Re: Intel CPU design flaw - FreeBSD affected?

On Thu, Jan 4, 2018 at 7:33 AM, Stefan Esser <se_at_freebsd.org> wrote:

> Am 04.01.18 um 12:56 schrieb Darren Reed:
> > On 4/01/2018 11:51 AM, Mark Heily wrote:
> >> On Jan 2, 2018 19:05, "Warner Losh" <imp_at_bsdimp.com> wrote:
> >>
> >> The register article says the specifics are under embargo still. That
> would
> >> make it hard for anybody working with Intel to comment publicly on the
> flaw
> >> and any mitigations that may be underway. It would be unwise to assume
> that
> >> all the details are out until the embargo lifts.
> >>
> >>
> >> Details of the flaws are now published at:
> >>
> >> https://meltdownattack.com
> >
> > The web page has both: meltdown and spectre.
> > Most people are only talking about meltdown which doesn't hit AMD.
> > spectre impacts *both* Intel and AMD.
> >
> > SuSE are making available a microcode patch for AMD 17h processors that
> > disables branch prediction:
> >
> > https://lists.opensuse.org/opensuse-security-announce/
> 2018-01/msg00004.html
>
> Disabling branch prediction will have a very noticeable effect on execution
> speed in general (while split page tables only affect programs that perform
> system calls at a high frequency).
>
> I have not fully read the Meltdown and Spectre papers, yet, but I do
> assume,
> that the attack at the branch prediction tries to counter KASLR, which we
> do
> not support at all in FreeBSD.
>
> So, I guess, we do not have to bother with disabling of branch prediction
> in
> FreeBSD for the time being?
>

Branch prediction has nothing to do with defeating KASLR. It's rather the
whole crux of the attack. Disabling it is one way to prevent Specter.

The only thing that will help Meltdown, though, is separate page tables.

It's only an incidental foot note that these methods don't care about KASLR
and KASLR isn't at all effective in blunting these attacks.

Warner