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Date: Tue, 9 Apr 2013 11:54:15 -0700
Message-ID: <CAG7+5M3==rndLLak9cZBKKdgQMmJMpSP_jpQd8HOVGp6LhUAgw@mail.gmail.com>
Subject: Re: [kernel-hardening] Re: [PATCH] x86: make IDT read-only
From: Eric Northup <digitaleric@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
        "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
        Ingo Molnar <mingo@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        Marcelo Tosatti <mtosatti@redhat.com>, Alex Shi <alex.shi@intel.com>,
        Borislav Petkov <borislav.petkov@amd.com>,
        Alexander Duyck <alexander.h.duyck@intel.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
        "virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
        Dan Rosenberg <drosenberg@vsecurity.com>,
        Julien Tinnes <jln@google.com>, Will Drewry <wad@chromium.org>
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On Tue, Apr 9, 2013 at 11:46 AM, Kees Cook <keescook@chromium.org> wrote:
> On Tue, Apr 9, 2013 at 11:39 AM, H. Peter Anvin <hpa@zytor.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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