Re: [PATCH] q800: fix segfault with invalid MacROM

[Mark Cave-Ayland]

On 06/01/2022 12:22, Laurent Vivier wrote:

> "qemu-system-m68k -M q800 -bios /dev/null" crahses with a segfault
> in q800_init().
> This happens because the code doesn't check that rom_ptr() returned
> a non-NULL pointer .
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/756
> Reported-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>   hw/m68k/q800.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
> index e4c7c9b88ad0..6261716c8f7e 100644
> --- a/hw/m68k/q800.c
> +++ b/hw/m68k/q800.c
> @@ -672,10 +672,16 @@ static void q800_init(MachineState *machine)
>   
>           /* Remove qtest_enabled() check once firmware files are in the tree */
>           if (!qtest_enabled()) {
> -            if (bios_size < 0 || bios_size > MACROM_SIZE) {
> +            if (bios_size == -1) {
>                   error_report("could not load MacROM '%s'", bios_name);
>                   exit(1);
>               }
> +            if (bios_size != MACROM_SIZE) {
> +                error_report("Invalid size for MacROM '%s': %d bytes,"
> +                             " expected %d bytes", bios_name, bios_size,
> +                             MACROM_SIZE);
> +                exit(1);
> +            }
>   
>               ptr = rom_ptr(MACROM_ADDR, MACROM_SIZE);
>               stl_phys(cs->as, 0, ldl_p(ptr));    /* reset initial SP */

The patch does fix the issue, but it seems a little odd that you can't use -bios 
path/to/m68k-binary to boot with an arbitrary sized binary which could be useful for 
reproducers such as https://gitlab.com/qemu-project/qemu/-/issues/360.

How easy would it be to add the extra rom_ptr() NULL check instead?


ATB,

Mark.