  Existing speculative execution attacks are limited to breaching
confidentiality of data beyond privilege boundary, the so-called spectre-type
attacks. All of them utilize the changes in microarchitectural buffers made by
the speculative execution to leak data. We show that the speculative execution
can be abused to break data integrity. We observe that the speculative
execution not only leaves traces in the microarchitectural buffers but also
induces side effects within DRAM, that is, the speculative execution can
trigger an access to an illegitimate address in DRAM. If the access to DRAM is
frequent enough, then architectural changes (i.e., permanent bit flips in DRAM)
will occur, which we term GhostKnight. With the power of of GhostKnight, an
attacker is essentially able to cross different privilege boundaries and write
exploitable bits to other privilege domains. In our future work, we will
develop a GhostKnight-based exploit to cross a trusted execution environment,
defeat a 1024-bit RSA exponentiation implementation and obtain a controllable
signature.
