Running on Intel? If you want security, disable hyper-threading, says Linux kernel maintainer

Speculative execution bugs will be with us for a very long time


Linux kernel dev Greg Kroah-Hartman reckons Intel Simultaneous Multithreading (SMT) - also known as hyper-threading - should be disabled for security due to MDS (Microarchitectural Data Sampling) bugs.

Kroah-Hartman, who was speaking at the Open Source summit in Lyons, has opened up on the subject before. "I gave a talk last year about Spectre and how Linux reacted to it," he told The Reg. "And then this year it's about things found since the last talk. It's more and more of the same types of problems.

"These problems are going to be with us for a long time; they're not going away."

There is another issue, though. "People didn't realise how we do security updates, the whole CVE mess, and the best practices we need to have. Linux isn't less secure or more secure than anything else. The problem is: these are bugs in the chips. We fix them in time, we just have to make sure that everybody updates."

Flushing buffers takes time. Every single one of these mitigations, to solve hardware bugs, slows down your machine ...

Kroah-Hartman explained to attendees how these vulnerabilities "exploit bugs in the hardware when the chip is trying to look into the future".

He added: "MDS is where one program can read another program's data. That's a bad thing when you are running in a shared environment such as cloud computing, even between browser tabs.

"You can cross virtual machine boundaries with a lot of this. MDS exploits the fact that CPUs are hyper-threaded, with multiple cores on the same die that share caches. When you share caches, you can detect what the other CPU core was doing."

OpenBSD was right, he said. "A year ago they said disable hyper-threading, there's going to be lots of problems here. They chose security over performance at an earlier stage than anyone else. Disable hyper-threading. That's the only way you can solve some of these issues. We are slowing down your workloads. Sorry."

Kroah-Hartman, a kernel maintainer, described some post-Spectre MDS examples, like RIDL, Fallout and Zombieland. "You can steal data across applications. You can steal data across virtual machines. And across 'secure enclaves', which is really funny. Inside Intel chips there is something called SGX [Software Guard Extensions] where you can run code that nobody else can see, it's really porous. In the kernel we fix this by flushing buffers every time we switch context. It solves the problem."

But then there's the performance hit. "Flushing buffers takes time. Every single one of these mitigations, to solve hardware bugs, slows down your machine."

The extent of the slowdown depends on the workload. If it is IO-bound, you may hardly notice. But Kroah-Hartman builds kernels. "I see a slowdown of about 20 per cent. That's real. As kernel developers we fight for a 1 per cent, 2 per cent speed increase. Put these security things in, and we go back like a year in performance. It's sad."

Kroah-Hartman dispelled the idea that an issue like Spectre has a single fix. "We are still fixing Spectre 1.0 issues [almost] two years later. It's taken a couple of thousand patches over [almost] two years. Always take the latest kernel and always take the latest BIOS update."

The CVE database of security issues is irrelevant when it comes to the Linux kernel, he said. "CVEs mean nothing, for the kernel. Very few CVEs ever get assigned for the kernel. I'm fixing 20 patches a day, I could create a CVE to each one of them, I was told not to because it would burn the world down," he said.

"If you're not using a supported distro, or a stable long-term kernel, you have an insecure system. It's that simple. All those embedded devices out there, that are not updated, totally easy to break. If you are running in a secure environment and you trust your applications and you trust your users then get the speed back. Otherwise, running in a shared environment, running untrusted code, you need to be secure."

Is AMD safer than Intel? "All the issues that came out this year, were reported not to be an issue on AMD," he told us. Would he enable SMT on AMD? "As of today, that is still a safe option from everything I know. Yes."

Are the MDS vulnerabilities being actively exploited by malware? "They're not that hard to exploit," Kroah-Hartman said. "The research has proved how to do it. The hard part is, you can't tell if somebody is exploiting it. But it is a known problem, you can reproduce it yourself. The Zombieland guys have a great demo. It's a real issue, you need to fix it."

SUSE queue?

As it happens, next up for The Register at the Open Source Summit was SUSE EMEA CTO Gerald Pfeifer. Naturally, we asked him whether SUSE ships with hyper-threading on or off by default.

"On," he said. "Greg K-H? He's right. Ultimately every customer needs to decide, because there is a cost associated with it. But from a technical perspective he's right."

Imagine, he said, you were Google. "Making that switch means one, two, three more data centres. I'm not arguing leave it on. All I'm saying is, it's not an easy choice. Because someone is going to yell at you if something takes longer."

So there you have it. If you're running on Intel, but want to be secure: best practice is to disable hyper-threading and keep your BIOS and kernel up to date. In reality, though, many factors conspire against that best practice being achieved. ®

Similar topics


Other stories you might like

  • Lonestar plans to put datacenters in the Moon's lava tubes
    How? Founder tells The Register 'Robots… lots of robots'

    Imagine a future where racks of computer servers hum quietly in darkness below the surface of the Moon.

