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Comment by vetrom | Hacker News Reader

Not always. Cache speculation bugs for example I dont think are covered by emulations. (At least not explicitly. If the mmu model is the same and transparent enough I suppose those could 'pass through' but only if they're implemented on the same plat form.

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You can certainly exploit Meltdown from a VM. The hypervisor tries hard to stay out of the way, and on a properly configured VM the vmexits should be few enough while running compute-bound code that microarchitectural side channels are very well exploitable.

For clarity, in this context I think @ vetrom was talking about emulation, not a virtual machine. A virtual machine makes use of the native instruction set (relying on the hardware) to create a machine within a machine and naturally can only create virtual machines of identical hardware capabilities (or a subset thereof). Emulation does all of that in software and could emulate even a completely different architecture.

Okay, but the original comment said VM and almost every desktop and server has a processor that can natively run x86 in a VM.

Though to get fast emulation, you can re-use techniques from virtual machines (and vice versa).

Btw, emulation is how you can, in principle, run Linux on an 80286. (Normally you'd need a 80386 at least to get memory protection.)

Of course, Linux on the 80286 is gonna be even slower than Linux in your browser. (https://bellard.org/jslinux/)

Using the emulation idea you can go almost arbitrarily primitive. But the 286 is a nice target, because it was a sometimes requested feature in Linux's past.

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