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

[Igor Mammedov]

On Thu, 20 Jun 2019 22:46:15 -0300
Eduardo Habkost <address@hidden> wrote:

> 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.
Indeed, sorry for not testing before posting patch.
I'll send properly tested v2.

> 
> 
> > > 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);
> > >  }
> > >   
> >   
>