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A new thing that's going to become a standard part of systems engineering: deciding whether any given system needs to run with or without these kinds of protect
by jzl 9y ago
A new thing that's going to become a standard part of systems engineering: deciding whether any given system needs to run with or without these kinds of protections. Do you want the speed of speculative execution or do you want Meltdown/Spectre protection? In some cases lack of protection is fine. But figuring out the answer for any given system is often going to take expert-level security knowledge. Security is all about multiple layers of protection, and even a non-public facing machine might benefit from these layers depending on the context.
- crb002 9y agoCPUs should have a single instruction that wipes branch prediction caches. I would have it off by default, and add to the C/C++ spec this as a standard library macro or pragma. Easy peasy. You only need to wipe between syscalls that have side effects. Number crunching AVX heavy subroutines should never have to deal with safety once entered.
- ece 9y agoThis is what KPTI does, wipe caches, and if you did this often in user code, performance degradation would be all over the place. Also, heavy AVX routines that use encryption keys... would be great to attack.
- s4vi0r 9y agoSpectre relies on tricking the CPU into branch predicting its way into accessing protected memory, no? Is it not possible that we can keep most of the performance benefits of speculative execution by somehow having a built in "Hey, never ever speculate that I'll want to access this region of memory" sort of thing?
- senatorobama 9y agoUh, isn't this what AMD does?
- lorenzq 9y agoI read an ars technica article that this would be a possible solution but isn’t right now because the hardware to check access rights isn’t fast enough yet
- ece 9y agoMore likely, this is a shift back to in-order processors, if the solutions aren't workable. If you're in an embedded scenario, sure you can make more trade-offs and have more control, but it's not going to look great when it happens to get hacked.