[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 llvm-commits llvm-commits at lists.llvm.org
Thu Jan 4 08:40:23 PST 2018

Replying via email as Phab is ... sad still.

On Thu, Jan 4, 2018 at 9:55 AM Tom Stellard via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:

> tstellar added a comment.
> Does this CVE affect all previous versions of clang/llvm ?

It's orthogonal. The CVE is a hardware issue. This patch allows specific,
sensitive software systems to mitigate this CVE with a new suite of
compiler features.

So the CVE doesn't affect any particular version, but everyone *is*
affected and we should try to get this feature into all mainstream versions
of clang/llvm to help users mitigate it.

> The Project Zero blog post mention that this issue affects ARM CPUs, does
> clang/llvm need a similar fix for ARM?

Perhaps, but it will need to be reasonably tailored to ARM processors. The
technique of using a "ret" as a constrained prediction domain indirect
branch is a pretty x86-specific trick.

All the other components are generic and should be easily adapted to other
processors if they need them.

> Is this fix important enough to do a special 5.0.2 release for it?

IMO, absolutely. I'd love to get this landed, backported, and a 5.0.2
release out within O(days) because that way distros can pick it up rapidly.

I view this as relatively low risk as it is an entirely optional code path.
It may have bugs, but it shouldn't make existing things buggy.

> https://reviews.llvm.org/D41723
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