Scratches PowerPC off the list of trustworthy CPUs
Sooo, out you go, G5. Any suggestions what to use for online banking? A 486 can't handle all the jQuery and tracking scripts.
Sooo, out you go, G5. Any suggestions what to use for online banking? A 486 can't handle all the jQuery and tracking scripts.
In this specific instance, the xdcbt instruction accidentally does a bad thing in the Spectre Zone that leaks back into the real world through a side-channel in the L1 cache. Crafted malicious code could do another bad thing in the Spectre Zone that ordinarily isn't allowed in the real world, then leak the results back to the real world through any side-channel that works.
Only on Xbox 360, it could even use xdcbt vs dcbt for that side-channel. If you set code up to always execute xdcbt on core 2, and always dcbt on cores 0 and 1, you might be able to do timing-based attacks between core 0 (closer to L2) and core 1 (further from L2) comparing against core 2 (bypassing L2).
A different version of the same PowerPC chip family would have its own side-channels. All those side-channels are hardware-specific.
The 360 cpu (and the closely related ps3 cpu) is the perfect example of this. Despite the fact that it's 100% in-order, it has a very long instruction pipeline (upto 50 instructions long) and branch prediction. And that's all Spectre needs, a long pipeline + branch prediction.
I'm not even 100% sure the intel atom will be safe from Spectre & Meltdown. It's pipeline is much shorter, only 16 stages long, but it still speculatively executes up-to 32 instructions (2 instructions per cycle).
It just makes things harder, you have to find a Spectre gadget that's short enough. Though piss-easy for Meltdown, because you can just hand-assemble short code.