CVE-2026-89908: Linux Vulnerability (CVSS 8.8)

Description

In the Linux kernel, the following vulnerability has been resolved: LoongArch: KVM: Preserve memslot arch flags on KVM_MR_FLAGS_ONLY kvm_arch_prepare_memory_region() computes new->arch.flags, i.e. whether a memslot is KVM_MEM_HUGEPAGE_CAPABLE or KVM_MEM_HUGEPAGE_INCAPABLE, only for KVM_MR_CREATE and KVM_MR_MOVE, and returns early for every other change. But the generic code allocates a zeroed memslot for every change and never copies old->arch, so after a KVM_MR_FLAGS_ONLY update, e.g. toggling KVM_MEM_LOG_DIRTY_PAGES for live migration, the active memslot has arch.flags == 0. With both flags clear, fault_supports_huge_mapping() falls through to the alignment check on the HVA range alone, which no longer verifies that the GPA and HVA have the same offset within a PMD. A memslot that was marked KVM_MEM_HUGEPAGE_INCAPABLE because of a GPA/HVA offset mismatch can then be mapped with PMD entries on read faults, and since kvm_map_page() aligns the gfn and the pfn independently, the guest ends up accessing the wrong host pages, exactly the "d -> f, e -> g" case described in the comment above the check. Carry the arch flags over from the old memslot for KVM_MR_FLAGS_ONLY, as the GPA, HVA and size are guaranteed to be unchanged for that case.

Metrics

CVSS 3.1

8.8/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 7ab6fb505b2a7447c4a7237a12c59e3ad0c7298c, < 7c6df65b53846cd7a9a1c81c6ddb42fdc08603e8; >= 7ab6fb505b2a7447c4a7237a12c59e3ad0c7298c, < 4e4dbc341b1581dc512b85d98b768373b0398366; >= 7ab6fb505b2a7447c4a7237a12c59e3ad0c7298c, < bc7a6849b4395f45a602db91b0fb2fb2e9ed4bba; >= 7ab6fb505b2a7447c4a7237a12c59e3ad0c7298c, < 27a9bfee3bbcb3cabb77797354f07e0e44e49831
Linux	Linux	6.8

References

Timeline

Published: Sep 16, 2026
Last Modified: Sep 16, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89908?

In the Linux kernel, the following vulnerability has been resolved: LoongArch: KVM: Preserve memslot arch flags on KVM_MR_FLAGS_ONLY kvm_arch_prepare_memory_region() computes new->arch.flags, i.e. whether a memslot is KVM_MEM_HUGEPAGE_CAPABLE or KVM_MEM_HUGEPAGE_INCAPABLE, only for KVM_MR_CREATE and KVM_MR_MOVE, and returns early for every other change. But the generic code allocates a zeroed memslot for every change and never copies old->arch, so after a KVM_MR_FLAGS_ONLY update, e.g. toggling KVM_MEM_LOG_DIRTY_PAGES for live migration, the active memslot has arch.flags == 0. With both flags clear, fault_supports_huge_mapping() falls through to the alignment check on the HVA range alone, which no longer verifies that the GPA and HVA have the same offset within a PMD. A memslot that was marked KVM_MEM_HUGEPAGE_INCAPABLE because of a GPA/HVA offset mismatch can then be mapped with PMD entries on read faults, and since kvm_map_page() aligns the gfn and the pfn independently, the guest ends up accessing the wrong host pages, exactly the "d -> f, e -> g" case described in the comment above the check. Carry the arch flags over from the old memslot for KVM_MR_FLAGS_ONLY, as the GPA, HVA and size are guaranteed to be unchanged for that case.

How severe is CVE-2026-89908?

CVE-2026-89908 has a CVSS score of 8.8/10 (HIGH severity).

How do I fix CVE-2026-89908?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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