Problems with hypercalls

Problems with hypercalls

[emilie lefebvre]

 Hi all,

I try to do hypercalls but I always have a kernel panic that I don't understand.
I have Scentific Linux 6 installed on  kvm and my computer has ubuntu.
I try to modify the SL6 kernel to do hypercalls.
I have a function in that kernel which check all syscalls in the VM.

When I put the hypercall at the beginning of this function, it perfectly works,
but when I try to put it in the middle of the function I have a kernel panic with this
error:

"divide error: 0000 [#1] SMP 
...
 [<ffffffff813f8cdd>] panic+0x78/0x137
 [<ffffffff813fcb94>] oops_end+0xe4/0x100
 [<ffffffff8101021b>] die+0x5b/0x90
 [<ffffffff813fc444>] do_trap+0xc4/0x160
 [<ffffffff8100df2f>] do_divide_error+0x8f/0xb0
 [<ffffffff811f974c>] ? my_function+0xdc/0xe70 "

Could you have any suggestions ?

With regards,
Emilie

 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110607/01e508ed/attachment.html 

Problems with hypercalls

[Mulyadi Santosa]

On Tue, Jun 7, 2011 at 15:39, emilie lefebvre <tricheurs@hotmail.fr> wrote:
> "divide error: 0000 [#1] SMP
> ...
> ?[<ffffffff813f8cdd>] panic+0x78/0x137
> ?[<ffffffff813fcb94>] oops_end+0xe4/0x100
> ?[<ffffffff8101021b>] die+0x5b/0x90
> ?[<ffffffff813fc444>] do_trap+0xc4/0x160
> ?[<ffffffff8100df2f>] do_divide_error+0x8f/0xb0
> ?[<ffffffff811f974c>] ? my_function+0xdc/0xe70 "
>
> Could you have any suggestions ?

Could you show us your code? perhaps by pasting them somewhere?

>From what I guess, sounds like your code did some math (directly or
indirectly) that fiddle with floating point numbers?


-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

Problems with hypercalls

[Rajat Sharma]

are you doing 64bit devision on 32 bit arch? If that is the case,
do_div is worth considering.

On Wed, Jun 8, 2011 at 3:25 PM, Mulyadi Santosa
<mulyadi.santosa@gmail.com> wrote:
> On Tue, Jun 7, 2011 at 15:39, emilie lefebvre <tricheurs@hotmail.fr> wrote:
>> "divide error: 0000 [#1] SMP
>> ...
>> ?[<ffffffff813f8cdd>] panic+0x78/0x137
>> ?[<ffffffff813fcb94>] oops_end+0xe4/0x100
>> ?[<ffffffff8101021b>] die+0x5b/0x90
>> ?[<ffffffff813fc444>] do_trap+0xc4/0x160
>> ?[<ffffffff8100df2f>] do_divide_error+0x8f/0xb0
>> ?[<ffffffff811f974c>] ? my_function+0xdc/0xe70 "
>>
>> Could you have any suggestions ?
>
> Could you show us your code? perhaps by pasting them somewhere?
>
> >From what I guess, sounds like your code did some math (directly or
> indirectly) that fiddle with floating point numbers?
>
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

Problems with hypercalls

[emilie lefebvre]

This is my function :


static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;

static int piga_seq_cpt = 1;

/*
* Function called for each systemcall (Hook SELinux avc function)
*/
int piga_control(u32 ssid, ...., struct av_decision * avd) {

/*
* Here my hypercall work but block my vm with this error :

*                " BUG: scheduling while atomic ... "
*/

spin_lock_bh(&xgr_learn_lock);

  if ( in_atomic())

           kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned long)piga_seq_cpt);

  spin_unlock_bh(&xgr_learn_lock);   

    

 if (piga_on == 1) {

/*
* Here my hypercall make a kernel panic with this error:
*             " divide error: 0000 [#1] SMP"
*/
                spin_lock_bh(&xgr_learn_lock);

                set_current_state(TASK_UNINTERRUPTIBLE);

                kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned long)piga_seq_cpt);

                set_current_state(TASK_RUNNING);

                spin_lock_bh(&xgr_learn_lock);

}

}

 
 




