CVE-2025-39725

In the Linux kernel, the following vulnerability has been resolved:

mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list

In shrink_folio_list(), the hwpoisoned folio may be large folio, which

can't be handled by unmap_poisoned_folio(). For THP, try_to_unmap_one()

must be passed with TTU_SPLIT_HUGE_PMD to split huge PMD first and then

retry. Without TTU_SPLIT_HUGE_PMD, we will trigger null-ptr deref of

pvmw.pte. Even we passed TTU_SPLIT_HUGE_PMD, we will trigger a

WARN_ON_ONCE due to the page isn't in swapcache.

Since UCE is rare in real world, and race with reclaimation is more rare,

just skipping the hwpoisoned large folio is enough. memory_failure() will

handle it if the UCE is triggered again.

This happens when memory reclaim for large folio races with

memory_failure(), and will lead to kernel panic. The race is as

follows:

cpu0 cpu1

shrink_folio_list memory_failure

TestSetPageHWPoison

unmap_poisoned_folio

--> trigger BUG_ON due to

unmap_poisoned_folio couldn't

handle large folio

[[email protected]: add comment to unmap_poisoned_folio()]