Re: [Qemu-devel] [PATCH] pc: fix possible NULL pointer dereference in pc_machine_get_device_memory_region_size()

[Paolo Bonzini]

On 10/06/19 15:50, Igor Mammedov wrote:
> QEMU will crash when device-memory-region-size property is read if 
> ms->device_memory
> wasn't initialized yet.
> 
> Crash can be reproduced with:
>  $QEMU -preconfig -qmp unix:qmp_socket,server,nowait &
>  ./scripts/qmp/qom-get -s qmp_socket /machine.device-memory-region-size
> 
> Instead of crashing return 0 if ms->device_memory hasn't been initialized.

This patch breaks bios-tables-test /x86_64/acpi/piix64/cpuhp:

acpi-test: Warning! SRAT binary file mismatch. Actual [aml:/tmp/aml-RIFK3Z], 
Expected [aml:tests/data/acpi/pc/SRAT.memhp].
acpi-test: Warning! SRAT mismatch. Actual [asl:/tmp/asl-TLFK3Z.dsl, 
aml:/tmp/aml-RIFK3Z], Expected [asl:/tmp/asl-JL5J3Z.dsl, 
aml:tests/data/acpi/pc/SRAT.memhp].
**
ERROR:/home/pbonzini/work/upstream/qemu/tests/bios-tables-test.c:434:test_acpi_asl:
 assertion failed: (all_tables_match)
ERROR - Bail out! 
ERROR:/home/pbonzini/work/upstream/qemu/tests/bios-tables-test.c:434:test_acpi_asl:
 assertion failed: (all_tables_match)

So I'm removing it from the pull request.

Paolo

> Signed-off-by: Igor Mammedov <address@hidden>
> ---
> v2:
>   add reproducer to commit message
>    (Markus Armbruster <address@hidden>)
> 
>  hw/i386/pc.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index edc240b..1b7ead9 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -2459,7 +2459,11 @@ pc_machine_get_device_memory_region_size(Object *obj, 
> Visitor *v,
>                                           Error **errp)
>  {
>      MachineState *ms = MACHINE(obj);
> -    int64_t value = memory_region_size(&ms->device_memory->mr);
> +    int64_t value = 0;
> +
> +    if (ms->device_memory) {
> +        memory_region_size(&ms->device_memory->mr);
> +    }
>  
>      visit_type_int(v, name, &value, errp);
>  }
>