In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Apply the fine-grained UNDEFs without FEAT_FGT FGUs don't actually… (CVE-2026-98713)

The vulnerability in the Linux kernel KVM arm64 subsystem involved the application of fine-grained undefined instruction traps (UNDEFs) without checking for the FEAT_FGT hardware feature. FGUs do not require hardware support, but the kernel incorrectly gated the insertion of fine-grained trap configuration on FEAT_FGT presence. This caused spurious warnings when a TLBI OS was run on a guest in vEL1 without FEAT_TLBIOS on hardware lacking FEAT_FGT, due to improper trap handling. The patch removes this gating, allowing FGUs always, as the trap bits are computed correctly regardless of FEAT_FGT. This resolves the issue and prevents the spurious WARN and incorrect trap handling.

The vulnerability could cause spurious warnings and improper trap handling in virtualized environments running on arm64 hardware without FEAT_FGT support. This may affect the stability or correctness of KVM virtualization but does not indicate direct exploitation or security compromise. No known exploits are reported in the wild.

A fix for this vulnerability has been applied in the Linux kernel. Users should update to the kernel version containing this patch to resolve the issue. No additional mitigation actions are required beyond applying the official fix.