Intel's "redundant prefix issue"

Tavis Ormandy has described a bugin some Intel CPUs that can lead to a crash (or worse):

We believe this bug causes the frontend to miscalculate the size ofthe movsb instruction, causing subsequent entries in the ROB [reorder buffer] to beassociated with incorrect addresses. When this happens, the CPUenters a confused state that causes the instruction pointer to bemiscalculated.

The machine can eventually recover from this state, perhaps withincorrect intermediate results, but becoming internally consistentagain. However, if we cause multiple SMT or SMP cores to enter thestate simultaneously, we can cause enough microarchitectural statecorruption to force a machine check.

Intel has releaseda microcode update to address the issue.