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Date:   Thu, 05 Jan 2023 09:03:40 +0100
From:   "Arnd Bergmann" <arnd@kernel.org>
To:     "kernel test robot" <yujie.liu@intel.com>,
        "Niklas Schnelle" <schnelle@linux.ibm.com>
Cc:     oe-lkp@lists.linux.dev, "kernel test robot" <lkp@intel.com>,
        linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [niks:has_ioport_v3] [tty] aa0652d7f1:
 BUG:kernel_NULL_pointer_dereference,address
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On Thu, Jan 5, 2023, at 06:54, kernel test robot wrote:
> Greeting,
>
> FYI, we noticed BUG:kernel_NULL_pointer_dereference,address due to 
> commit (built with clang-14):
>
> commit: aa0652d7f1b311e55232a8153522fdaaba0f197a ("tty: serial: handle 
> HAS_IOPORT dependencies")
> https://git.kernel.org/cgit/linux/kernel/git/niks/linux.git 
> has_ioport_v3
>
> in testcase: boot
>
> on test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -m 4G
>
> caused below changes (please refer to attached dmesg/kmsg for entire 
> log/backtrace):
>
>
> [    2.166733][    T0] calling  univ8250_console_init+0x0/0x30 @ 0
> [    2.167555][    T0] BUG: kernel NULL pointer dereference, address: 
> 00000000

I think it's this bit:

@@ -508,12 +523,13 @@ static void set_io_from_upio(struct uart_port *p)
                up->dl_read = au_serial_dl_read;
                up->dl_write = au_serial_dl_write;
                break;
-#endif
-
+#ifdef CONFIG_HAS_IOPORT
        default:
                p->serial_in = io_serial_in;
                p->serial_out = io_serial_out;
                break;
+#endif
+#endif
        }
        /* Remember loaded iotype */
        up->cur_iotype = p->iotype;


which puts the 'default' case inside of '#ifdef
CONFIG_SERIAL_8250_RT288X'. x86 does not use the
RT288x variant but relies on the default, so any
call to io_serial_{in,out} will cause a NULL
pointer dereference.

       Arnd