[Libre-soc-isa] [Bug 585] add bounds-checked load/store instructions for WebAssembly

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=585

--- Comment #3 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #1)
> i wonder if fine-grained IOMMU would do the job well.

I don't think that's the right place to do the bounds checking, since it needs
to happen before the MMU's page table lookup (IOMMU happens after MMU
translation iirc) otherwise we have to allocate 4GB of memory space again (or
have a separate bounds check beforehand for 64-bit wasm addresses) defeating
the whole purpose of the additional support.

remember, wasm is designed to run potential-attacker code in-process with
runtime bounds checks to prevent wasm from accessing memory outside of the
assigned range.

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