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Date: Thu, 4 May 2017 08:28:52 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Daniel Gruss <daniel.gruss@...k.tugraz.at>
Cc: kernel list <linux-kernel@...r.kernel.org>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>, 
	"clementine.maurice@...k.tugraz.at" <clementine.maurice@...k.tugraz.at>, 
	"moritz.lipp@...k.tugraz.at" <moritz.lipp@...k.tugraz.at>, 
	Michael Schwarz <michael.schwarz@...k.tugraz.at>, 
	Richard Fellner <richard.fellner@...dent.tugraz.at>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>, 
	"anders.fogh@...ta-adan.de" <anders.fogh@...ta-adan.de>
Subject: Re: [RFC, PATCH] x86_64: KAISER - do not map
 kernel in user mode

On Thu, May 4, 2017 at 3:02 AM, Daniel Gruss
<daniel.gruss@...k.tugraz.at> wrote:
> After several recent works [1,2,3] KASLR on x86_64 was basically considered
> dead by many researchers. We have been working on an efficient but effective
> fix for this problem and found that not mapping the kernel space when
> running in user mode is the solution to this problem [4] (the corresponding
> paper [5] will be presented at ESSoS17).
>
> With this RFC patch we allow anybody to configure their kernel with the flag
> CONFIG_KAISER to add our defense mechanism.
>
> If there are any questions we would love to answer them.
> We also appreciate any comments!
>
> Cheers,
> Daniel (+ the KAISER team from Graz University of Technology)
>
> [1] http://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf
> [2]
> https://www.blackhat.com/docs/us-16/materials/us-16-Fogh-Using-Undocumented-CPU-Behaviour-To-See-Into-Kernel-Mode-And-Break-KASLR-In-The-Process.pdf
> [3]
> https://www.blackhat.com/docs/us-16/materials/us-16-Jang-Breaking-Kernel-Address-Space-Layout-Randomization-KASLR-With-Intel-TSX.pdf
> [4] https://github.com/IAIK/KAISER
> [5] https://gruss.cc/files/kaiser.pdf
>
>

Please read the documentation on submitting patches [1] and coding style [2].

I have two questions:

 - How this approach prevent the hardware attacks you mentioned? You
still have to keep a part of _text in the pagetable and an attacker
could discover it no? (and deduce the kernel base address). You also
need to make it clear that btb attacks are still possible.
 - What is the perf impact?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst

Thanks,
-- 
Thomas

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