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

[Laurent Vivier <laurent@vivier.eu>]

Le 07/01/2022 à 10:47, BALATON Zoltan a écrit :
> On Fri, 7 Jan 2022, Laurent Vivier wrote:
>> Le 07/01/2022 à 09:15, Mark Cave-Ayland a écrit :
>>> 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?
>>>
>>
>> I was thinking that a smaller binary can be padded to 1 MB for use because on a real hardware the 
>> size of the ROM cannot be arbitrary.
>>
>> But it seems reasonable to check only for the NULL pointer rather than the size, I'm going to send 
>> a v2.
> 
> Instead of adding !rom_ptr as well, isn't it enough to change to
> bios_size <= 0 in the existing check?
>

I agree. And to change rom_ptr(MACROM_ADDR, MACROM_SIZE) to rom_ptr(MACROM_ADDR, bios_size)

Thanks,
Laurent