Fwd: Need Help regarding Reading and Writting to a file from kernel function file

Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Sahibzada Irfanullah]

[-- Attachment #1.1: Type: text/plain, Size: 1164 bytes --]

Dear Sir,
Hope you are doing well. Actually, I have one problem metioned in the
subject line. The problem is:  I am trying to write/read page faulted
physical addresses to a file in a kernel (v5.3-1) function, i.e.,
handle_ept_violation() which is present in vmx.c. I have followed this
<https://stackoverflow.com/questions/1184274/read-write-files-within-a-linux-kernel-module>,
it's working as a standalone kernel module when I load/unload this kernel
module, but when I try to use this code in the handle_ept_violation()
function, I can't able to open the file and get the error codes, i.e., -2,
-3, or -13. It's compiled successfully but generate the error at runtime. I
searched for error codes online but I didn't find any help.
Can anyone please provide me with any good guidlines, or links where I can
start and solve this problem in a fast way.
Thank you very much

-- 
Regards,

*Mr. Irfan Ullah*
PhD Candidate
Data and Knowledge Engineering(DKE) Lab
Department of Computer Science and Engineering
Kyung Hee University, South Korea.
 +82-010-591-51651 <+82%2010-3877-8867>
  sahibzada.iu@gmail.com
 sahibzada_irfanullah



-- 
Regards,

*Mr. Irfanullah*

[-- Attachment #1.2: Type: text/html, Size: 4584 bytes --]

[-- Attachment #2: Type: text/plain, Size: 170 bytes --]

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Greg KH]

On Tue, Sep 24, 2019 at 04:10:07PM +0900, Sahibzada Irfanullah wrote:
> Dear Sir,
> Hope you are doing well. Actually, I have one problem metioned in the
> subject line. The problem is:  I am trying to write/read page faulted
> physical addresses to a file in a kernel (v5.3-1) function, i.e.,
> handle_ept_violation() which is present in vmx.c. I have followed this
> <https://stackoverflow.com/questions/1184274/read-write-files-within-a-linux-kernel-module>,
> it's working as a standalone kernel module when I load/unload this kernel
> module, but when I try to use this code in the handle_ept_violation()
> function, I can't able to open the file and get the error codes, i.e., -2,
> -3, or -13. It's compiled successfully but generate the error at runtime. I
> searched for error codes online but I didn't find any help.
> Can anyone please provide me with any good guidlines, or links where I can
> start and solve this problem in a fast way.

Please do not try to read or write a file from within the kernel, that
way almost always lies madness and major problems.

Step back and try to describe the problem you are attempting to solve
here first.  Odds are it can be done in a much better way.

Also, do you have a pointer to your code anywhere?

thanks,

greg k-h

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Valdis Klētnieks]

[-- Attachment #1.1: Type: text/plain, Size: 1026 bytes --]

On Tue, 24 Sep 2019 16:10:07 +0900, Sahibzada Irfanullah said:

> subject line. The problem is:  I am trying to write/read page faulted
> physical addresses to a file in a kernel (v5.3-1) function, i.e.,
> handle_ept_violation() which is present in vmx.c. I have followed this
> <https://stackoverflow.com/questions/1184274/read-write-files-within-a-linux-kernel-module>,

Just because somebody on stackoverflow gave a guide doesn't mean it's
a good idea.

What problem are you trying to solve here?  Are you trying to write the faulted
pages themselves to a file?  In that case, just creating the file, using something like
'dd if=/dev/zero of=/your/file/here bs=1M count=4096' and then using mkswap
and swapon will probably work much better.

If you're trying to produce a trace of what pages are being faulted, you can
probably do a better job by using 'perf' to produce trace events with a lot of
added data for you, or use debugfs or netlink and a userspace program to read
the data and write it to disk from userspace.


[-- Attachment #1.2: Type: application/pgp-signature, Size: 832 bytes --]

[-- Attachment #2: Type: text/plain, Size: 170 bytes --]

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Saket Sinha]

Hi,

I am sorry but I am really tempted to share -
https://www.linuxjournal.com/article/8110

But as suggested, you should never try this.

Regards,
Saket Sinha

On Tue, Sep 24, 2019 at 10:50 AM Valdis Klētnieks
<valdis.kletnieks@vt.edu> wrote:
>
> On Tue, 24 Sep 2019 16:10:07 +0900, Sahibzada Irfanullah said:
>
> > subject line. The problem is:  I am trying to write/read page faulted
> > physical addresses to a file in a kernel (v5.3-1) function, i.e.,
> > handle_ept_violation() which is present in vmx.c. I have followed this
> > <https://stackoverflow.com/questions/1184274/read-write-files-within-a-linux-kernel-module>,
>
> Just because somebody on stackoverflow gave a guide doesn't mean it's
> a good idea.
>
> What problem are you trying to solve here?  Are you trying to write the faulted
> pages themselves to a file?  In that case, just creating the file, using something like
> 'dd if=/dev/zero of=/your/file/here bs=1M count=4096' and then using mkswap
> and swapon will probably work much better.
>
> If you're trying to produce a trace of what pages are being faulted, you can
> probably do a better job by using 'perf' to produce trace events with a lot of
> added data for you, or use debugfs or netlink and a userspace program to read
> the data and write it to disk from userspace.
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Martin Christian]

[-- Attachment #1.1.1: Type: text/plain, Size: 822 bytes --]

> Just because somebody on stackoverflow gave a guide doesn't mean it's
> a good idea.

I'll put that on my quotation list. ;-)

Regards,

Martin

-- 
Dipl.-Inf. Martin Christian
Senior Berater Entwicklung Hardware
Division Verteidigung
secunet Security Networks AG

Tel.: +49 201 5454-3612, Fax +49 201 5454-1323
E-Mail: martin.christian@secunet.com
Ammonstraße 74, 01067 Dresden
www.secunet.com
__________________________________________________________________________

secunet Security Networks AG
Sitz: Kurfürstenstraße 58, 45138 Essen, Deutschland
Amtsgericht Essen
HRB 13615
Vorstand: Axel Deininger (Vors.), Torsten Henn, Dr. Kai Martius,
          Thomas Pleines
Aufsichtsratsvorsitzender: Ralf Wintergerst
__________________________________________________________________________


[-- Attachment #1.2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[-- Attachment #2: Type: text/plain, Size: 170 bytes --]

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Fwd: Need Help regarding Reading and Writting to a file from kernel function file

[Greg KH]

On Tue, Sep 24, 2019 at 11:51:57AM +0200, Saket Sinha wrote:
> Hi,
> 
> I am sorry but I am really tempted to share -
> https://www.linuxjournal.com/article/8110

That's out of date, and the stack overflow link points to it.

Maybe someday I'll update that article somewhere else, as it's actually
much simpler to do this now than it was when I wrote that article.  But
it still doesn't make it something that anyone should do :)

thanks,

greg k-h

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies