CVE-2026-93238
Received Received - Intake

Use of Uninitialized apm_filtered Bitmap in Linux Kernel

Publication date: 2026-09-24

Last updated on: 2026-09-24

Assigner: kernel.org

Description
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().

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Meta Information

Published
2026-09-24
Last Modified
2026-09-24
Generated
2026-09-25
AI Q&A
2026-09-24
EPSS Evaluated
N/A
NVD
CVE-2026-93238
EUVD
EUVD-2026-86244

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a Linux kernel vulnerability where a bitmap used for filtering AP devices is not properly initialized. The apm_filtered bitmap is allocated on the stack without zeroing its contents, meaning it may contain arbitrary memory values. If certain conditions are met during hot plug configuration changes, this uninitialized bitmap is passed to a function that resets hardware queues based on the bitmap's bits. This could cause unintended resets of guest hardware queues due to the garbage values in the bitmap.

Detection Guidance

This vulnerability is specific to the Linux kernel's s390/vfio-ap driver and requires kernel-level inspection. Detection involves checking kernel logs for related errors or verifying the presence of the vulnerable code path. No direct network detection commands are applicable.

Impact Analysis

If you use the Linux kernel with VFIO AP (Virtual Function I/O for Adjunct Processor) devices, this vulnerability could cause unexpected hardware resets. This might lead to guest virtual machines experiencing sudden disruptions or crashes if their hardware queues are incorrectly reset. The impact is limited to systems using VFIO AP devices with specific hot plug configurations.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA. It is a low-level kernel issue in the Linux s390/vfio-ap driver that could lead to unintended hardware resets but does not involve data exposure or privacy violations typical of compliance concerns.

Mitigation Strategies

Apply the kernel patch that zero-initializes the apm_filtered bitmap in vfio_ap_mdev_hot_plug_cfg(). Update to a Linux kernel version containing the fix. If patching is not immediately possible, avoid modifying hot plug configurations for control domains until patched.

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