CVE-2025-38085: mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-06-28 · updated 2026-07-30
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race huge_pmd_unshare() drops a reference on a page table that may have previously been shared across processes, potentially turning it into a normal page table used in another process in which unrelated VMAs can afterwards be installed. If this happens in the middle of a concurrent gup_fast(), gup_fast() could end up walking the page tables of another process. While I don't see any way in which that immediately leads to kernel memory corruption, it is really weird and unexpected. Fix it with an explicit broadcast IPI through tlb_remove_table_sync_one(), just like we do in khugepaged when removing page tables for a THP collapse.

Affected products

Debian Linux: 11.0
Linux kernel: from 2.6.20 before 5.10.239; from 5.11 before 5.15.186; from 5.16 before 6.1.142; from 6.2 before 6.6.95; from 6.7 before 6.12.35; from 6.13 before 6.15.4 — fixed in 5.10.239, 5.15.186, 6.1.142, 6.12.35, 6.15.4, 6.6.95

How to fix

Upgrade to a fixed version: Linux kernel 5.10.239, 5.15.186, 6.1.142, 6.12.35. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-38085 or the next vulnerability affects your stack