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Date: Thu, 4 May 2017 08:28:52 -0700
From: Thomas Garnier <>
To: Daniel Gruss <>
Cc: kernel list <>, 
	Kernel Hardening <>, 
	"" <>, 
	"" <>, 
	Michael Schwarz <>, 
	Richard Fellner <>, 
	"Kirill A. Shutemov" <>, Ingo Molnar <>, 
	"" <>
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
<> 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]
> [2]
> [3]
> [4]
> [5]

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?



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