Shared Buffers Data Sampling (SBDS)

A locally authenticated, low-privileged attacker can disclose confidential data processed in affected microarchitectural buffers. The assessed impact is high confidentiality impact, with no integrity or availability impact. In virtualized deployments, exposure is especially relevant where untrusted guests receive direct MMIO-capable device access; stale data propagated into a fill buffer may be recoverable across a security boundary. SMT can introduce timing races that increase extraction and confused-deputy leakage risk.

Restrict direct MMIO access by untrusted software and untrusted virtual-machine guests. Where MDS or TAA is also present, clear fill buffers with VERW before transitions to untrusted software in accordance with MDS mitigations. On systems not affected by MDS or TAA, execute VERW before VMENTER when an untrusted guest can access MMIO. Avoid co-scheduling mutually untrusted workloads on sibling SMT threads, or use core scheduling/isolation; disabling SMT may be necessary where suitable scheduling isolation cannot be assured. Verify processor mitigation capability and status through the relevant architectural capability reporting, including FB_CLEAR support.

Apply Intel-provided microcode or system firmware updates and the corresponding operating-system and VMM updates that implement Processor MMIO Stale Data mitigations. On supported processors, software should use the memory-operand form of VERW to clear fill buffers where required; the register-operand form is not suitable for this purpose. Install vendor kernel updates containing the mitigation and reboot to activate the new kernel and microcode state. For Red Hat Enterprise Linux, use the applicable fixed kernel or kernel-rt packages for the deployed product stream rather than relying on upstream version comparisons, because fixes may be backported.