On 01/26/2018 04:14 AM, Yves-Alexis Perez wrote: > I know we'll still be able to manually enable PTI with a command line option, > but it's also a hardening feature which has the nice side effect of emulating > SMEP on CPU which don't support it (e.g the Atom boxes above).
For Meltdown-vulnerable systems, it's a no brainer: pti=on. The vulnerability there is just too much. But, if we are going to change the default, IMNHO, we need a clear list of what SMEP emulation mitigates and where. RSB-related Variant 2 stuff on Atom where the kernel speculatively 'ret's back to userspace is certainly a concern. But, there's a lot of other RSB stuffing that's going on that will mitigate that too. Were you thinking of anything concrete? I haven't found anything compelling enough to justify the downsides, especially since things without SMEP tend not to have PCIDs as well.