Re: [PATCH v2 6/8] s390/vfio-ap: fix potential use of uninitialized apm_filtered bitmap

[Anthony Krowiak]

On 8/11/26 2:02 PM, Matthew Rosato wrote:
> On 8/10/26 3:22 PM, Anthony Krowiak wrote:
> > The DECLARE_BITMAP(apm_filtered, AP_DEVICES) macro allocates the bitmap
> > on the stack without zero-initializing it.
> >
> > In vfio_ap_mdev_hot_plug_cfg(), the vfio_ap_mdev_filter_matrix() function
> > is only called to initialize and populate apm_filtered if either
> > filter_adapters or filter_domains is true. If the hot plug configuration
> > change only adds control domains (meaning filter_cdoms is true, but
> > filter_adapters and filter_domains are both false),
> > vfio_ap_mdev_filter_matrix() is bypassed.
> >
> > Consequently, apm_filtered is passed to reset_queues_for_apids() with
> > uninitialized stack garbage. This can cause reset_queues_for_apids() to
> > interpret arbitrary stack garbage bits as valid APIDs to reset, potentially
> > performing unintended guest hardware queue resets.
> >
> > Fix this by zero-initializing the apm_filtered bitmap at the beginning of
> > vfio_ap_mdev_hot_plug_cfg() using bitmap_zero().
> >
> > Fixes: eeb386aeb5b7c ("s390/vfio-ap: handle config changed and scan complete notification")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
> Sashiko mentions an unrelated, pre-existing issue with cfg_chg_trigger
> that does not appear to be resolved by this series; please have a look.

I vaguely recall that, but my head is spinning dealing with the plethora of
hades review comments addressing pre-existing issues and it got lost in
the melee. I'll hunt for it.

> You do not necessarily need to add another fix to this series, it could
> be a follow-on.
>
> As for this patch:
>
> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>