Intel's "redundant prefix issue"

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

We believe this bug causes the frontend to miscalculate the size of
the movsb instruction, causing subsequent entries in the ROB [reorder buffer] to be
associated with incorrect addresses. When this happens, the CPU
enters a confused state that causes the instruction pointer to be
miscalculated.

The machine can eventually recover from this state, perhaps with
incorrect intermediate results, but becoming internally consistent
again. However, if we cause multiple SMT or SMP cores to enter the
state simultaneously, we can cause enough microarchitectural state
corruption to force a machine check.

Intel has released
a microcode update to address the issue.