[PATCH] D80964: [X86] Add an Unoptimized Load Value Injection (LVI) Load Hardening Pass

[Scott Constable via Phabricator via llvm-commits]

sconstab added a comment.

In D80964#2077614 <https://reviews.llvm.org/D80964#2077614>, @mattdr wrote:

> Isn't this pass basically SESES? https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86SpeculativeExecutionSideEffectSuppression.cpp
>
> Perhaps there's an opportunity to unify the two.


My understanding of SESES is that it inserts an `LFENCE` before each transmitter, whereas this pass inserts an `LFENCE` after each load. They are slightly different threat models; SESES is more strict. For example, SESES would mitigate the following vulnerability, whereas the LVI hardening will not:

  uint64_t maybe_secret = *ptr;                           // architectural load
  __mm_lfence();
  if (is_secret) {                                        // suppose `is_secret == true` but branch mispredicts
      // do something constant-time with `maybe_secret`
  } else {
      return byte_array[maybe_secret * 4096];             // speculatively leak the secret
  }

I'm not opposed to merging the two approaches. But I am also not sure how to justify it.


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