linux-kernel - Re: DO NOT APPLY: x86-64, espfix: Don't leak bits 31:16 of %esp returning to 16-bit stack

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Date:	Tue, 15 Jul 2014 17:49:27 -0700
From:	Greg KH <greg@...ah.com>
To:	Andrew Lutomirski <amluto@...il.com>
Cc:	Kamal Mostafa <kamal@...onical.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>, kernel-team@...ts.ubuntu.com,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dirk Hohndel <dirk@...ndel.org>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	comex <comexk@...il.com>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: DO NOT APPLY: x86-64, espfix: Don't leak bits 31:16 of %esp
 returning to 16-bit stack

On Tue, Jul 15, 2014 at 04:56:36PM -0700, Andrew Lutomirski wrote:
> On Tue, Jul 15, 2014 at 4:52 PM, Greg KH <greg@...ah.com> wrote:
> > On Tue, Jul 15, 2014 at 04:21:46PM -0700, Andrew Lutomirski wrote:
> >> On Tue, Jul 15, 2014 at 2:28 PM, Kamal Mostafa <kamal@...onical.com> wrote:
> >> > 3.13.11.5 -stable review patch.  If anyone has any objections, please let me know.
> >> >
> >> > ------------------
> >> >
> >> > From: "H. Peter Anvin" <hpa@...ux.intel.com>
> >> >
> >> > commit 3891a04aafd668686239349ea58f3314ea2af86b upstream.
> >>
> >> Do not apply to any -stable release yet.  This causes nasty regressions on Xen.
> >
> > I thought you all found the Xen-regression-fix patch a few hours ago,
> > right?
> 
> That patch is insufficient: Xen guests still fail to initialize
> espfix64 correctly on SMP.  It's currently unclear that espfix64 can
> work at all on Xen -- it's may be rather fundamentally incompatible
> with the Xen hypercall IRET mechanism.  So it might need to be
> disabled entirely on Xen (and maybe Xen will fix the info leak in the
> hypervisor).

Ok, I'll pospone these all until the next round of stable releases next
week, Linus's tree should be fixed by then.

thanks,

greg k-h
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