CVE-2023-54267: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54267 is a Linux kernel vulnerability in the powerpc/pseries subsystem involving an improper preemption check in the lppaca_shared_proc() function. When DEBUG_PREEMPT is enabled, accessing /proc/powerpc/lparcfg triggers a spurious BUG: using smp_processor_id() in preemptible code warning, causing errors on IBM POWER (pSeries) systems. The vulnerability was published on December 30, 2025, and affects Linux kernel versions prior to the fixes backported to stable branches (5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, and 6.6). The EPSS score is approximately 0.024% (very low), and no CVSS base score has been formally assigned by the assigner (EUVD, Feedly).

The root cause is an incorrect assumption in lppaca_shared_proc(), which accepted a pointer to the lppaca structure typically obtained via get_lppaca(). With DEBUG_PREEMPT enabled, calling get_lppaca() internally invokes smp_processor_id(), which triggers a kernel preemption check and raises a BUG warning when called from preemptible context (e.g., during a read of /proc/powerpc/lparcfg). The fix reworks lppaca_shared_proc() to directly access the lppaca without taking a pointer, bypassing the preemption check entirely, since the shared processor state is uniform across all lppaca instances. This is a logic/design flaw rather than a memory corruption or privilege escalation issue, and is broadly classified as an improper synchronization or incorrect use of kernel primitives (EUVD, Feedly).

The primary impact is a kernel BUG warning and functional error on IBM POWER (pSeries) systems running Linux kernels with DEBUG_PREEMPT enabled, triggered whenever /proc/powerpc/lparcfg is accessed. This results in a denial of availability for the lparcfg procfs interface, which provides LPAR configuration data. There is no evidence of confidentiality or integrity impact, and the vulnerability does not enable privilege escalation or remote code execution (EUVD, Feedly).

The fix has been backported to multiple stable Linux kernel branches. Administrators should update to the following patched versions or later: 5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, or 6.6. As a temporary workaround on unpatched systems, disabling DEBUG_PREEMPT in the kernel configuration (not recommended for production systems anyway) will prevent the bug from triggering. Distributions such as Red Hat have also issued advisories tracking this issue (EUVD, Feedly).