Intel’s Spectre ‘Variant 4’ Efficiency Examined: Speculative Retailer Bypass

Today we're taking a look at the effects of the Specter Variant 4 CPU error on Intel's 8th generation Core CPUs (Coffee Lake). When the Meltdown and Specter vulnerabilities were released in early 2018, we knew this would be an ongoing process.

The first patches didn't take care of everything. They dealt with variant 1, better known as meltdown, and then with two Specter errors known as variant 2 and 3. Although Intel and Microsoft recently released variant 4 updates, a related attack called "Speculative Store Bypass" was carried out.

The speculative store bypass affects not only Intel, but also AMD and ARM. However, AMD and ARM processors can be repaired with a simple software update. So if you keep your operating system and web browser up to date, you will automatically be protected from variant 4.

If you have an Intel processor, not only software but firmware updates are required to fully resolve the issue, ie a BIOS update. A few months ago, Intel started delivering variant 4 microcode patches to its hardware partners in beta form. Only now do we see how manufacturers bring them out. As far as I know, Asus is the only board manufacturer that has done this so far.

The latest round of BIOS updates from Asus contains the updated microcode for variant 4, but is not activated by default in Windows. At the moment it has to be activated manually by adding some registry keys. It is likely that this will happen automatically at some point.

I suspect Microsoft is concerned about a repeat of the disaster that occurred in fixing the first wave of vulnerabilities. This time, they have been more careful.

According to Intel, activating the fix results in a performance drop of around 2 to 8%. This was observed during benchmarking with SYSmark 2014 on client and server test systems. I'm sure many of you want to know how this affects your system's performance. There should be no impact for AMD users, and we'll examine that soon.

Right now we're going to see what impact this has on those using a Coffee Lake CPU (8th generation core), which is so far the only platform to get the BIOS update. For testing we use the Core i7-8700 on the Asus ROG Strix Z370-F gaming motherboard using BIOS version 1002. I will compare the results with SSB enabled and disabled. Activated is marked as a "pre-update" and deactivated as & # 39; Specter v4 Update & # 39 ;. So let's get to the results.

Benchmarks

First we have the Cinebench R15 results and here we see no change at all if the patch for variant 4 is activated. The single thread score remains unchanged and the same applies to the multi-core score. 3fps are well within the range of errors here.

The CPUz benchmark recorded a decline of 3% in the single-thread test and only 1% in the multithread test. These results were always repeatable.

The Corona benchmark was run half a dozen times for each configuration, and we found that Variant 4 attenuations only affected performance by 1%, not much, but we consistently saw a 1% performance drop.

Here we see no change in performance when testing with 7-zip, less a 1% difference between the two test configurations.

If we move on to some games and find only very few chances when benchmarking with Battlefield 1, the 1% low result was consistently lower when the update for variant 4 was activated. So we're talking about a 2% drop in performance.

In Far Cry 5, the average frame rate only dropped by 1.5%, the minimum by 1%, and although the update for variant 4 consistently slowed the Core i7-8700 by 1 – 2 fps, this is not exactly a great performance .

When testing with Rainbow Six Siege, we only see a hit of 1 – 2 fps.

Finally, we looked at Fortnite and here we see a slightly larger 3% drop in average performance and frame time performance. Again not a big change, but we constantly saw a drop in performance of 4-5 fps.

closing remarks

Intel anticipated a 2–8% drop in performance if the Variant 4 vulnerability was addressed by disabling the Speculative Store Bypass. In our tests, however, it looks more like 1 to 3%. The impact for Linux users seems to be more in line with Intel's claim, and we believe this is due to the Windows scheduler, which is less efficient than that of Linux.

When patching variants 1, 2 and 3, we noticed a game performance reduction of up to 5% on the i7-8700K, although the frame rates mostly decreased by 0 to 3%. Variant 4 saw a further decrease of 1 to 3%, although we tested this time with the non-K 8700, but the edges should be largely the same over the entire range.

In other words, since December, the gaming performance of Intel Coffee Lake CPUs has decreased by 1 to 6%, or about 1-2 fps in games with more than 60 fps and up to 5 fps for games with high refresh rates. Overall, definitely not a big deal, but it's worth considering that Intel will suffer an IPC hit due to future architectures that address these hardware-level vulnerabilities.

Those of you who are lucky enough to have an 8th generation Intel Core processor don't have to worry about your games turning into a slideshow, as the impact on performance isn't significant. But even if this were the case, we would have strongly recommended that you update your BIOS and activate the damage limitation as soon as possible.

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