It can’t be. The problem is C. One must prevent speculation altogether unless one has information on bounds used in speculated branches. mem[__builtin_speculation_safe_value (untrusted)]; Now if the cpu had data about the data dependencies protected (sic) by branches on bounds
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The problem is not C, it's speculation. Explicitly marking up sensitive data rather than having the cpu do its job and enforce its contractual protections does not scale and is a losing battle before you even start.
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I think there's a really good chance someone who studied the way the microcode works deeply enough would find a way to disable speculation, make all instructions speculation barriers, kill all branch prediction, or do something else that would completely defang Spectre.
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There are all these other side channels popping up like L1TF. Avoiding access check delay for use of L1 cache data in speculated loads. It’s all the little performance tricks to meet timing. i.e. why your chip can turbo boost to 4GHz
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Perfectly cool with it deturboing to 500 MHz.
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IIRC it's signed, so maybe reverse engineering microcode patches, and finding vulnerability in the signature mechanism of the patches ;-)
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I like the idea of speculation buffering such that speculative loads don’t cause evictions until their branches have been resolved. i.e. eviction has a dependency on the condition that the load has been taken. Commit txid from speculation buffer in cache. Defer evictions.
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Unless it does blinding. i.e. does random cache evictions using entropy from a metastable circuit, vs using a CSPRNG. Still that can be influenced using RF by a physically collocated attacker vs a virtually collocated attacker. An improvement.
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