peter Teoh]

u have to put the asm code in kernel module, and load it via "insmod" and
when it execute, it will affect all the processes .....and btw, your
version is dangerous....normally people will always query the latest value
of Cr0, and then OR with the value they want to modify.   below is one that
worked:

http://stackoverflow.com/questions/3962950/how-to-set-control-register-0-cr0-bits-in-x86-64-using-gcc-assembly-on-linux


On Mon, Jul 23, 2012 at 12:00 PM, Fan Yang <lljyangfan@gmail.com> wrote:

> hi all:
>        when I change the cr0 register I get a "Segmentation fault (core
> dumped)".
>        my code is :
>
>
> .data
> .text
> .global _start
> _start:
>         movl %eax, %cr0
>
>       this code can work well in ubuntu system when I use root to run it.
> So what can I do to work it in redhat system?
>
>      thanks
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>


-- 
Regards,
Peter Teoh
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