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

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Message-ID: <55BA59B1.5000600@citrix.com>
Date:	Thu, 30 Jul 2015 18:06:57 +0100
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>
CC:	"security@...nel.org" <security@...nel.org>,
	Jan Beulich <jbeulich@...e.com>,
	Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	xen-devel <xen-devel@...ts.xen.org>,
	Andy Lutomirski <luto@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [Xen-devel] [PATCH v5 0/4] x86: modify_ldt improvement, test,
 and config option

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@...cle.com>
>>> 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?

>
> 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?

~Andrew
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