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Researchers discover yet another spectre-related vulnerability attacking Intel's and AMD's Micro-Op Caches.

orcv
By orcv
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Researchers detail three new Intel and AMD Spectre vulnerabilities | Engadget

 

For CPU makers, one of the biggest concerns will be the performance impacting mitigation measures outlined by the researchers, including the flushing of the micro-op cache at domain crossings or privilege level-based partitioning of the caches. The paper's authors claim this mitigation would come with "much greater performance penalty" than those related to previous attacks.

 

The first of the trio of possible exploits is a same thread cross-domain attack that leaks secrets across the user kernel boundary. A separate variant relies on a cross-SMT thread attack that transmits secrets across two SMT threads via the micro-op cache. The paper also describes "transient execution attacks" that can be used "to leak an unauthorized secret accessed along a misspeculated path, even before the transient instruction is dispatched to execution."

 

If true, disabling HT would actually be less performance impactful than the mitigation of leaving it on.

 

Now if disabling HT doesn't mitigate, well, we're all in a world of hurt.

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On 5/1/2021 at 10:12 AM, Arika S said:

Humans have created technology so complex that no one can possibly understand how they work to a degree where there will never be vulnerabilities. 

It's not really an issue that's dependent on complexity or lack of understanding it's the simple fact we are humans so everything we do will be inherently "flawed" in some way. I do agree though software is getting very complex and we are loosing the old knowledge of the engineers who grew up on punch cards. So most code is just stack overflow copy and paste 

▓ƆԀ▓ S▓₱▓Ɇ▓c▓s▓: i7 6ʇɥפᴉƎ00K (4.4ghz), Asus DeLuxe X99A II, GT҉X҉1҉0҉8҉0 Zotac Amp ExTrꍟꎭe),Si6F4Gb D???????r PlatinUm, EVGA G2 Sǝʌǝᘉ5ᙣᙍᖇᓎᙎᗅᖶt, Phanteks Enthoo Primo, 3TB WD Black, 500gb 850 Evo, H100iGeeTeeX, Windows 10, K70 R̸̢̡̭͍͕̱̭̟̩̀̀̃́̃͒̈́̈́͑̑́̆͘͜ͅG̶̦̬͊́B̸͈̝̖͗̈́, G502, HyperX Cloud 2s, Asus MX34. פN∩SW∀S 960 EVO

Just keeping this here as a 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Does this affect older chips (such as Phenom II's, 2nd gen) or just recent ones (such as Zen 2, Intel 9th gen, etc.)

elephants

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On 5/1/2021 at 9:14 AM, StDragon said:

So far, the only sure way to mitigate all forms of Spectre is to disable hyperthreading. If the same mitigation holds true for this form, I think it's the final nail in the coffin for this feature.

 

If the above statement is true, then I expect a plateau in thread count for a generation or two as HT is disabled while physical core count increases. But on the bright side, it's not so bad of a move because we now have chips with more physical cores than most could really need anyways. So there is a silver lining in all this.

 

It's more likely the push to big-little designs will result in "little cores" replacing hyperthread/smt features. Little cores might lose features from performance cores that consume power or space but aren't used by all programs.

 

This is what ARM does:

Cortex-A50-series.png

 

So if you remember how hyperthread actually was originally designed, it splits a single Pentium 4 into two logical cores by splitting the pipeline in two but still sharing the decoder phase.

 

(This is from 2008)

http://users.encs.concordia.ca/~hotpoint/comp326/hyperthreading.pdf

Which cites a document from 2002

ftp://download.intel.com/technology/itj/2002/volume06issue01/art01_hyper/vol6iss1_art01.pdf

 

image.thumb.png.ae2e4a6cc907108ef23c33eec9800f2f.png

 

image.thumb.png.9b8cfeb321451f0d012c8ec1498771e0.png

 

So if exploits keep being found that are a consequence of HT features, we may just be better off dispensing with the feature, cut the pipeline in half to make the core smaller and just have more cores, which is what I suspect "little" cores really are in these big.little implementations.

 

However I also suspect that the various L1/L2/L3 caches might also have to be carved into individual core's and negate the performance benefit of sharing it between cores/hyperthreads to just prevent the security issues from existing in the first place, as I imagine adding all the security features to make "it safer" is an arms race and bloats the cpu design as well. 

