CVE-2025-39725: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel has been identified and assigned CVE-2025-39725, which affects the memory management subsystem, specifically related to hardware poisoned large folio handling in shrinkfoliolist. The issue was discovered and disclosed on September 5, 2025 (NVD).

The vulnerability occurs in shrinkfoliolist() function where hardware poisoned folio may be a large folio that cannot be handled by unmappoisonedfolio(). For Transparent Huge Pages (THP), trytounmapone() requires TTUSPLITHUGEPMD flag to split huge PMD first before retrying. Without this flag, it triggers a null-pointer dereference of pvmw.pte. Even with TTUSPLITHUGEPMD, it triggers a WARNONONCE due to the page not being in swapcache. The issue manifests when memory reclaim for large folio races with memoryfailure() (NVD). Red Hat has assigned this vulnerability a CVSS v3.1 base score of 7.0 (High) with attack vector being Local and attack complexity being High (Red Hat).

When exploited, this vulnerability can lead to kernel panic, potentially causing system crashes and denial of service. The issue specifically impacts systems using large folios in memory management, particularly when uncorrectable errors (UCE) occur during memory reclamation (NVD).

The recommended mitigation is to skip the hardware poisoned large folio handling, allowing memory_failure() to handle it if the uncorrectable error is triggered again. This approach is considered sufficient given the rarity of UCE in real-world scenarios and the even rarer occurrence of races with reclamation (NVD).