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

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Date:   Mon, 8 May 2017 16:19:29 +0200
From:   Daniel Gruss <daniel.gruss@...k.tugraz.at>
To:     Thomas Garnier <thgarnie@...gle.com>
CC:     David Gens <david.gens@...tu-darmstadt.de>,
        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 08.05.2017 16:09, Thomas Garnier wrote:
>> 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.
>
> Why do you think it should be at a fixed location in the user CR3? I
> see that you just mirror the entries. You also mirror
> __entry_text_start / __entry_text_end which is part of the binary so
> will leak the base address of the kernel. Maybe I am missing
> something.

As I said, the current patch does not incorporate this yet, so yes, this part currently still leaks because we did not 
implement it yet.