CVE-2025-37958 Information

Description

In the Linux kernel the following vulnerability has been resolved:

mm/huge_memory: fix dereferencing invalid pmd migration entry

When migrating a THP concurrent access to the PMD migration entry during a deferred split scan can lead to an invalid address access as illustrated below. To prevent this invalid access it is necessary to check the PMD migration entry and return early. In this context there is no need to use pmd_to_swp_entry and pfn_swap_entry_to_page to verify the equality of the target folio. Since the PMD migration entry is locked it cannot be served as the target.

Mailing list discussion and explanation from Hugh Dickins: \An anon_vma lookup points to a location which may contain the folio of interest but might instead contain another folio: and weeding out those other folios is precisely what the olio != pmd_folio((pmd)\ check (and the isk of replacing the wrong folio\ comment a few lines above it) is for.\n BUG: unable to handle page fault for address: ffffea60001db008 CPU: 0 UID: 0 PID: 2199114 Comm: tee Not tainted 6.14.0+ 4 NONE Hardware name: QEMU Standard PC (Q35 + ICH9 2009) BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:split_huge_pmd_locked+0x3b5/0x2b60 Call Trace: try_to_migrate_one+0x28c/0x3730 rmap_walk_anon+0x4f6/0x770 unmap_folio+0x196/0x1f0 split_huge_page_to_list_to_order+0x9f6/0x1560 deferred_split_scan+0xac5/0x12a0 shrinker_debugfs_scan_write+0x376/0x470 full_proxy_write+0x15c/0x220 vfs_write+0x2fc/0xcb0 ksys_write+0x146/0x250 do_syscall_64+0x6a/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e

The bug is found by syzkaller on an internal kernel then confirmed on upstream.

Reference

https://git.kernel.org/stable/c/6166c3cf405441f7147b322980144feb3cefc617 https://git.kernel.org/stable/c/be6e843fc51a584672dfd9c4a6a24c8cb81d5fb7 https://git.kernel.org/stable/c/fbab262b0c8226c697af1851a424896ed47dedcc