Windows 10 Update Brings Google’s Retpoline Spectre Mitigation

• The latest Windows 10 update comes with the Retpoline Spectre mitigation and several fixes.
• It took a while for Retpoline to land on Windows, but kernel engineers promise its effect on your system’s performance will be negligible.
• The Spectre vulnerability still remains a problem, but updating will mitigate the risks by far.

Microsoft has started rolling out a cumulative update for Windows 10 version 1809, with the name-code “KB4482887”. This update enables the “Retpoline” mitigation that addresses the Spectre variant 2 (CVE-2017-5715) vulnerability. Retpoline was developed by Google’s Project Zero team, to increase protection against “branch target injection” attacks, and has already found its way in major Linux distributions throughout 2018. Microsoft was a bit late to incorporate Retpoline into the Windows kernel, with the development manager Mehmet Iyigun, claiming that the delays were due to the involved technical complexities. Retpoline has finally arrived, so it’s time for everyone to update immediately.

Besides mitigating the Spectre risks, Retpoline is also explicitly developed and implemented by Microsoft’s engineers to not to impact the kernel performance by much. Google had presented some performance affection figures last year, claiming an impact of 1.5% on Google Cloud servers. However, these numbers were significantly higher on Linux distributions that incorporated the Retpoline mitigation. Still though, having a slower and more secure system is preferable against having a speedy but vulnerable one.

The drop in performance stems from the fact that Retpoline restrains the prediction actions of the processor, which is precisely what can be abused in the context of the Spectre vulnerability. This means that no calculation branch predictions can occur, and so the operation is less optimized than the default. Google tried to somewhat lessen the adverse effects of this restrictive approach by providing the capacity to add direct branch hints manually, offering kernel developers the option for a “guided optimization”.

Other notable improvements and fixes that come bundled in the particular update include Edge PDF fixes, Action Center display bug fixes, disk detection error fixes, laptop “Sleep” mode optimizations, Windows Server 2019 Remote Desktop performance issue improvements, Bluetooth radio peripherals support, MP4 parsing and playback improvements, Internet Explorer experience improvements, and S2D problem fixes.

Some may experience Internet Explorer 11 authentication problems after updating, while others may receive an “Error 1309” when running MSI and MSP files. For the first problem, people are advised to create unique user accounts when logging on to a Windows Server system and disable multiple RDP sessions. For the 1309 error, users are simply to ignore it as a fix is on the way.

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