Spectre mitigation

Fri Jan 5 21:49:03 UTC 2018

> 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 <carter.schonwald at gmail.com> 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 <eacameron at gmail.com> wrote:
>
>> 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 at gmail.com> wrote:
>>
>>> 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 <tjakway at nyu.edu> wrote:
>>>
>>>> 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" <carter.schonwald at gmail.com>
>>>> wrote:
>>>>
>>>>> 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 <demiobenour at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> 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 at haskell.org
>>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> ghc-devs mailing list
>>>>> ghc-devs at haskell.org
>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>>>>>
>>>>>
>>> _______________________________________________
>>> ghc-devs mailing list
>>> ghc-devs at haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>>>
>>>
>> _______________________________________________
> ghc-devs mailing list
> ghc-devs at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20180105/0eec7090/attachment-0001.html>