> Date: Wed, 8 Jun 2011 15:52:33 +0530
> Subject: Re: Problems with hypercalls
> From: fs.rajat at gmail.com
> To: mulyadi.santosa at gmail.com
> CC: tricheurs at hotmail.fr; kernelnewbies at kernelnewbies.org
> 
> are you doing 64bit devision on 32 bit arch? If that is the case,
> do_div is worth considering.
> 
> On Wed, Jun 8, 2011 at 3:25 PM, Mulyadi Santosa
> <mulyadi.santosa@gmail.com> wrote:
> > On Tue, Jun 7, 2011 at 15:39, emilie lefebvre <tricheurs@hotmail.fr> wrote:
> >> "divide error: 0000 [#1] SMP
> >> ...
> >>  [<ffffffff813f8cdd>] panic+0x78/0x137
> >>  [<ffffffff813fcb94>] oops_end+0xe4/0x100
> >>  [<ffffffff8101021b>] die+0x5b/0x90
> >>  [<ffffffff813fc444>] do_trap+0xc4/0x160
> >>  [<ffffffff8100df2f>] do_divide_error+0x8f/0xb0
> >>  [<ffffffff811f974c>] ? my_function+0xdc/0xe70 "
> >>
> >> Could you have any suggestions ?
> >
> > Could you show us your code? perhaps by pasting them somewhere?
> >
> > >From what I guess, sounds like your code did some math (directly or
> > indirectly) that fiddle with floating point numbers?
> >
> >
> > --
> > regards,
> >
> > Mulyadi Santosa
> > Freelance Linux trainer and consultant
> >
> > blog: the-hydra.blogspot.com
> > training: mulyaditraining.blogspot.com
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110608/f040c726/attachment.html 

Problems with hypercalls

[Mulyadi Santosa]

Hi...

On Wed, Jun 8, 2011 at 21:54, emilie lefebvre <tricheurs@hotmail.fr> wrote:
>
> This is my function :
>
> static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;
> static int piga_seq_cpt = 1;
>
> /*
> * Function called for each systemcall (Hook SELinux avc function)
> */
> int piga_control(u32 ssid, ...., struct av_decision * avd) {
>
> /*
> * Here my hypercall work but block my vm with this error :
> * ?????????????? " BUG: scheduling while atomic ... "
> */
>
> spin_lock_bh(&xgr_learn_lock);
> ? if ( in_atomic())
> ?????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> long)piga_seq_cpt);

AFAIK, anything that trigger context switching, usually trigger
rescheduling too....or in other word, does blocking. Therefore,
grabbing lock must be avoided IMHO

> ? spin_unlock_bh(&xgr_learn_lock);
>
> ?if (piga_on == 1) {
> /*
> * Here my hypercall make a kernel panic with this error:
> * ??????????? " divide error: 0000 [#1] SMP"
> */
> ??????????????? spin_lock_bh(&xgr_learn_lock);
> ??????????????? set_current_state(TASK_UNINTERRUPTIBLE);

wait wait, why setting as uninterruptible?

> ??????????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> long)piga_seq_cpt);
> ??????????????? set_current_state(TASK_RUNNING);
> ??????????????? spin_lock_bh(&xgr_learn_lock);
> }
> }
>
>
>
>
>
>> Date: Wed, 8 Jun 2011 15:52:33 +0530
>> Subject: Re: Problems with hypercalls
>> From: fs.rajat at gmail.com
>> To: mulyadi.santosa at gmail.com
>> CC: tricheurs at hotmail.fr; kernelnewbies at kernelnewbies.org
>>
>> are you doing 64bit devision on 32 bit arch? If that is the case,
>> do_div is worth considering.
>>
>> On Wed, Jun 8, 2011 at 3:25 PM, Mulyadi Santosa
>> <mulyadi.santosa@gmail.com> wrote:
>> > On Tue, Jun 7, 2011 at 15:39, emilie lefebvre <tricheurs@hotmail.fr>
>> > wrote:
>> >> "divide error: 0000 [#1] SMP
>> >> ...
>> >> ?[<ffffffff813f8cdd>] panic+0x78/0x137
>> >> ?[<ffffffff813fcb94>] oops_end+0xe4/0x100
>> >> ?[<ffffffff8101021b>] die+0x5b/0x90
>> >> ?[<ffffffff813fc444>] do_trap+0xc4/0x160
>> >> ?[<ffffffff8100df2f>] do_divide_error+0x8f/0xb0
>> >> ?[<ffffffff811f974c>] ? my_function+0xdc/0xe70 "
>> >>
>> >> Could you have any suggestions ?
>> >
>> > Could you show us your code? perhaps by pasting them somewhere?
>> >
>> > >From what I guess, sounds like your code did some math (directly or
>> > indirectly) that fiddle with floating point numbers?
>> >
>> >
>> > --
>> > regards,
>> >
>> > Mulyadi Santosa
>> > Freelance Linux trainer and consultant
>> >
>> > blog: the-hydra.blogspot.com
>> > training: mulyaditraining.blogspot.com
>> >
>> > _______________________________________________
>> > Kernelnewbies mailing list
>> > Kernelnewbies at kernelnewbies.org
>> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>