    Here is where some of the most important data is stored, to be left untouched for as long as can be. The idea sounds like something from science-fiction, but one startup that recently emerged from stealth is trying to turn it into a reality. Lonestar Data Holdings has a unique mission unlike any other cloud provider: to build datacenters on the Moon backing up the world's data.

    "It's inconceivable to me that we are keeping our most precious assets, our knowledge and our data, on Earth, where we're setting off bombs and burning things," Christopher Stott, founder and CEO of Lonestar, told The Register. "We need to put our assets in place off our planet, where we can keep it safe."

    Continue reading
  • Conti: Russian-backed rulers of Costa Rican hacktocracy?
    Also, Chinese IT admin jailed for deleting database, and the NSA promises no more backdoors

    In brief The notorious Russian-aligned Conti ransomware gang has upped the ante in its attack against Costa Rica, threatening to overthrow the government if it doesn't pay a $20 million ransom. 

    Costa Rican president Rodrigo Chaves said that the country is effectively at war with the gang, who in April infiltrated the government's computer systems, gaining a foothold in 27 agencies at various government levels. The US State Department has offered a $15 million reward leading to the capture of Conti's leaders, who it said have made more than $150 million from 1,000+ victims.

    Conti claimed this week that it has insiders in the Costa Rican government, the AP reported, warning that "We are determined to overthrow the government by means of a cyber attack, we have already shown you all the strength and power, you have introduced an emergency." 

    Continue reading
  • China-linked Twisted Panda caught spying on Russian defense R&D
    Because Beijing isn't above covert ops to accomplish its five-year goals

    Chinese cyberspies targeted two Russian defense institutes and possibly another research facility in Belarus, according to Check Point Research.

    The new campaign, dubbed Twisted Panda, is part of a larger, state-sponsored espionage operation that has been ongoing for several months, if not nearly a year, according to the security shop.

    In a technical analysis, the researchers detail the various malicious stages and payloads of the campaign that used sanctions-related phishing emails to attack Russian entities, which are part of the state-owned defense conglomerate Rostec Corporation.

    Continue reading
  • FTC signals crackdown on ed-tech harvesting kid's data
    Trade watchdog, and President, reminds that COPPA can ban ya

    The US Federal Trade Commission on Thursday said it intends to take action against educational technology companies that unlawfully collect data from children using online educational services.

    In a policy statement, the agency said, "Children should not have to needlessly hand over their data and forfeit their privacy in order to do their schoolwork or participate in remote learning, especially given the wide and increasing adoption of ed tech tools."

    The agency says it will scrutinize educational service providers to ensure that they are meeting their legal obligations under COPPA, the Children's Online Privacy Protection Act.

    Continue reading
  • Mysterious firm seeks to buy majority stake in Arm China
    Chinese joint venture's ousted CEO tries to hang on - who will get control?

    The saga surrounding Arm's joint venture in China just took another intriguing turn: a mysterious firm named Lotcap Group claims it has signed a letter of intent to buy a 51 percent stake in Arm China from existing investors in the country.

    In a Chinese-language press release posted Wednesday, Lotcap said it has formed a subsidiary, Lotcap Fund, to buy a majority stake in the joint venture. However, reporting by one newspaper suggested that the investment firm still needs the approval of one significant investor to gain 51 percent control of Arm China.

    The development comes a couple of weeks after Arm China said that its former CEO, Allen Wu, was refusing once again to step down from his position, despite the company's board voting in late April to replace Wu with two co-chief executives. SoftBank Group, which owns 49 percent of the Chinese venture, has been trying to unentangle Arm China from Wu as the Japanese tech investment giant plans for an initial public offering of the British parent company.

    Continue reading
  • SmartNICs power the cloud, are enterprise datacenters next?
    High pricing, lack of software make smartNICs a tough sell, despite offload potential

    SmartNICs have the potential to accelerate enterprise workloads, but don't expect to see them bring hyperscale-class efficiency to most datacenters anytime soon, ZK Research's Zeus Kerravala told The Register.

    SmartNICs are widely deployed in cloud and hyperscale datacenters as a means to offload input/output (I/O) intensive network, security, and storage operations from the CPU, freeing it up to run revenue generating tenant workloads. Some more advanced chips even offload the hypervisor to further separate the infrastructure management layer from the rest of the server.

    Despite relative success in the cloud and a flurry of innovation from the still-limited vendor SmartNIC ecosystem, including Mellanox (Nvidia), Intel, Marvell, and Xilinx (AMD), Kerravala argues that the use cases for enterprise datacenters are unlikely to resemble those of the major hyperscalers, at least in the near term.

    Continue reading

Biting the hand that feeds IT © 1998–2022