Device Register Partial Write (DRPW)

A low-privileged authenticated local attacker may disclose sensitive data available through stale fill-buffer contents. The assessed impact is high confidentiality loss, with no direct integrity or availability impact. In virtualized environments, exposure may affect security boundaries where an untrusted guest has direct MMIO access. Stale data propagated into fill buffers may also be inferable through otherwise-unmitigated MDS, MFBDS, or TAA techniques.

Limit or prevent direct MMIO access by untrusted software, particularly untrusted virtual-machine guests. Where an untrusted guest can access MMIO and the processor is not affected by MDS or TAA, execute the applicable VERW-based fill-buffer clearing before VMENTER. Where MDS or TAA is relevant, clear fill buffers before transitions to untrusted software according to the corresponding MDS mitigations. Avoid co-scheduling distinct security domains on SMT sibling threads, or use core scheduling/isolation, to reduce race-based extraction and confused-deputy exposure. No standalone general mitigation was identified for deployments unable to apply the necessary firmware and software updates.

Apply the applicable Intel microcode or platform firmware update together with supported operating-system and VMM updates that implement Processor MMIO Stale Data mitigations. On systems supporting FB_CLEAR, the memory-operand form of VERW is used to clear fill buffers; deploy kernels and hypervisors that invoke this mitigation at the required privilege and virtualization transitions. For Red Hat Enterprise Linux, install the applicable vendor-provided kernel or kernel-rt erratum for the deployed product stream and reboot so the updated kernel and microcode mitigations take effect.