PT-2026-61258 · Linux · Linux
CVE-2026-63941
·
Published
2026-07-19
·
Updated
2026-07-19
CVSS v3.1
8.8
High
| Vector | AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |
In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: Correctly cap ZCR EL2 provided by a guest hypervisor
ZCR EL2 can be updated by a VHE guest hypervisor either using ZCR EL2
(which traps) or ZCR EL1 (which does not trap). KVM handles both in
different way:
-
on ZCR EL2 trap, ZCR EL2.LEN is immediately capped at the VM's own VL limit. This has the potential to break existing SW that relies on the full LEN field to be stateful.
-
on ZCR EL1 access, we do absolutely nothing.
On restoring the SVE context for an L2 guest, we directly restore the
guest hypervisor's view of ZCR EL2 into the physical ZCR EL2. If the
guest's view of the register was updated using the ZCR EL2 accessor,
the value has already been sanitised (with the caveat mentioned above).
But if the guest used ZCR EL1, the raw value is written into the HW,
and the L2 guest can now access VLs that it shouldn't.
Fix all the above by moving the VL capping to the restore points,
ensuring that:
-
the HW is always programmed with a capped value, irrespective of the accessor being used,
-
the ZCR EL2.LEN field is always completely stateful, irrespective of the accessor being used.
Additionally, move ZCR EL2 to be a sanitised register, ensuring that
only the LEN field is actually stateful. This requires some creative
construction of the RES0 mask, as the sysreg generation script does
not yet generate RAZ/WI fields.
[maz: rewrote commit message, tidy up access zcr el2()]
Fix
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Related Identifiers
Affected Products
Linux