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

[Matthew Rosato]

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.

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>