s390/vfio-ap: fix potential use of uninitialized apm_filtered bitmap

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: fix potential use of uninitialized apm_filtered bitmap 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().

Source published

24 Sep 2026 15:34:11 UTC

Source modified

19 Oct 2026 09:07:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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