Re: [Xen-devel] [PATCH v5 0/4] x86: modify_ldt improvement, test, and config option

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/30/2015 01:06 PM, Andrew Cooper wrote:
> On 30/07/15 17:31, Boris Ostrovsky wrote:
> > On 07/30/2015 12:12 PM, Andrew Cooper wrote:
> > > On 30/07/15 17:05, Borislav Petkov wrote:
> > > > On Thu, Jul 30, 2015 at 11:53:34AM -0400, Boris Ostrovsky wrote:
> > > > > As far as Xen guests are concerned,
> > > > >
> > > > > Tested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > > > Does that mean, this patch 1/4 fixes the 32bit issue you guys are still
> > > > debugging on the v4 thread? Or does that need more fixing?
> > > I was going to say... This v5 pre-dates figuring out what was wrong with
> > > 32bit Xen.  v5 1/4 is still susceptible.
> > >
> > > Boris: does your Tested-by cover v5 + proposed fix?
> > Only V5, no extra changes.
> Including running the ldt_gdt test?
Yes, except that 32-on-64 doesn't work, but that's not Xen-specific.

Still, user-visible behavior changes.

> > And perhaps dropping aliases in xen_alloc_ldt() may be sufficient
> > since with that done we will only have one mapping so a subsequent
> > fault will have "correct" cr2 provided by the hypervisor (from your
> > earlier email it sounded that hypervisor may have been providing
> > incorrect cr2 if alias exists)
> They are sufficient to fix the first of the two bugs, but the free side
> still has no protection against a missing l2, unless I am missing
> something in the rest of the series?
Without aliases a subsequent fault *will* fill correct l2, won't it?

-boris

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