Linux KVM - PV TLB shootdown leaks memory between guest processes: MULTI-TENANT ISOLATION: In a KVM guest

Impact

MULTI-TENANT ISOLATION: In a KVM guest with paravirtualised TLB enabled, one process in the guest can read memory belonging to another process in the same guest. The isolation that breaks is inside the VM rather than between VMs - which matters for any operator whose customers run multi-user workloads inside a single VM, and for confidential guests where the tenant assumed process separation held.

Who can reach it

Local, from one process to another inside a KVM guest with PV TLB enabled. The host must be running Linux with KVM.

What to do

Fixed in the Linux kernel. The fix belongs in the **guest** kernel, so update confidential and tenant VM images, not just hosts. Interim mitigation: disable PV TLB flush in the guest (the kvm.pv_tlb boot option / KVM_FEATURE_PV_TLB_FLUSH), which costs some scheduling efficiency and needs a guest reboot.

References