 

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56 minutes ago, Kisai said:

It's more likely the push to big-little designs will result in "little cores" replacing hyperthread/smt features. Little cores might lose features from performance cores that consume power or space but aren't used by all programs.

...

So if you remember how hyperthread actually was originally designed, it splits a single Pentium 4 into two logical cores by splitting the pipeline in two but still sharing the decoder phase.

 

(This is from 2008)

http://users.encs.concordia.ca/~hotpoint/comp326/hyperthreading.pdf

Which cites a document from 2002

ftp://download.intel.com/technology/itj/2002/volume06issue01/art01_hyper/vol6iss1_art01.pdf

...

So if exploits keep being found that are a consequence of HT features, we may just be better off dispensing with the feature, cut the pipeline in half to make the core smaller and just have more cores, which is what I suspect "little" cores really are in these big.little implementations.

SMT is made to make better use of the idling execution units inside a CPU. Halving the pipeline won't make much difference in the die area, you'll still have all of the EUs inside of it, and now those won't be used by most applications.

You're mistaking things. A little core is an actual core that you can throw tasks for it to do. SMT, in layman terms, is just another pipeline in order to make the CPU be able to schedule more EUs at once instead of having those sitting idle because most applications can't make proper use of ILP. In the end, you're comparing apples to oranges.

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2 hours ago, Kisai said:

 

It's more likely the push to big-little designs will result in "little cores" replacing hyperthread/smt features. Little cores might lose features from performance cores that consume power or space but aren't used by all programs.

 

This is what ARM does:

Cortex-A50-series.png

 

So if you remember how hyperthread actually was originally designed, it splits a single Pentium 4 into two logical cores by splitting the pipeline in two but still sharing the decoder phase.

 

(This is from 2008)

http://users.encs.concordia.ca/~hotpoint/comp326/hyperthreading.pdf

Which cites a document from 2002

ftp://download.intel.com/technology/itj/2002/volume06issue01/art01_hyper/vol6iss1_art01.pdf

 

image.thumb.png.ae2e4a6cc907108ef23c33eec9800f2f.png

 

image.thumb.png.9b8cfeb321451f0d012c8ec1498771e0.png

 

So if exploits keep being found that are a consequence of HT features, we may just be better off dispensing with the feature, cut the pipeline in half to make the core smaller and just have more cores, which is what I suspect "little" cores really are in these big.little implementations.

 

However I also suspect that the various L1/L2/L3 caches might also have to be carved into individual core's and negate the performance benefit of sharing it between cores/hyperthreads to just prevent the security issues from existing in the first place, as I imagine adding all the security features to make "it safer" is an arms race and bloats the cpu design as well. 

 

According to the (not super well designed) diagram above, Hyperthreading and SMT is not duplicating of pipeline components, rather, allowing a means to utilize resources that an individual thread has left untouched. 
 

Duplicating of pipeline resources is referred to as Superscalar, or widening of the pipeline. SMT isn’t the only means that a wider pipeline can be put to use, as reordering of instructions can allow even single threads to be broken up into parallel instructions. 
 

Losing SMT means more aggressive OoO execution to properly utilize resources and maintain efficiency, at potential security implications of its own, or the onus is put on the programmers to code their app to utilize the architecture, which is highly specific, and expensive from a time perspective. 

Going narrower on the architecture (making them smaller) will mean necessitating higher clock speeds to make up the performance deficit, as some performance-sensitive applications will miss the cut resources. The problems incurred with ramping up clocks should be readily apparent. Though if a future Silicon replacement can reach dozens or hundreds of GHz (or even THz), smaller, simpler cores can be phased in, eliminating speculative security flaws entirely. Much faster RAM (both latency and bandwidth) would also help, as much of the reason CPUs perform speculation in the first place is to overcome memory being comparatively very slow. 

 

Going to cache, in a modern SoC and many PC CPUs, splitting up the caches (especially last level) is not a tenable solution, as other SoC components (such as the GPU) also require fast caches, but due to power consumption and die size constraints, giving everything enough cache to fully utilize resources will likely require pretty steep compromises. 

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My camera lens sees the present…

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