target/i386: Generate #UD for LOCK on a register increment

Fix a TCG crash due to attempting an atomic increment
operation without having set up the address first.
This is a similar case to that dealt with in commit
e84fcd7f662a0d8198703, and we fix it in the same way.

Fixes: https://bugs.launchpad.net/qemu/+bug/1807675
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20190328104750.25046-1-peter.maydell@linaro.org

diff --git a/target/i386/translate.c b/target/i386/translate.c
index 49cd298374bbbacef705624cbab33efee58413cf..b725bec37cd75bf1b379ff226e9a09455910dc52 100644 (file)
--- a/target/i386/translate.c
+++ b/target/i386/translate.c
@@ -1398,6 +1398,11 @@ static void gen_op(DisasContext *s1, int op, TCGMemOp ot, int d)
 static void gen_inc(DisasContext *s1, TCGMemOp ot, int d, int c)
 {
     if (s1->prefix & PREFIX_LOCK) {
+        if (d != OR_TMP0) {
+            /* Lock prefix when destination is not memory */
+            gen_illegal_opcode(s1);
+            return;
+        }
         tcg_gen_movi_tl(s1->T0, c > 0 ? 1 : -1);
         tcg_gen_atomic_add_fetch_tl(s1->T0, s1->A0, s1->T0,
                                     s1->mem_index, ot | MO_LE);