Re: Spectre mitigation

The only impacted code is the code which should already be engineered to be side channel resistant... which already need to be written in a way that has constant control flow and memory lookup.

As far as I understand, that's not really true. If you have a process, which has secrets that you do not want to leak to arbitrary other code running on the same CPU, then not only do you need to avoid indirect branches in your side-channel resistent part (as is the case today) but the *rest* of the program also should not contain indirect branches (assuming the presence of gadgets which make memory leaking possible). So even if your crypto library uses no indirect branches and is side-channel resistant, that is no longer enough: if you link it into a program where other parts of the program have indirect branches, then you can use those branches to potentially leak the crypto keys. So in general, you need to apply mitigations for this attack if you, at any time, store secrets in the process memory that you do not want to be leaked (and being a hardware bug, leaking means that they can, potentially, be leaked to arbitrary users. Privilege-separation provided by the OS does not really matter here, so in theory it may be possible to leak it from JavaScript running in a browser sandbox for example.). Carter Schonwald schrieb am Fr., 5. Jan. 2018 um 00:07 Uhr:

Indeed. It’s worth noting that the discussed cases where you can recover the perf benefits of branch / jump prediction only work in the context of a first order and or whole program compilation approach. The ghc rts and design is not compatible with those approaches today.

I suspect you could get them to work in a whole program optimizing compiler like MLTON, or a hypothetical compiler for Haskell that has a different rts rep

On Thu, Jan 4, 2018 at 4:25 PM Elliot Cameron wrote:

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This may be relevant: https://support.google.com/faqs/answer/7625886

Note that both GCC and LLVM will be learning this Ratpoline technique.

On Thu, Jan 4, 2018 at 1:55 PM, Carter Schonwald < carter.schonwald@gmail.com> wrote:

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With the caveat of that I maybe have no clue what I’m talking about ;) :

It’s a pretty epic attack/ side channel, but it still requires code execution.

The kernel side channel more of an issue for vm providers

And the spectre one probably will most heavily impact security conscious organizations that might be considering using tools like moby/ docker / Linux containers / kubernetes / mesos/ etc which depend on OS level process isolation etc for security.

My fuzzy understanding is that one fix would be hardware support for per process isolation of memory even in the context users / processes ... which isn’t in any kit afaik.

I do like my code not being slow. So it’s a dilemma :/

On Thu, Jan 4, 2018 at 11:51 AM Thomas Jakway wrote:

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I'm gonna start reading through the spectre paper in a few minutes but... is this really the death knell for speculative execution on x86/64...? If so, GHC getting patched is going to be pretty low on everyone's list of priorities.

On Jan 4, 2018 6:36 AM, "Carter Schonwald" wrote:

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The only impacted code is the code which should already be engineered to be side channel resistant... which already need to be written in a way that has constant control flow and memory lookup.

This is just a new and very powerful side channel attack. It would be interesting and possibly useful to explore fascilities that enable marked pieces of code to be compiled in ways that improve side channel resistance. But there’s so many different approaches that it’d be difficult to protect against all of them at once for general programs.

I could be totally wrong, and I should read the spectre paper :)

I guess I just mean that vulnerable Data should be hardened, but only when the cost makes sense. Every security issue has some finite cost. The sum of those security events cost must be weighed against the sum of the costs of preventing them

On Thu, Jan 4, 2018 at 9:08 AM Demi Obenour wrote:

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The recent “Spectre” bug requires that speculative execution of indirect branches be disabled. For GHC, this will require passing a flag to LLVM and fixing the NCG to emit suitable calling sequences.

This will be a disaster for the STG execution model, because it disables CPU branch prediction for indirect calls and jumps. This is a big argument in favor of doing a CPS→SSA conversion in the backend. _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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