Meltdown, Spectre, and what they mean for Linux users

Performance

The measures for containing Meltdown and Spectre reduce the computing power of all affected processors, with the measures that target Meltdown leading to the biggest declines. Performance losses for desktop computers usually do not exceed five percent, but servers can lose 30 percent or more, depending on the usage profile.

The effects depend strongly on the number of system calls and the context change between user space and kernel due to page table isolation. Both Intel and the kernel developers expect to reduce the performance impact in the near future.

Conclusions

Linux users are the most up to date when it comes to Meltdown and Spectre: Either Linux 4.16.x or the back-patched LTS kernels of the 4.4, 4.9, and 4.14 series are the benchmark. Users should ditch any distribution that is not kept up to date. In contrast, Windows users are in the dark, as all protections are delivered to them with a time delay. BSD was given its first patches on February 17; the BSD patches resemble those for Linux.

The fundamental problem lies in the silicon of the processors and can only be solved there. Even a new stepping level revision of a CPU takes up to three years and costs millions. (A stepping is a sub-version of a processor generation, corresponding to a minor version change for software – also known as a core revision at AMD.) It is also questionable whether all necessary countermeasures could be accommodated in a single stepping. Another difficulty is fixing the vulnerabilities without creating new bugs.

Cautious estimates assume that the Meltdown and Spectre gaps could still be lurking in the background for a decade. The new MeltdownPrime and SpectrePrime variations announced in February require further changes to the silicon – and they are unlikely to be the last.

So far, it is unlikely that any malware in the wild can actually exploit Meltdown and Spectre. But any delays in implementation are a reflection on the complexity of the attack vectors – not the interest of the attackers. The first, fortunately still ineffective, malware that exploits the gaps is already appearing.

The most complete information on Meltdown and Spectre was published by the discoverers of the vulnerabilities in Google's Project Zero [10]. You can check the current state of protection for your own hardware with a script that you download from GitHub [11] and run as root (Listing 1). Under the latest Debian and Ubuntu versions, install the script directly from the repositories using the spectre-meltdown-checker package.

Listing 1

Vulnerability Check

$ wget meltdown.ovh -O spectre-meltdown-check
$ chmod u+x spectre-meltdown-checker.sh
$ sudo ./spectre-meltdown-checker.sh

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