Linux KVM - SEV-ES/SEV-SNP VMGEXIT double-fetch race: A KVM guest running SEV-ES or SEV-SNP with several vCPUs can

Impact

A KVM guest running SEV-ES or SEV-SNP with several vCPUs can trigger a double-fetch race in the host's VMGEXIT handler and drive it into recursion. Repeated invocation exhausts the host kernel stack and panics the hypervisor - a confidential guest taking down the host it runs on, and with it every other tenant on that machine. This is guest-to-host denial of service, which is the direction operators care about.

Who can reach it

From inside a guest VM using SEV-ES or SEV-SNP with multiple vCPUs. Tenant-reachable - no host privilege needed.

What to do

Fixed in the Linux kernel - KVM/x86 SEV code or the ccp/PSP driver. Take the distro kernel update (RHEL/Rocky, Ubuntu, SLES) and **reboot the host**; SEV/SNP hypervisor paths cannot be live-patched in any meaningful way, and SNP platform init/shutdown is not safe to cycle under running guests. Drain confidential-VM tenants, reboot, then re-admit. No firmware, VBIOS or AGESA step needed, which makes this one of the cheaper classes of SEV fix to roll out. Prioritise on any host that admits tenant-controlled confidential VMs; the attacker prerequisite is just 'has a VM here'.

References