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Message-ID: <CAG7+5M3==rndLLak9cZBKKdgQMmJMpSP_jpQd8HOVGp6LhUAgw@mail.gmail.com>
Date: Tue, 9 Apr 2013 11:54:15 -0700
From: Eric Northup <digitaleric@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: "H. Peter Anvin" <hpa@...or.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Jeremy Fitzhardinge <jeremy@...p.org>,
Marcelo Tosatti <mtosatti@...hat.com>, Alex Shi <alex.shi@...el.com>,
Borislav Petkov <borislav.petkov@....com>, Alexander Duyck <alexander.h.duyck@...el.com>,
Frederic Weisbecker <fweisbec@...il.com>, Steven Rostedt <rostedt@...dmis.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
Dan Rosenberg <drosenberg@...curity.com>, Julien Tinnes <jln@...gle.com>,
Will Drewry <wad@...omium.org>
Subject: Re: Re: [PATCH] x86: make IDT read-only
On Tue, Apr 9, 2013 at 11:46 AM, Kees Cook <keescook@...omium.org> wrote:
> On Tue, Apr 9, 2013 at 11:39 AM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 04/09/2013 11:31 AM, Kees Cook wrote:
>>>>> ...
>>>>> 0xffff880001e00000-0xffff88001fe00000 480M RW PSE GLB NX pmd
>>>>>
>>>>
>>>> That is the 1:1 memory map area...
>>>
>>> Meaning what?
>>>
>>> -Kees
>>>
>>
>> That's the area in which we just map 1:1 to memory. Anything allocated
>> with e.g. kmalloc() ends up with those addresses.
>
> Ah-ha! Yes, I see now when comparing the debug/kernel_page_tables
> reports. It's just the High Kernel Mapping that we care about.
> Addresses outside that range are less of a leak. Excellent, then GDT
> may not be a problem. Whew.
The GDT is a problem if the address returned by 'sgdt' is
kernel-writable - it doesn't necessarily reveal the random offset, but
I'm pretty sure that writing to the GDT could cause privilege
escalation.
>
> Does the v2 IDT patch look okay, BTW?
>
> -Kees
>
> --
> Kees Cook
> Chrome OS Security
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