[PATCH] D41723: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715, "Branch Target Injection", and is one of the two halves to Spectre..

[Chandler Carruth via Phabricator via llvm-commits]

chandlerc added a comment.

In https://reviews.llvm.org/D41723#976776, @jyknight wrote:

> Per kernel https://marc.info/?l=linux-kernel&m=151580566622935&w=2 and gcc https://gcc.gnu.org/ml/gcc-patches/2018-01/msg01059.html, it seems AMD needs there to be an lfence in the speculation trap (and the pause is not useful for them, but does no harm). There seems to be some speculation (but no confirmation yet?) that pause *is* necessary vs lfence on intel. So in order to work generically, they seem to be suggesting using both instructions:
>
>   loop:
>     pause
>     lfence
>     jmp loop
>
>
> Some more links
>  https://gcc.gnu.org/ml/gcc-patches/2018-01/msg01209.html
>  and final patch:
>  https://github.com/gcc-mirror/gcc/commit/a31e654fa107be968b802786d747e962c2fcdb2b


Thanks for digging all of this up, but I have to say that it would be really awesome of folks from AMD would actually comment on this thread and/or patch rather than us relaying things 2nd and 3rd hand....

I'll look at implementing this, but I'm not super thrilled to change so much of the code at this point. The code as-is is secure, and merely power-inefficient on AMD chips. I'd like to fix that, but if it creates problems in testing, I'm inclined to wait for AMD to actually join the discussion.


Repository:
  rL LLVM

https://reviews.llvm.org/D41723