Friday, August 11th 2023
"Downfall" Intel CPU Vulnerability Can Impact Performance By 50%
Intel has recently revealed a security vulnerability named Downfall (CVE-2022-40982) that impacts multiple generations of Intel processors. The vulnerability is linked to Intel's memory optimization feature, exploiting the Gather instruction, a function that accelerates data fetching from scattered memory locations. It inadvertently exposes internal hardware registers, allowing malicious software access to data held by other programs. The flaw affects Intel mainstream and server processors ranging from the Skylake to Rocket Lake microarchitecture. The entire list of affected CPUs is here. Intel has responded by releasing updated software-level microcode to fix the flaw. However, there's concern over the performance impact of the fix, potentially affecting AVX2 and AVX-512 workloads involving the Gather instruction by up to 50%.
Phoronix tested the Downfall mitigations and reported varying performance decreases on different processors. For instance, two Xeon Platinum 8380 processors were around 6% slower in certain tests, while the Core i7-1165G7 faced performance degradation ranging from 11% to 39% in specific benchmarks. While these reductions were less than Intel's forecasted 50% overhead, they remain significant, especially in High-Performance Computing (HPC) workloads. The ramifications of Downfall are not restricted to specialized tasks like AI or HPC but may extend to more common applications such as video encoding. Though the microcode update is not mandatory and Intel provides an opt-out mechanism, users are left with a challenging decision between security and performance. Executing a Downfall attack might seem complex, but the final choice between implementing the mitigation or retaining performance will likely vary depending on individual needs and risk assessments.
Source:
Phoronix
Phoronix tested the Downfall mitigations and reported varying performance decreases on different processors. For instance, two Xeon Platinum 8380 processors were around 6% slower in certain tests, while the Core i7-1165G7 faced performance degradation ranging from 11% to 39% in specific benchmarks. While these reductions were less than Intel's forecasted 50% overhead, they remain significant, especially in High-Performance Computing (HPC) workloads. The ramifications of Downfall are not restricted to specialized tasks like AI or HPC but may extend to more common applications such as video encoding. Though the microcode update is not mandatory and Intel provides an opt-out mechanism, users are left with a challenging decision between security and performance. Executing a Downfall attack might seem complex, but the final choice between implementing the mitigation or retaining performance will likely vary depending on individual needs and risk assessments.
162 Comments on "Downfall" Intel CPU Vulnerability Can Impact Performance By 50%
Common hardware (as desktops are more or less cut down enterprise hardware these days) means we're vulnerable tooTheres been some pretty big updates along the way, but also several small ones that had little change
Every major release had major changes - entire ranges of CPUs added in, new features like ReBar, default settings changes for windows 11, and so on.
Beta and test releases can count or not count depending on your perspective - they're both major in that they had the big improvements first, but minor in that they weren't the final release of that feature.
Then board makers could put out 20 BIOS updates on the same AGESA code fixing their own shit which is a different metric again
I do agree that not every update was critical by the way, just saying that depending how you view it it can seem that way - check Asus BIOS lists for the boards and the only remaining visible files are those major updates with the minor ones removed from view
I mean, we're all vulnerable against bullets, but who's gonna shoot me doing my normal things in the English Midlands? Buying a bulletproof vest to do my weekly shopping wouldn't be too practical.
If the microcode update comes through Windows Update, then sure, whatever. I just don't want to worry about something that has near zero chance to affect me.That's why one should read the release notes and decide whether upgrading is necessary or not. There's been quite a few BIOS updates for my board (Pro B650M-A Wifi) with the same AGESA code as the last one and only "memory compatibility improved" in the release notes. If my system is already running fine, I don't bother with such updates at all.
Therefore, no ones going to hack home users and leave it running 24/7 and manually sniff the data to find out if anything useful was found
These hacks are only useful against something that's crunching high value data every day, so that eventually with even a low chance of success you get something useful.
Country vs country espionage, not steal a netbanking login cookie with one chance of success for one random second of one day a month, with no guarantees the user will be using the netbanking in that second, or that it'll be ran off an SMT thread where the vulnerability occured
My 9900KS misted the last Vulnerability attacks. That pledged most SkyLake lines. Intel added hardware the fix to 9900KS line.
Glad this Vulnerable attack doesn't effect any of the LGA 1700 socket lineups 12th, 13th, 14th Generations.
Cheers
Note downfall isnt listed on this link and is also some older one's not listed here, there is probably a newer article for downfall.
support.microsoft.com/en-au/topic/kb4072698-windows-server-and-azure-stack-hci-guidance-to-protect-against-silicon-based-microarchitectural-and-speculative-execution-side-channel-vulnerabilities-2f965763-00e2-8f98-b632-0d96f30c8c8e
usa.kaspersky.com/resource-center/definitions/heuristic-analysis
www.kaspersky.com/enterprise-security/wiki-section/products/exploit-prevention
support.kaspersky.com/KSVLA/5.0/en-US/74649.htm
Interestingly Linux mitigations do not require new microcode on Zen 3 and 4, but have slightly decreased performance penalty with it present (available currently only on server EPYC line).
There are two gaming-related benchmarks on desktop Zen 4 (3DMark Wild Life Extreme and VKMark) showing minimal impact, so one can reasonably assume that pure gaming won't be affected either. However to be sure it has to be tested. Windows mitigations might also have different result.
Most affected workloads are heavy I/O users like databases and web servers, so it looks like context switching is penalized.
The registry keys are, as far as I understand, also mutually exclusive since they toggle different bits in the FeatureSettingsOverride value.
Their PowerShell module doesn't support AMD vulnerabilities either.
I hope that I'm interpreting this wrong, otherwise it's quite disappointing.