Re: Kprobes might be stealing int3

[Prasanna S Panchamukhi <prasanna@in.ibm.com>]

Bibo,

In fact, Stas earlier had pointed this problem on the lkml and
I had posted a patch to fix it.
URL for this patch is below.
http://lkml.org/lkml/2004/12/9/43

Thanks
Prasanna



On Fri, Feb 24, 2006 at 08:56:47AM +0800, Mao, Bibo wrote:
> Anil,
> I search the x86 assembly manual, about INT instruction there are three kinds:
> 	CC 		INT 3 		Interrupt 3―trap to debugger
> 	CD ib 	INT imm8 		Interrupt vector number specified by immediate byte
> 	CE 		INTO 		Interrupt 4―if overflow flag is 1
> So like this test program, the instruction encoding will be 0x03cd, it has the same effect with 0xcc encoding. 
> And currently in kprobe BREAK_INSTRUCTION is only defined as 0xcc. Maybe another encoding also need be judged.
> 
> Thanks
> bibo,mao
> 
> >-----Original Message-----
> >From: systemtap-owner@sourceware.org [mailto:systemtap-owner@sourceware.org]
> >On Behalf Of Keshavamurthy, Anil S
> >Sent: 2006年2月24日 7:34
> >To: systemtap@sources.redhat.com
> >Subject: FW: Kprobes might be stealing int3
> >
> >I went little further and found why the application is segmentation
> >fault'ing.
> >
> >In the kprobes_handler() code, we are checking
> >If (*addr != BREAK_INSTRUCTION)  and this is where the
> >app is crashing since we are trying to dereference this address
> >which is not a linear address.
> >
> >I would be happy to tryout any fix that any one provides.
> >
> >Thanks,
> >Anil
> >-----Original Message-----
> >From: Keshavamurthy Anil S [mailto:anil.s.keshavamurthy@intel.com]
> >Sent: Thursday, February 23, 2006 12:11 PM
> >To: Systemtap
> >Cc: Keshavamurthy, Anil S
> >Subject: Kprobes might be stealing int3
> >
> >Hi,
> >	I tried running the below program on both
> >x86_64 and i386 and on both architecture,
> >if the kernel is compiled with CONFIG_KPROBES,
> >my below application segmentation faults.
> >
> >On kernel where CONFIG_KPROBES set to N, the
> >same test program passes.
> >
> >Here goes the test program...
> >-------------------------
> >#include <stdlib.h>
> >#include <signal.h>
> >
> >void my_trap(int sig)
> >{
> > printf("Test passed, all OK\n");
> > exit(0);
> >}
> >
> >int main()
> >{
> > signal(SIGTRAP, my_trap);
> > asm volatile (".byte 0xcd,3");
> > printf("Stolen interrupt, very bad!\n");
> >}
> >----------------------------------
> >
> >
> >
> >
> >
> >

-- 
Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@in.ibm.com
Ph: 91-80-51776329