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Date: Fri, 5 Apr 2013 15:13:37 -0700
Message-ID: <CAKyRK=j2UyqQFT2AEX5QqEA335n7r2pgJmK52in924x8LFNbTA@mail.gmail.com>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR
From: Julien Tinnes <jln@google.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>, Kees Cook <keescook@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "x86@kernel.org" <x86@kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@intel.com>,
        Matthew Garrett <mjg@redhat.com>,
        Matt Fleming <matt.fleming@intel.com>,
        Eric Northup <digitaleric@google.com>,
        Dan Rosenberg <drosenberg@vsecurity.com>,
        Will Drewry <wad@chromium.org>
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On Fri, Apr 5, 2013 at 3:08 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 04/05/2013 03:06 PM, Julien Tinnes wrote:
>>
>> Speaking of IDT, and to capture some off-thread discussion here, we
>> should remember that the "SGDT" and "SIDT" instructions aren't
>> privileged on x86, so user-land can leak these out without any way for
>> the kernel to intercept that.
>>
>> Adding their own random offsets to these two tables would be very
>> useful. This could be done in a later patchset of course.
>>
>
> Yes, if the GDT or IDT position is at all correlated to the kernel
> position this is pointless.

Let's say it's less useful :) Remote attacks and from-inside-a-VM
attack would still be mitigated.

Julien
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