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

[Eduardo Habkost]

On Fri, Jun 21, 2019 at 02:29:29AM +0200, Paolo Bonzini wrote:
> 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.

The patch makes all memory regions return 0 as its size.


> > 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);

This was supposed to be:

        value = memory_region_size(&ms->device_memory->mr);

> > +    }
> >  
> >      visit_type_int(v, name, &value, errp);
> >  }
> > 
> 

-- 
Eduardo