x86: make arch_set_info_guest() preemptible

.. as the root page table validation (and the dropping of an eventual
old one) can require meaningful amounts of time.

This is part of CVE-2013-1918 / XSA-45.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>

3 files changed, 13 insertions, 0 deletions

diff --git a/xen/common/compat/domain.c b/xen/common/compat/domain.c
index aac8f46eb5..44ba78ddc7 100644
--- a/xen/common/compat/domain.c
+++ b/xen/common/compat/domain.c
@@ -50,6 +50,10 @@ int compat_vcpu_op(int cmd, int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
         rc = v->is_initialised ? -EEXIST : arch_set_info_guest(v, cmp_ctxt);
         domain_unlock(d);
 
+        if ( rc == -EAGAIN )
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                               cmd, vcpuid, arg);
+
         xfree(cmp_ctxt);
         break;
     }
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 7cca65507d..b5d44d466b 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -938,6 +938,11 @@ long do_vcpu_op(int cmd, int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
         domain_unlock(d);
 
         free_vcpu_guest_context(ctxt);
+
+        if ( rc == -EAGAIN )
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                               cmd, vcpuid, arg);
+
         break;
 
     case VCPUOP_up: {
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 1d00cfc95f..9bd8f8068d 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -368,6 +368,10 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
             domain_pause(d);
             ret = arch_set_info_guest(v, c);
             domain_unpause(d);
+
+            if ( ret == -EAGAIN )
+                ret = hypercall_create_continuation(
+                          __HYPERVISOR_domctl, "h", u_domctl);
         }
 
         free_vcpu_guest_context(c.nat);