[GTALUG] more on Spectre v2

[David Collier-Brown]

On 04/02/18 01:29 PM, D. Hugh Redelmeier via talk wrote:
> Spectre v2 is really complicated to deal with.  Just read this
> recent thread in the LKML
> <https://lkml.org/lkml/2018/1/20/158>
> I'm impressed how well written those messages are.
>
> Intel Skylake CPUs are particularly problematic.  Those are most of the
> "6th generation Core" processors and some of the "7th generation Core".
> <https://en.wikipedia.org/wiki/Skylake_(microarchitecture)>
>
> The indirect branch predictor is a big problem.  The retpoline deals with
> most cases.  On Skylake, this predictor is used in another case: for
> return instructions that cause underflow in the call/return predictor
> stack.
There's also a race condition: the 6130 and DPS8m processors checked the
permissions of the fetch before they fetched to the (then small) cache.

Simulating the same thing in the Multics emulator took some extra work but
it was implemented well before the spectre attacks showed up.

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain