KVM: Fix fs/gs reload oops with invalid ldt

KVM: Fix fs/gs reload oops with invalid ldt

commit 9581d442b9058d3699b4be568b6e5eae38a41493 upstream.

kvm reloads the host's fs and gs blindly, however the underlying segment
descriptors may be invalid due to the user modifying the ldt after loading
them.

Fix by using the safe accessors (loadsegment() and load_gs_index()) instead
of home grown unsafe versions.

This is CVE-2010-3698.

KVM-Stable-Tag.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>