-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

Problems with hypercalls

[Peter Teoh]

perhaps this example will provide u with more info:

http://a380.informatik.uni-bremen.de/lxr/source/arch/x86/lguest/boot.c

I think the correct step is to disable IRQ instead - before every call
to kvm_hypercallX().   The reason is given in the remark:

110         /*
111          * Disable interrupts if not already disabled: we don't want an
112          * interrupt handler making a hypercall while we're already doing
113          * one!
114          */

On Wed, Jun 8, 2011 at 10:54 PM, emilie lefebvre <tricheurs@hotmail.fr> wrote:
>
> This is my function :
>
> static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;
> static int piga_seq_cpt = 1;
>
> /*
> * Function called for each systemcall (Hook SELinux avc function)
> */
> int piga_control(u32 ssid, ...., struct av_decision * avd) {
>
> /*
> * Here my hypercall work but block my vm with this error :
> * ?????????????? " BUG: scheduling while atomic ... "
> */
>
> spin_lock_bh(&xgr_learn_lock);
> ? if ( in_atomic())
> ?????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> long)piga_seq_cpt);
> ? spin_unlock_bh(&xgr_learn_lock);
>
> ?if (piga_on == 1) {
> /*
> * Here my hypercall make a kernel panic with this error:
> * ??????????? " divide error: 0000 [#1] SMP"
> */
> ??????????????? spin_lock_bh(&xgr_learn_lock);
> ??????????????? set_current_state(TASK_UNINTERRUPTIBLE);
> ??????????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> long)piga_seq_cpt);
> ??????????????? set_current_state(TASK_RUNNING);
> ??????????????? spin_lock_bh(&xgr_learn_lock);
> }
> }
>
>

I think u generally set TASK_UNINTERRUPTIBLE whenever about to modify
the scheduling task list (eg, wait queue manipulation) or about to
call "schedule()" (ie, doing your own scheduling).   The function
set_current_state() literally just set the variable value only, it
does not disable interrupt.

-- 
Regards,
Peter Teoh

Problems with hypercalls

[emilie lefebvre]

Hi, 

I try this :


 local_irq_save(flags);

 kvm_hypercall2 ( 6, 2, 2);

 local_irq_restore(flags);



But I still have my kernel panic with  "divide error: 0000 [#1] SMP" that I don't understand!

with or without lock, nothing change, the same when I change the current state.



I tried to move my hypercall and I still don't understand why it works just before my test

"if (piga_on == 1)" without any protections (like disable interrupts) and not after..



 Thank you for trying to help me


> Date: Thu, 9 Jun 2011 09:46:12 +0800
> Subject: Re: Problems with hypercalls
> From: htmldeveloper at gmail.com
> To: tricheurs at hotmail.fr
> CC: kernelnewbies at kernelnewbies.org
> 
> perhaps this example will provide u with more info:
> 
> http://a380.informatik.uni-bremen.de/lxr/source/arch/x86/lguest/boot.c
> 
> I think the correct step is to disable IRQ instead - before every call
> to kvm_hypercallX().   The reason is given in the remark:
> 
> 110         /*
> 111          * Disable interrupts if not already disabled: we don't want an
> 112          * interrupt handler making a hypercall while we're already doing
> 113          * one!
> 114          */
> 
> On Wed, Jun 8, 2011 at 10:54 PM, emilie lefebvre <tricheurs@hotmail.fr> wrote:
> >
> > This is my function :
> >
> > static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;
> > static int piga_seq_cpt = 1;
> >
> > /*
> > * Function called for each systemcall (Hook SELinux avc function)
> > */
> > int piga_control(u32 ssid, ...., struct av_decision * avd) {
> >
> > /*
> > * Here my hypercall work but block my vm with this error :
> > *                " BUG: scheduling while atomic ... "
> > */
> >
> > spin_lock_bh(&xgr_learn_lock);
> >   if ( in_atomic())
> >            kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> > long)piga_seq_cpt);
> >   spin_unlock_bh(&xgr_learn_lock);
> >
> >  if (piga_on == 1) {
> > /*
> > * Here my hypercall make a kernel panic with this error:
> > *             " divide error: 0000 [#1] SMP"
> > */
> >                 spin_lock_bh(&xgr_learn_lock);
> >                 set_current_state(TASK_UNINTERRUPTIBLE);
> >                 kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> > long)piga_seq_cpt);
> >                 set_current_state(TASK_RUNNING);
> >                 spin_lock_bh(&xgr_learn_lock);
> > }
> > }
> >
> >
> 
> I think u generally set TASK_UNINTERRUPTIBLE whenever about to modify
> the scheduling task list (eg, wait queue manipulation) or about to
> call "schedule()" (ie, doing your own scheduling).   The function
> set_current_state() literally just set the variable value only, it
> does not disable interrupt.
> 
> -- 
> Regards,
> Peter Teoh
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110609/875b6475/attachment-0001.html 

