KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor()

Per Intel's SDM on the "Instruction Set Reference", when
loading segment descriptor, not-present segment check should
be after all type and privilege checks. But the emulator checks
it first, then #NP is triggered instead of #GP if privilege fails
and segment is not present. Put not-present segment check after
type and privilege checks in __load_segment_descriptor().

Fixes: 38ba30ba51a00 (KVM: x86 emulator: Emulate task switch in emulator.c)
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Message-Id: <52573c01d369f506cadcf7233812427cf7db81a7.1644292363.git.houwenlong.hwl@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b7990defca9cf10cac6a61a6343becd7b56bc17f..a6c54b8fdbc7b0f8e51841e07333d43bd9469988 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1608,11 +1608,6 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                goto exception;
        }
 
-       if (!seg_desc.p) {
-               err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
-               goto exception;
-       }
-
        dpl = seg_desc.dpl;
 
        switch (seg) {
@@ -1652,6 +1647,10 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
        case VCPU_SREG_TR:
                if (seg_desc.s || (seg_desc.type != 1 && seg_desc.type != 9))
                        goto exception;
+               if (!seg_desc.p) {
+                       err_vec = NP_VECTOR;
+                       goto exception;
+               }
                old_desc = seg_desc;
                seg_desc.type |= 2; /* busy */
                ret = ctxt->ops->cmpxchg_emulated(ctxt, desc_addr, &old_desc, &seg_desc,
@@ -1676,6 +1675,11 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                break;
        }
 
+       if (!seg_desc.p) {
+               err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
+               goto exception;
+       }
+
        if (seg_desc.s) {
                /* mark segment as accessed */
                if (!(seg_desc.type & 1)) {