target/i386: Generate #UD when applying LOCK to a register destination

Fixes a TCG crash due to attempting the atomic operation without
having set up the address first.  This does not attempt to fix
all of the other missing checks for LOCK.

Fixes: a7cee522
Fixes: https://bugs.launchpad.net/qemu/+bug/1803160Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
Message-Id: <20181113193510.24862-1-richard.henderson@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target/i386/translate.c

@@ -1268,10 +1268,30 @@ static void gen_helper_fp_arith_STN_ST0(int op, int opreg)
     }
 }
 
+static void gen_exception(DisasContext *s, int trapno, target_ulong cur_eip)
+{
+    gen_update_cc_op(s);
+    gen_jmp_im(s, cur_eip);
+    gen_helper_raise_exception(cpu_env, tcg_const_i32(trapno));
+    s->base.is_jmp = DISAS_NORETURN;
+}
+
+/* Generate #UD for the current instruction.  The assumption here is that
+   the instruction is known, but it isn't allowed in the current cpu mode.  */
+static void gen_illegal_opcode(DisasContext *s)
+{
+    gen_exception(s, EXCP06_ILLOP, s->pc_start - s->cs_base);
+}
+
 /* if d == OR_TMP0, it means memory operand (address in A0) */
 static void gen_op(DisasContext *s1, int op, TCGMemOp ot, int d)
 {
     if (d != OR_TMP0) {
+        if (s1->prefix & PREFIX_LOCK) {
+            /* Lock prefix when destination is not memory.  */
+            gen_illegal_opcode(s1);
+            return;
+        }
         gen_op_mov_v_reg(s1, ot, s1->T0, d);
     } else if (!(s1->prefix & PREFIX_LOCK)) {
         gen_op_ld_v(s1, ot, s1->T0, s1->A0);
@@ -2469,21 +2489,6 @@ static void gen_leave(DisasContext *s)
     gen_op_mov_reg_v(s, a_ot, R_ESP, s->T1);
 }
 
-static void gen_exception(DisasContext *s, int trapno, target_ulong cur_eip)
-{
-    gen_update_cc_op(s);
-    gen_jmp_im(s, cur_eip);
-    gen_helper_raise_exception(cpu_env, tcg_const_i32(trapno));
-    s->base.is_jmp = DISAS_NORETURN;
-}
-
-/* Generate #UD for the current instruction.  The assumption here is that
-   the instruction is known, but it isn't allowed in the current cpu mode.  */
-static void gen_illegal_opcode(DisasContext *s)
-{
-    gen_exception(s, EXCP06_ILLOP, s->pc_start - s->cs_base);
-}
-
 /* Similarly, except that the assumption here is that we don't decode
    the instruction at all -- either a missing opcode, an unimplemented
    feature, or just a bogus instruction stream.  */