Date: Thu, 3 Feb 2000 10:57:11 +0100 From: "Thomas Klein" <Thomas.Klein@KryptoKom.DE> To: freebsd-hackers@FreeBSD.org Subject: Re: how to catch a wildrunning pointer Message-ID: <C125687A.0036ACF0.00@nt-notes.kryptokom.de>
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Alfred Perlstein <bright@wintelcom.net> on 28.01.2000 11:49:34
To: Thomas Klein/Aachen/Utimaco/DE@utimaco
cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: how to catch a wildrunning pointer
> >
> > Hi
> >
> > My Problem:
> > Within a kernel timeout routine I allocate memory and fill it with data.
> > After a while I lock at this data again and realize that it it was modifyted
> > (but not by me).
> > How can I set a kernel mode watch point to that data to see which function
> > change the data.
> >
> > Any Ideas ????
>
> Look at the vm code, you can probably write protect the pages while
> you aren't accessing them, this will cause offending code to panic
> the machine so you can figure out who is twiddling your bits.
>
> Of course you'll have to unprotect the memory when you want to access
> it for legitimate reasons.
>
> You owe the oracle a how-to on acually doing this, a paragraph or two
> would suffice.
>
> thanks,
> -Or^H^HAlfred
If I understand this correctly I have to use the pmap_protect function.
For testing I integrate the following sequence within a device driver
attach routine.
{
int i;
char * t_ptr;
t_ptr = (char*) malloc(1027,M_DEVBUF,M_NOWAIT);
for(i=0;i<1027,i++)
*t_ptr = 'x';
pmap_protect(kmem_map,t_ptr,t_prt + 1027,VM_PROT_READ);
*t_ptr = 'A';
printf("I can see this\n");
}
No exception ocured.
What is wrong?
Wy dosn't it work?
Regards Thomas
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