Linux Kernel CVE-2025-68179

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

s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP

As reported by Luiz Capitulino enabling HVO on s390 leads to reproducible crashes. The problem is that kernel page tables are modified without flushing corresponding TLB entries.

Even if it looks like the empty flush_tlb_all() implementation on s390 is the problem, it is actually a different problem: on s390 it is not allowed to replace an active/valid page table entry with another valid page table entry without the detour over an invalid entry. A direct replacement may lead to random crashes and/or data corruption.

In order to invalidate an entry special instructions have to be used (e.g. ipte or idte). Alternatively there are also special instructions available which allow to replace a valid entry with a different valid entry (e.g. crdte or cspg).

Given that the HVO code currently does not provide the hooks to allow for an implementation which is compliant with the s390 architecture requirements, disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP again, which is basically a revert of the original patch which enabled it.

The affected product is the Linux kernel on the s390/s390x (IBM Z mainframe) architecture, in versions where ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP (HVO) was enabled for s390. No CPE strings or explicit version ranges were provided in the input, so the exact vulnerable range cannot be enumerated with certainty; the fix is distributed across the stable trees referenced at git.kernel.org (commits 5e23918e4352288323d13fb511116cdea0234b71, 64e2f60f355e556337fcffe80b9bcff1b22c9c42, 7088465f10816d9425b95740b37c95f082041d76, and d4a8238e5729505b7394ccb007e5dc3e557aa66b), indicating multiple stable branches received the backport.