KVM: vmx: VMXOFF emulation in vm86 should cause #UD

Unlike VMCALL, the instructions VMXOFF, VMLAUNCH and VMRESUME should cause a UD
exception in real-mode or vm86.  However, the emulator considers all these
instructions the same for the matter of mode checks, and emulation upon exit
due to #UD exception.

As a result, the hypervisor behaves incorrectly on vm86 mode. VMXOFF, VMLAUNCH
or VMRESUME cause on vm86 exit due to #UD. The hypervisor then emulates these
instruction and inject #GP to the guest instead of #UD.

This patch creates a new group for these instructions and mark only VMCALL as
an instruction which can be emulated.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e5bf13003cd2..a240fac29e76 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3139,12 +3139,8 @@ static int em_clts(struct x86_emulate_ctxt *ctxt)
 
 static int em_vmcall(struct x86_emulate_ctxt *ctxt)
 {
-        int rc;
-
-        if (ctxt->modrm_mod != 3 || ctxt->modrm_rm != 1)
-                return X86EMUL_UNHANDLEABLE;
+        int rc = ctxt->ops->fix_hypercall(ctxt);
 
-        rc = ctxt->ops->fix_hypercall(ctxt);
         if (rc != X86EMUL_CONTINUE)
                 return rc;
 
@@ -3562,6 +3558,12 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
                 F2bv(((_f) | DstReg | SrcMem | ModRM) & ~Lock, _e),     \
                 F2bv(((_f) & ~Lock) | DstAcc | SrcImm, _e)
 
+static const struct opcode group7_rm0[] = {
+        N,
+        I(SrcNone | Priv | EmulateOnUD, em_vmcall),
+        N, N, N, N, N, N,
+};
+
 static const struct opcode group7_rm1[] = {
         DI(SrcNone | Priv, monitor),
         DI(SrcNone | Priv, mwait),
@@ -3655,7 +3657,7 @@ static const struct group_dual group7 = { {
         II(SrcMem16 | Mov | Priv,               em_lmsw, lmsw),
         II(SrcMem | ByteOp | Priv | NoAccess,   em_invlpg, invlpg),
 }, {
-        I(SrcNone | Priv | EmulateOnUD, em_vmcall),
+        EXT(0, group7_rm0),
         EXT(0, group7_rm1),
         N, EXT(0, group7_rm3),
         II(SrcNone | DstMem | Mov,              em_smsw, smsw), N,