Disable SMT/Hyperthreading in all Intel BIOSes

Post by Roritharr » Thu, Aug 23, 2018, 7:53 PM UTC

geofft wrote: post #37

Roritharr wrote: post #32

Earlier quoted context omitted.

The latter question is very important indeed. If you for instance render websites in your vm they, if i understand correctly, can potentially read secrets from other processes, like db credentials and other stuff... If the only real solution is to turn off HT/SMT that, seen positively, should net us a lot faster VMs then...

If you render websites that run code in your VM (e.g., you're running a traditional shared hosting infrastructure where mutually-untrusted users can upload PHP scripts, or you're doing something serverless / FaaS / Cloudflare Workers / etc. where mutually-untrusted users can upload functions), then yes. If you're rendering websites in the sense of hosting WordPress for lots of people but not permitting custom plugins…

Post by ysleepy » Thu, Aug 23, 2018, 7:53 PM UTC

geofft wrote: post #33

> SMT is fundamentally broken because it shares resources between the two cpu instances and those shared resources lack security differentiators. I thought the root of one of the Foreshadow problems was that caches are shared across cores , and therefore even with hyperthreading disabled, you still gain information about a process on another core. Am I misinterpreting it? It does seem like the paranoid thing to do is…

Post by vorpalhex » Thu, Aug 23, 2018, 7:55 PM UTC

fermienrico wrote: post #17

ofrzeta wrote: post #11

Earlier quoted context omitted.

That would be hard to market.

Indeed, the idea of "Security" is not negotiable when marketing. Imagine buying a car that says, "Save $5000 for a less safe version without airbags." Yes, I know Airbags are DOT requirement, just trying to make a point. Edit: I think people are missing my point. I am not saying they don't sell cheaper models that are less safe. My point is that they don't ACTIVELY market them as such. Point me to an advertisement th…

Post by wmf » Thu, Aug 23, 2018, 7:56 PM UTC

fermienrico wrote: post #4

Roritharr wrote: post #2

Does that mean hyperthreading is effectively unpatchably insecure? Cloud Providers are gonna have a bad time if this is true.

Question: If I rent 4 core AWS instance, does it mean 4 physical cores or 4 hyper threaded cores? Is there a standard to this definition of “cores” across GCP, DO, Linode, etc. I don’t have the experience or knowledge about cloud computing but just have a DO instance running a web server. I’m curious.

Post by gruez » Thu, Aug 23, 2018, 8:00 PM UTC

Roritharr wrote: post #32

geofft wrote: post #22

Earlier quoted context omitted.

You can give both hyperthreads in a physical core to the same tenant, no? Scheduling different VMs to run on the same hyperthreaded core at once seems like it can't be good for either VM's performance, even if there were no security concerns. Hyperthreading is much more useful for running multiple threads of the same app, accessing similar instruction caches etc. (There's also a question of safety within the VM, but…

The latter question is very important indeed. If you for instance render websites in your vm they, if i understand correctly, can potentially read secrets from other processes, like db credentials and other stuff... If the only real solution is to turn off HT/SMT that, seen positively, should net us a lot faster VMs then...