CVE-2024-35980: arm64: tlb: Fix TLBI RANGE operand
In the Linux kernel, the following vulnerability has been resolved:
arm64: tlb: Fix TLBI RANGE operand
KVM/arm64 relies on TLBI RANGE feature to flush TLBs when the dirty
pages are collected by VMM and the page table entries become write
protected during live migration. Unfortunately, the operand passed
to the TLBI RANGE instruction isn't correctly sorted out due to the
commit 117940aa6e5f ("KVM: arm64: Define kvm_tlb_flush_vmid_range()").
It leads to crash on the destination VM after live migration because
TLBs aren't flushed completely and some of the dirty pages are missed.
For example, I have a VM where 8GB memory is assigned, starting from
0x40000000 (1GB). Note that the host has 4KB as the base page size.
In the middile of migration, kvm_tlb_flush_vmid_range() is executed
to flush TLBs. It passes MAX_TLBI_RANGE_PAGES as the argument to
__kvm_tlb_flush_vmid_range() and __flush_s2_tlb_range_op(). SCALE#3
and NUM#31, corresponding to MAX_TLBI_RANGE_PAGES, isn't supported
by __TLBI_RANGE_NUM(). In this specific case, -1 has been returned
from __TLBI_RANGE_NUM() for SCALE#3/2/1/0 and rejected by the loop
in the __flush_tlb_range_op() until the variable @scale underflows
and becomes -9, 0xffff708000040000 is set as the operand. The operand
is wrong since it's sorted out by __TLBI_VADDR_RANGE() according to
invalid @scale and @num.
Fix it by extending __TLBI_RANGE_NUM() to support the combination of
SCALE#3 and NUM#31. With the changes, [-1 31] instead of [-1 30] can
be returned from the macro, meaning the TLBs for 0x200000 pages in the
above example can be flushed in one shoot with SCALE#3 and NUM#31. The
macro TLBI_RANGE_MASK is dropped since no one uses it any more. The
comments are also adjusted accordingly.
Security readout for executives and security teams
Plain-English summary
A Linux kernel flaw on Arm64 KVM hosts can leave stale memory translations after pages are write-protected during virtual-machine live migration. The incomplete flush may cause the migrated VM to crash at its destination and may compromise memory integrity. The supplied CVSS score is 8.4, making this a high-priority reliability and isolation concern for affected virtualization environments.
Executive priority
Treat as high priority for organizations operating Arm64 KVM live migration, especially where VM availability or workload integrity is business-critical. Inventory exposed hosts promptly and schedule verified kernel updates. Organizations without this architecture and migration workflow should document non-exposure rather than launch an emergency patch cycle solely for this CVE.
Technical view
An invalid TLBI RANGE operand can be generated because the range-number calculation did not support SCALE 3 with NUM 31. The scale variable may underflow, producing an incorrect operand and an incomplete stage-2 TLB flush. Dirty pages can consequently be missed during KVM/arm64 live migration, causing destination-VM crashes. The cited kernel commits extend the calculation to support the missing combination.
Likely exposure
Exposure is limited to affected Linux kernels on Arm64 systems using KVM and the TLBI RANGE feature, particularly where VMs undergo live migration. Systems without Arm64 KVM, TLBI RANGE, or live migration are less likely to encounter the documented failure path. The supplied version data identifies affected 6.6 through 6.9-era entries but is not sufficiently precise for every distribution build.
Exploitation context
The CVSS vector describes local access, low complexity, low privileges, no user interaction, changed scope, and high integrity and availability impact without confidentiality impact. The documented outcome is a destination-VM crash after live migration. The bundle marks the CVE as absent from KEV and provides no cited evidence of active exploitation; that does not prove exploitation has never occurred.
Researcher notes
The central defect is operand construction for the maximum TLBI range: SCALE 3 and NUM 31 was unsupported, allowing scale underflow and an invalid address-range operand. The fix permits that combination and removes an unused mask. The bundle does not identify a CWE, public exploit, or exact distribution package mapping, so validation should rely on vendor backport records and the cited commits.
Mitigation direction
Identify Arm64 KVM hosts running the affected kernel lines and prioritize those supporting live migration.
Apply the appropriate vendor kernel update containing the cited TLBI RANGE correction.
Confirm distribution backport status because package versions may not match upstream kernel numbering.
Consider temporarily restricting live migration on unpatched affected hosts after evaluating operational impact.
Validation and detection
Record kernel and distribution package versions across all Arm64 KVM hosts.
Check vendor advisories or package changelogs for a backport of the cited correction.
Verify whether Arm64 hosts expose TLBI RANGE and perform KVM live migration.
After updating, perform controlled migration testing and monitor destination VMs for crashes or integrity failures.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Potential ATT&CK relevance
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