Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI

[Willy Tarreau]

On Tue, Jan 09, 2018 at 03:51:57PM +0100, Borislav Petkov wrote:
> On Tue, Jan 09, 2018 at 03:36:53PM +0100, Willy Tarreau wrote:
> > I see and am not particularly against this, but what use case do you
> > have in mind precisely ? I doubt it's just saving a few tens of bytes,
> > so probably you're more concerned about the potential risks this opens ?
> > But given we only allow this for CAP_SYS_RAWIO and these ones already
> > have access to /dev/mem and many other things, don't you think there
> > are much easier ways to dump kernel memory in this case than trying to
> > inject some meltdown code into the victim process ? Or maybe you have
> > other cases in mind that I'm not seeing.
> 
> I'd like this to be config-controllable so that distros can make the
> decision whether/if they want to support the whole per-mm thing.

OK.

> Also, if CAP_SYS_RAWIO is going to protect, please make the
> ARCH_GET_NOPTI variant check it too.

Interestingly I removed the check consecutive to the discussions. But
I think I'll simply remove the whole ARCH_GET_NOPTI as it has no real
value beyond initial development.

Willy