linux-kernel - Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER

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Date:   Mon, 8 May 2017 15:53:20 +0200
From:   Daniel Gruss <daniel.gruss@...k.tugraz.at>
To:     David Gens <david.gens@...tu-darmstadt.de>,
        Thomas Garnier <thgarnie@...gle.com>
CC:     kernel list <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        <clementine.maurice@...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>
Subject: Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map
 kernel in user mode

On 06.05.2017 10:38, Daniel Gruss wrote:
> On 2017-05-06 06:02, David Gens wrote:
>> Assuming that their patch indeed leaks per-cpu addresses.. it might not
>> necessarily
>> be required to change it.
>
> I think we're not leaking them (unless we still have some bug in our code).

Just to correct my answer here as well: Although we experimented with fixed mappings for per-cpu addresses, the current 
patch does not incorporate this yet, so it indeed still leaks. However, it is not a severe problem. The mapping of the 
required (per-cpu) variables would be at a fixed location in the user CR3, instead of the ones that are used in the kernel.