Re: [Xen-devel] Intercepting page access

[HANNAS YAYA Issa <issa.hannasyaya@xxxxxxxxxxx>]

Hi
I really really need help. I continue trying to make it work but 
nothing change.
Please I need help :(





On Sat, 18 Apr 2015 19:25:52 +0200, HANNAS YAYA Issa wrote:
Hi I am working in a research project

I want to incercept pages access by guest virtual machine.
My approach is setting higher priviledge in pages by setting changing
the user/sypervisor priviledge bit in page table entry associated to
this page. Here is the piece of code used

void remove_access(l1_pgentry_t *pl1e){
l1_pgentry_t ol1e;
l1_pgentry_t nl1e;
unsigned int  nmfn;
if(__copy_from_user(&ol1e, pl1e, sizeof(ol1e)) == 0){
nl1e = ol1e;
nmfn = l1e_get_pfn(ol1e);

if(!(l1e_get_flags(ol1e)&_PAGE_GUEST_KERNEL))
{
l1e_remove_flags(nl1e, _PAGE_USER);
if(__copy_to_guest(pl1e, &nl1e,
sizeof(nl1e)) != 0)
printk("entry cannot be copied\n");
flush_tlb_all();
}
}else
printk("copy from user failed\n");
}

the pointer pl1e is obtained when PTE is updated (in do_mm_update).
in page fault handler (do_page_fault). I reset the access by this code

void reset_access(l1_pgentry_t *pl1e, l1_pgentry_t ol1e)
{
l1_pgentry_t nl1e = ol1e;
l1e_add_flags(nl1e, _PAGE_USER);
__copy_to_guest(pl1e, &nl1e, sizeof(nl1e));
flush_tlb_all();
return;
}




but the problem is that my computer crash and it reboots. I don't
know what is wrong with my code. I spend 2 weeks trying to solve this
problem but I couldn't. Please I really need your help

Thank you

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