Modify cr0 at dom0

[machi1271 <machi1271@gmail.com>]

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hi,
Background:
I want to hook the syscalls for dom0. So, I get the syscall_enter address by calling HYPERVISOR_domctl, with xen_domctl.cmd = XEN_DOMCTL_getvcpucontext.
The returned ctx.syscall_callback_eip is correct, and I find the syscall_table address from the syscall_callback_eip.
Now, my target is to modify the original syscall_table, and I know I should clear the CR0.WP bit before modify.

However, when I try to set cr0 back to hypervisor after the cr0.WP being cleared through HYPERVISOR_domctl(with xen_domctl.cmd = XEN_DOMCTL_setvcpucontext), 
dom0 DEAD. 

I traced into the hypercall, and I find the program dead in the following while loop:
void vcpu_sleep_sync(struct vcpu *v)
{
    vcpu_sleep_nosync(v);

    while ( !vcpu_runnable(v) && v->is_running )
        cpu_relax();

    sync_vcpu_execstate(v);
}
in domain_pause.

Why? Is Calling XEN_DOMCTL_setvcpucontext from dom0 not allowed? Or, is there another way to make the memory area protected by WP to be writable?

I am running my code on 2.6.18-194.el5xen., no domain is running except dom0.

Regards~




machi1271

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