x86/altp2m: fix HVMOP_altp2m_set_domain_state race

HVMOP_altp2m_set_domain_state does not domain_pause(), presumably
on purpose (as it was originally supposed to cater to a in-guest
agent, and a domain pausing itself is not a good idea).

This can lead to domain crashes in the vmx_vmexit_handler() code
that checks if the guest has the ability to switch EPTP without an
exit. That code can __vmread() the host p2m's EPT_POINTER
(before HVMOP_altp2m_set_domain_state "for_each_vcpu()" has a
chance to run altp2m_vcpu_initialise(), but after
d->arch.altp2m_active is set).

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 410623d437dd76a02c95c08c0fd9388daa5c83a6..79c7d816e24f74219944669d1d08c4ac0cfbca71 100644 (file)
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4538,6 +4538,10 @@ static int do_altp2m_op(
             break;
         }
 
+        rc = domain_pause_except_self(d);
+        if ( rc )
+            break;
+
         ostate = d->arch.altp2m_active;
         d->arch.altp2m_active = !!a.u.domain_state.state;
 
@@ -4556,6 +4560,8 @@ static int do_altp2m_op(
             if ( ostate )
                 p2m_flush_altp2m(d);
         }
+
+        domain_unpause_except_self(d);
         break;
     }