linux-kernel - Re: [PATCH 3/3] x86: kernel base offset ASLR

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Message-ID: <CAKyRK=j2UyqQFT2AEX5QqEA335n7r2pgJmK52in924x8LFNbTA@mail.gmail.com>
Date:	Fri, 5 Apr 2013 15:13:37 -0700
From:	Julien Tinnes <jln@...gle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Eric Northup <digitaleric@...gle.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR

On Fri, Apr 5, 2013 at 3:08 PM, H. Peter Anvin <hpa@...or.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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