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Date: Thu, 30 Jul 2015 18:06:57 +0100
From: Andrew Cooper <andrew.cooper3@citrix.com>
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To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>
CC: "security@kernel.org" <security@kernel.org>,
        Jan Beulich <jbeulich@suse.com>, Peter Zijlstra <peterz@infradead.org>,
        X86 ML <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        xen-devel <xen-devel@lists.xen.org>, Andy Lutomirski <luto@kernel.org>,
        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: [Xen-devel] [PATCH v5 0/4] x86: modify_ldt improvement, test,
 and config option
References: <cover.1438061139.git.luto@kernel.org>
	<55BA487E.9030708@oracle.com> <20150730160555.GB28617@nazgul.tnic>
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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@oracle.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