Windows/Azure kernel team member Mehmet Iyigun has confirmed that the next significant Windows 10 update (19H1) will include Google’s Retpoline, a software-based mitigation for Spectre that affects performance only marginally compared to Microsoft’s earlier patches. 19H1 is expected to release early next year.



Retpoline as a mitigation strategy swaps indirect branches for returns, to avoid using predictions which come from the BTB, as they can be poisoned by an attacker. The problem with Skylake+ is that an RSB underflow falls back to using a BTB prediction, which allows the attacker to take control of speculation.

Discussion

Source: [H]ardOCP – Windows 10 19H1 Update to Reduce Performance Impact of Spectre Mitigation