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

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Message-ID: <CAJcbSZEEUMSfeyAGQm8Daaaa1WEptW46rN_nCSpq-WR9dowr1Q@mail.gmail.com>
Date:   Mon, 8 May 2017 07:09:45 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Daniel Gruss <daniel.gruss@...k.tugraz.at>
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 Mon, May 8, 2017 at 6:53 AM, Daniel Gruss
<daniel.gruss@...k.tugraz.at> wrote:
> 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.

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.

-- 
Thomas