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Date: Fri, 5 May 2017 17:49:15 +0200
From: Jann Horn <jannh@...gle.com>
To: Daniel Gruss <daniel.gruss@...k.tugraz.at>
Cc: kernel list <linux-kernel@...r.kernel.org>, 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.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 12:02 PM, 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!

Why do you need this SWITCH_KERNEL_CR3_NO_STACK logic? It would
make sense if the kernel stacks weren't mapped, but if they weren't mapped,
I don't see how the entry_INT80_compat entry point could work at all - the
software interrupt itself already pushes values on the kernel stack. You could
maybe work around that using some sort of trampoline stack, but I don't see
anything like that. Am I missing something?

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