target/microblaze: Fix possible array out of bounds in mmu_write()

The size of env->mmu.regs is 3, but the range of 'rn' is [0, 5].
To avoid data access out of bounds, only if 'rn' is less than 3, we
can print env->mmu.regs[rn]. In other cases, we can print
env->mmu.regs[MMU_R_TLBX].

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Alex Chen <alex.chen@huawei.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-Id: <5FA10ABA.1080109@huawei.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

target/microblaze/mmu.c

@@ -234,7 +234,8 @@ void mmu_write(CPUMBState *env, bool ext, uint32_t rn, uint32_t v)
     unsigned int i;
 
     qemu_log_mask(CPU_LOG_MMU,
-                  "%s rn=%d=%x old=%x\n", __func__, rn, v, env->mmu.regs[rn]);
+                  "%s rn=%d=%x old=%x\n", __func__, rn, v,
+                  rn < 3 ? env->mmu.regs[rn] : env->mmu.regs[MMU_R_TLBX]);
 
     if (cpu->cfg.mmu < 2 || !cpu->cfg.mmu_tlb_access) {
         qemu_log_mask(LOG_GUEST_ERROR, "MMU access on MMU-less system\n");