Messages in this thread | | | Subject | Re: [PATCH v3 5/6] x86/pti: Do not enable PTI on processors which are not vulnerable to Meltdown | From | Arjan van de Ven <> | Date | Fri, 26 Jan 2018 07:30:15 -0800 |
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On 1/26/2018 7:27 AM, Dave Hansen wrote: > 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?
not Atom though. Atom has has SMEP for a very long time, at least the ones that do speculation do afaict.
SMEP is for other bugs (dud kernel function pointer) and for that, emulating SMEP is an interesting opt-in for sure.
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