Messages in this thread | | | Date | Mon, 8 Jan 2018 18:26:48 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Jan 08, 2018 at 06:05:31PM +0100, Ingo Molnar wrote: > > Note that there is somewhat of a fuzzy detail regarding AMD CPUs which are marked > > as 'Meltdown safe': should an explicit request to turn on PTI be honored by the > > kernel? Should that be some sort of separate 'force PTI on' attribute? > > AMD should not have FEATURE_PTI enabled, and thus not end up in any code > that cares about TIF_NOPTI.
I know, this is the status quo.
Nevertheless:
- if someone disbelieves AMD's claims and wants to force-enable it, should it be possible without patching the kernel?
- or if someone wants to test it on AMD to increase test coverage. pti=on will already be force-enable it on AMD CPUs.
Likewise, there's the counter part on the app level PTI disabling/enabling ABI functionality as well:
- should there be a way for sysadmins to force PTI enabled, even on apps that want to turn it off?
- should there be a way for sysadmins to force PTI disabled, even for apps that want to turn it on?
If we decide that we want to allow fine-grained, per app control of PTI, then all of these look valid scenarios to me.
Thanks,
Ingo
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