Re: [PATCH v4 01/12] Documentation: Document arm64 kpti control

[Jeremy Linton]

Hi,


I just realized I replied to this off-list.

On 01/30/2019 12:02 PM, Andre Przywara wrote:
> On Fri, 25 Jan 2019 12:07:00 -0600
> Jeremy Linton <jeremy.linton@xxxxxxx> wrote:
>
> Hi,
>
> > For a while Arm64 has been capable of force enabling
> > or disabling the kpti mitigations. Lets make sure the
> > documentation reflects that.
> >
> > Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> > Cc: Jonathan Corbet <corbet@xxxxxxx>
> > Cc: linux-doc@xxxxxxxxxxxxxxx
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > b/Documentation/admin-guide/kernel-parameters.txt index
> > b799bcf67d7b..9475f02c79da 100644 ---
> > a/Documentation/admin-guide/kernel-parameters.txt +++
> > b/Documentation/admin-guide/kernel-parameters.txt @@ -1982,6 +1982,12
> > @@ Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
> >   			the default is off.
> >   
> > +	kpti=		[ARM64] Control page table isolation of
> > user
> > +			and kernel address spaces.
> > +			Default: enabled on cores which need
> > mitigation.
>
> Would this be a good place to mention that we enable it when
> CONFIG_RANDOMIZE_BASE is enabled and we have a valid kaslr_offset? I
> found this somewhat surprising, also it's unrelated to the
> vulnerability.

Maybe, but I tend to think since this command line forces it on/off 
regardless of RANDOMIZE_BASE, that a better place to mention that 
RANDOMIZE_BASE forces kpti on is the Kconfig option.

BTW: Thanks for reviewing this.


> Cheers,
> Andre
>
> > +			0: force disabled
> > +			1: force enabled
> > +
> >   	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled
> > MSRs. Default is 0 (don't ignore, but inject #GP)
> >