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I would assume you have to be root to do this branch predictor stuff. If you're root, why do you need Spectre? If you're attacking some trusted execution thing, then I assume you wouldn't be able to do the branch predictor stuff.

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Because you might be root in one VM or container, and you are trying to access another VM or container.

Oh, interesting. I wonder if the hypervisor would be able to prevent the VM from using those features of the CPU.

it usually does not. reason why you run security analysts of untrusted code first in a qemu without virtualization.

While your hypervisor may not implement it, ARM allows you to configure this kind of operations.

See for example

https://developer.arm.com/documentation/ddi0595/2020-12/AArc...

oh qemu supports this alright, since 8.x

but good luck 1. having a cpu with it (can't wait for arm laptops and needing caniuse.org for my assembly code), and 2. figuring out how to use it

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