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"..it's not something you can patch easily with a microcode without losing tremendous performance".. Spectre also caused performance drops, could Intel have ma

"..it's not something you can patch easily with a microcode without losing tremendous performance".. Spectre also caused performance drops, could Intel have made these flaws intentionally - just to boost performance?

kevingadd 8y ago
Speculative execution in general is a sizable performance boost that brings in the risk of all sorts of attacks like this. You could of course try to implement it all in a safe way - and of course not every form of speculative execution in existing processors is unsafe - but in practice lots of vendors messed it up and Intel seems to have just produced the least-safe speculative execution implementation. I'd argue that speculative execution's risks were not particularly scary when it became a common technique (a very long time ago!) because things like shared hosting on anonymous machines with hypervisors or multiprocess browser sandboxes storing important data were nearly impossible to predict. AFAIK Intel, ARM and AMD all have shipped chips that are vulnerable to a handful of speculative execution attacks. Microcode can work around these issues by doing things like changing the micro-ops that instructions decode to or disabling processor subsystems - though what they can or can't disable is something I suspect only the vendor knows, it's common for vendors to include many of what are referred to as 'chicken bits' that are essentially panic switches to disable a feature or subsystem if it turns out to be broken.
- tmikaeld 8y ago
  Thanks for a really good explanation, really interesting to know and basically answered my question!
- dfrage 8y ago
  > AFAIK Intel, ARM and AMD all have shipped chips that are vulnerable to a handful of speculative execution attacks. Some ARM CPUs, and IBM, both POWER and mainframe CPUs, have Meltdown bugs. All 4 of these vendors of high performance out-of-order speculative execution CPUs including AMD have Spectre bugs.
- usrusr 8y ago
  > Speculative execution in general is a sizable performance boost that brings in the risk of all sorts of attacks like this. Makes me wonder when we will start seeing physical two-tier architectures, a complete but slower, safety centric system for handling sensitive data on both OS and application level and a souped up "you have been warned about potential leaks" OOE system acting as a general purpose accelerator addon. The difference to existing security enclave concepts would be that the less safe side would be the add-on.
coldtea 8y ago
>Spectre also caused performance drops, could Intel have made these flaws intentionally - just to boost performance? Since no non-Intel CPU expert on Earth looking at those designs didn't think those things were a problem for decades, that's a good reason to assume Intel engineers couldn't either.
- throwaway2048 8y ago
  This overplays things a bit, Intel vulnerabilities like L1TF and Meltdown are directly related to optimization choices they made that people like AMD did not. Not all of these vulnerabilities are equally serious in nature.

kevingadd 8y ago

Speculative execution in general is a sizable performance boost that brings in the risk of all sorts of attacks like this. You could of course try to implement it all in a safe way - and of course not every form of speculative execution in existing processors is unsafe - but in practice lots of vendors messed it up and Intel seems to have just produced the least-safe speculative execution implementation. I'd argue that speculative execution's risks were not particularly scary when it became a common technique (a very long time ago!) because things like shared hosting on anonymous machines with hypervisors or multiprocess browser sandboxes storing important data were nearly impossible to predict. AFAIK Intel, ARM and AMD all have shipped chips that are vulnerable to a handful of speculative execution attacks. Microcode can work around these issues by doing things like changing the micro-ops that instructions decode to or disabling processor subsystems - though what they can or can't disable is something I suspect only the vendor knows, it's common for vendors to include many of what are referred to as 'chicken bits' that are essentially panic switches to disable a feature or subsystem if it turns out to be broken.

tmikaeld 8y ago
Thanks for a really good explanation, really interesting to know and basically answered my question!
dfrage 8y ago
> AFAIK Intel, ARM and AMD all have shipped chips that are vulnerable to a handful of speculative execution attacks. Some ARM CPUs, and IBM, both POWER and mainframe CPUs, have Meltdown bugs. All 4 of these vendors of high performance out-of-order speculative execution CPUs including AMD have Spectre bugs.
usrusr 8y ago
> Speculative execution in general is a sizable performance boost that brings in the risk of all sorts of attacks like this. Makes me wonder when we will start seeing physical two-tier architectures, a complete but slower, safety centric system for handling sensitive data on both OS and application level and a souped up "you have been warned about potential leaks" OOE system acting as a general purpose accelerator addon. The difference to existing security enclave concepts would be that the less safe side would be the add-on.

coldtea 8y ago

>Spectre also caused performance drops, could Intel have made these flaws intentionally - just to boost performance? Since no non-Intel CPU expert on Earth looking at those designs didn't think those things were a problem for decades, that's a good reason to assume Intel engineers couldn't either.

throwaway2048 8y ago
This overplays things a bit, Intel vulnerabilities like L1TF and Meltdown are directly related to optimization choices they made that people like AMD did not. Not all of these vulnerabilities are equally serious in nature.