Problems with hypercalls

[Peter Teoh]

I guessed the cause of the error is really somewhere else - nothing to
do with this part.   But without a full view of the entire source - it
is hard to diagnose the bugs. (Perhaps even more difficult if full
view is available).   But I have no problem insmod lg.ko in
drivers/lguest directory (after CONFIG_LGUEST is set to "m"), and
lguest is not a simple example I must say.   And to get a better
understanding on how to use the kvm_hypercall APIs, just go to the
kernel source's drivers/lguest directory and enter "make" and it will
churns lots of information (totalling about 7000+ lines) teaching you
the basic of KVM - both how the KVM hypervisor works, and how the
lguest work.

And if u are lazy to do a "make" this is my version:

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B1hg6_FvnEa8ZjFjMDQxNzAtZDAyZC00MDA2LTk3YmMtNGE5YjdjZDM0Nzc3&hl=en_US

On Thu, Jun 9, 2011 at 4:35 PM, emilie lefebvre <tricheurs@hotmail.fr> wrote:
> Hi,
> I try this :
>
> ?local_irq_save(flags);
> ?kvm_hypercall2 ( 6, 2, 2);
> ?local_irq_restore(flags);
>
> But I still have my kernel panic with "divide error: 0000 [#1] SMP" that I
> don't understand!
> with or without lock, nothing change, the same when I change the current
> state.
>
> I tried to move my hypercall and I still don't understand why it works just
> before my test
> "if (piga_on == 1)" without any protections (like disable interrupts) and
> not after..
>
> Thank you for trying to help me
>
>
>> Date: Thu, 9 Jun 2011 09:46:12 +0800
>> Subject: Re: Problems with hypercalls
>> From: htmldeveloper at gmail.com
>> To: tricheurs at hotmail.fr
>> CC: kernelnewbies at kernelnewbies.org
>>
>> perhaps this example will provide u with more info:
>>
>> http://a380.informatik.uni-bremen.de/lxr/source/arch/x86/lguest/boot.c
>>
>> I think the correct step is to disable IRQ instead - before every call
>> to kvm_hypercallX(). The reason is given in the remark:
>>
>> 110 /*
>> 111 * Disable interrupts if not already disabled: we don't want an
>> 112 * interrupt handler making a hypercall while we're already doing
>> 113 * one!
>> 114 */
>>
>> On Wed, Jun 8, 2011 at 10:54 PM, emilie lefebvre <tricheurs@hotmail.fr>
>> wrote:
>> >
>> > This is my function :
>> >
>> > static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;
>> > static int piga_seq_cpt = 1;
>> >
>> > /*
>> > * Function called for each systemcall (Hook SELinux avc function)
>> > */
>> > int piga_control(u32 ssid, ...., struct av_decision * avd) {
>> >
>> > /*
>> > * Here my hypercall work but block my vm with this error :
>> > * ?????????????? " BUG: scheduling while atomic ... "
>> > */
>> >
>> > spin_lock_bh(&xgr_learn_lock);
>> > ? if ( in_atomic())
>> > ?????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
>> > long)piga_seq_cpt);
>> > ? spin_unlock_bh(&xgr_learn_lock);
>> >
>> > ?if (piga_on == 1) {
>> > /*
>> > * Here my hypercall make a kernel panic with this error:
>> > * ??????????? " divide error: 0000 [#1] SMP"
>> > */
>> > ??????????????? spin_lock_bh(&xgr_learn_lock);
>> > ??????????????? set_current_state(TASK_UNINTERRUPTIBLE);
>> > ??????????????? kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
>> > long)piga_seq_cpt);
>> > ??????????????? set_current_state(TASK_RUNNING);
>> > ??????????????? spin_lock_bh(&xgr_learn_lock);
>> > }
>> > }
>> >
>> >
>>
>> I think u generally set TASK_UNINTERRUPTIBLE whenever about to modify
>> the scheduling task list (eg, wait queue manipulation) or about to
>> call "schedule()" (ie, doing your own scheduling). The function
>> set_current_state() literally just set the variable value only, it
>> does not disable interrupt.
>>
>> --
>> Regards,
>> Peter Teoh
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>



-- 
Regards,
Peter Teoh