CVE-2026-63875: arm64: tlb: Flush walk cache when unsharing PMD tables
In the Linux kernel, the following vulnerability has been resolved:
arm64: tlb: Flush walk cache when unsharing PMD tables
When hugepmdunshare() is called to unshare a PMD table, the tlbunsharepmdptdesc() function sets tlb->unsharedtables=true but the aarch64 tlbflush() only checked tlb->freedtables to determine whether to use TLBFNONE (vae1is, invalidates walk cache) or TLBFNOWALKCACHE (vale1is, leaf-only).
This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks.
Fix by including unsharedtables in the check, so that when unsharing tables, TLBFNONE is used and the walk cache is properly invalidated.
Here is the detailed distinction between vae1is and vale1is:
| Instruction Combination | Actual Invalidation Scope | | ------------------------ | --------------------------------------------------| | VAE1IS + TTL=0 | All entries at all levels (full invalidation) | | VAE1IS + TTL=2 (L2) | Non-leaf at Level 0/1 + leaf at Level 2 | | VALE1IS + TTL=0 | Leaf entries at all levels (non-leaf not cleared) | | VALE1IS + TTL=2 (L2) | Leaf entry at Level 2 only |
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-azure-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1123.132~20.04.1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1123.132+fips1 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1011.11~24.04.1 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1065.73 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-28.28~24.04.1 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1066.67 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1064.67 - Upgrade
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ubuntu/linux-nvidia-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.16~24.04.1 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 6.8.0-1063.66 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1011.11~24.04.1 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1003.4 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1008.8 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.176-1 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.176-1Fixed in 6.1.190-1Fixed in 6.12.107-1Fixed in 6.12.113-1Fixed in 7.2.12-1Fixed in 7.2.14-1 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 5.10.259 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 5.15.210 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.6.143 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.18.35 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 7.0.12 - Configuration
Update aarch64 tlb_flush() so that unsharing PMD tables causes TLBF_NONE (VAE1IS) to be used, invalidating the walk cache and preventing stale PMD entries after unshare.
Linux kernel arm64 TLB handling aarch64 tlb_flush() TLBF_NONE selection condition = Include tlb->unshared_tables in the check alongside tlb->freed_tables
Event History
Frequently Asked Questions
Which systems are exposed?
The issue applies to arm64 Linux kernel systems. The affected software list includes Linux kernel packages and several Ubuntu kernel variants, including linux-realtime, linux-azure, linux-gcp, linux-azure-fde, linux-gke, and linux-riscv.
What access or conditions are required for exploitation?
The supplied vector indicates local access, low privileges, and no user interaction are required. The fault occurs when a PMD table is unshared through huge_pmd_unshare(), leaving a stale PMD entry in the walk cache.
What is the practical effect of the flaw?
A stale PMD page-table entry can remain in the arm64 walk cache after a PMD table is unshared. This can cause incorrect page-table walks and is rated as having high confidentiality, integrity, and availability impact in the supplied vector.
How can I verify that a kernel contains the fix?
The correction changes arm64 TLB flushing so that unshared_tables, as well as freed_tables, selects a flush that invalidates the walk cache. The provided stable-kernel references are commits dced308d7d6a0de1c09d2058f38f1aaaf5cbb914, 47490bbb05c8c0e09cc3cfd237d8934ffc340583, and 0199c9d57861f17b556b6cba1f765c7cce79745b.