linux-kernel - Re: [niks:has_ioport_v3] [tty] aa0652d7f1: BUG:kernel_NULL_pointer

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Date:   Mon, 09 Jan 2023 09:45:04 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        kernel test robot <yujie.liu@...el.com>
Cc:     oe-lkp@...ts.linux.dev, kernel test robot <lkp@...el.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [niks:has_ioport_v3] [tty] aa0652d7f1:
 BUG:kernel_NULL_pointer_dereference,address

On Thu, 2023-01-05 at 09:03 +0100, Arnd Bergmann wrote:
> 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

Thanks for looking into it Arnd, your reasoning makes sense to me, I'll
try to look into this and test this case before I sent out the v3 of
the HAS_IOPORT patches. I still also have a few nitpicks from Bjorn,
mostly about the commit messages, to work in. Hope to do that soon but
got a few things going on at the moment.