UBUNTU-CVE-2025-22034

In the Linux kernel, the following vulnerability has been resolved: mm/gup: reject FOLL_SPLIT_PMD with hugetlb VMAs Patch series "mm: fixes for device-exclusive entries (hmm)", v2. Discussing the PageTail() call in make_device_exclusive_range() with Willy, I recently discovered [1] that device-exclusive handling does not properly work with THP, making the hmm-tests selftests fail if THPs are enabled on the system. Looking into more details, I found that hugetlb is not properly fenced, and I realized that something that was bugging me for longer -- how device-exclusive entries interact with mapcounts -- completely breaks migration/swapout/split/hwpoison handling of these folios while they have device-exclusive PTEs. The program below can be used to allocate 1 GiB worth of pages and making them device-exclusive on a kernel with CONFIG_TEST_HMM. Once they are device-exclusive, these folios cannot get swapped out (proc$pid/smaps_rollup will always indicate 1 GiB RSS no matter how much one forces memory reclaim), and when having a memory block onlined to ZONE_MOVABLE, trying to offline it will loop forever and complain about failed migration of a page that should be movable. # echo offline > /sys/devices/system/memory/memory136/state # echo online_movable > /sys/devices/system/memory/memory136/state # ./hmm-swap & ... wait until everything is device-exclusive # echo offline > /sys/devices/system/memory/memory136/state [ 285.193431][T14882] page: refcount:2 mapcount:0 mapping:0000000000000000 index:0x7f20671f7 pfn:0x442b6a [ 285.196618][T14882] memcg:ffff888179298000 [ 285.198085][T14882] anon flags: 0x5fff0000002091c(referenced|uptodate| dirty|active|owner_2|swapbacked|node=1|zone=3|lastcpupid=0x7ff) [ 285.201734][T14882] raw: ... [ 285.204464][T14882] raw: ... [ 285.207196][T14882] page dumped because: migration failure [ 285.209072][T14882] page_owner tracks the page as allocated [ 285.210915][T14882] page last allocated via order 0, migratetype Movable,...