[baghira]

If you have SMAP, i.e. an Haswell or newer Intel CPU, you should not be vulnerable, so that could be an explanation.

[javanix]

Is SMAP required for mitigation, or is SMEP enough?

IIUC SMEP is on Sandy Bridge processors too.

[benmmurphy]

SMEP would stop this particular exploit because it returns into usermode but SMEP is trivial to bypass on linux if there is no KASLR or other mitigation (apparently there are compiler plugins that remove popular stack pivot gadgets).

[baghira]

According the lwn comments it should be sufficient (and the post by perception-point suggests that it would at least make things more difficult), but I haven't the hardware to test for myself.