KVM: x86 emulator: allow loading null SS in long mode

Null SS is valid in long mode; allow loading it.

Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index db95a55d5936..fe4340f62137 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1324,8 +1324,14 @@ static int load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                 goto load;
         }
 
-        /* NULL selector is not valid for TR, CS and SS */
-        if ((seg == VCPU_SREG_CS || seg == VCPU_SREG_SS || seg == VCPU_SREG_TR)
+        rpl = selector & 3;
+        cpl = ctxt->ops->cpl(ctxt);
+
+        /* NULL selector is not valid for TR, CS and SS (except for long mode) */
+        if ((seg == VCPU_SREG_CS
+             || (seg == VCPU_SREG_SS
+                 && (ctxt->mode != X86EMUL_MODE_PROT64 || rpl != cpl))
+             || seg == VCPU_SREG_TR)
             && null_selector)
                 goto exception;
 
@@ -1352,9 +1358,7 @@ static int load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                 goto exception;
         }
 
-        rpl = selector & 3;
         dpl = seg_desc.dpl;
-        cpl = ctxt->ops->cpl(ctxt);
 
         switch (seg) {
         case VCPU_SREG_SS: