x86/vvmx: check vmcs address in vmread/vmwrite

If nested vmcs's address is invalid, virtual_vmcs_enter() will fail
during vmread/vmwrite:

(XEN) Xen BUG at .../git/upstream/xen/xen/include/asm/hvm/vmx/vmx.h:333
(XEN) ----[ Xen-4.9-unstable  x86_64  debug=y   Tainted:    H ]----
(XEN) Xen call trace:
(XEN)    [<ffff82d0801f925e>] vmcs.c#arch/x86/hvm/vmx/vmcs.o.unlikely+0x28/0x19a
(XEN)    [<ffff82d0801f60e3>] virtual_vmcs_vmwrite_safe+0x16/0x52
(XEN)    [<ffff82d080202cb2>] nvmx_handle_vmwrite+0x70/0xfe
(XEN)    [<ffff82d0801fe98a>] vmx_vmexit_handler+0x1379/0x1c49
(XEN)    [<ffff82d08020427c>] vmx_asm_vmexit_handler+0x3c/0x120

Fix this by emulating VMfailInvalid if the address is invalid.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>

xen/arch/x86/hvm/vmx/vvmx.c

@@ -1759,6 +1759,12 @@ int nvmx_handle_vmread(struct cpu_user_regs *regs)
     if ( rc != X86EMUL_OKAY )
         return rc;
 
+    if ( vcpu_nestedhvm(v).nv_vvmcxaddr == INVALID_PADDR )
+    {
+        vmfail_invalid(regs);
+        return X86EMUL_OKAY;
+    }
+
     rc = get_vvmcs_safe(v, reg_read(regs, decode.reg2), &value);
     if ( rc != VMX_INSN_SUCCEED )
     {
@@ -1796,6 +1802,12 @@ int nvmx_handle_vmwrite(struct cpu_user_regs *regs)
              != X86EMUL_OKAY )
         return X86EMUL_EXCEPTION;
 
+    if ( vcpu_nestedhvm(v).nv_vvmcxaddr == INVALID_PADDR )
+    {
+        vmfail_invalid(regs);
+        return X86EMUL_OKAY;
+    }
+
     vmcs_encoding = reg_read(regs, decode.reg2);
     err = set_vvmcs_safe(v, vmcs_encoding, operand);
     if ( err != VMX_INSN_SUCCEED )