Bug 2375304 (CVE-2025-38085)

Summary: CVE-2025-38085 kernel: mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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OS: Linux   
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Description OSIDB Bzimport 2025-06-28 08:01:11 UTC 
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.
Comment 1 Avinash Hanwate 2025-06-30 02:54:28 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025062836-CVE-2025-38085-8075@gregkh/T