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

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Message-ID: <dd7fd5dd-8038-a871-bdee-7b253078b933@iaik.tugraz.at>
Date:   Sat, 6 May 2017 10:28:30 +0200
From:   Daniel Gruss <daniel.gruss@...k.tugraz.at>
To:     Jann Horn <jannh@...gle.com>
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: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map
 kernel in user mode

On 2017-05-05 17:53, Jann Horn wrote:
> Ah, I think I understand. The kernel stacks are mapped, but
> cpu_current_top_of_stack isn't, so you can't find the stack until after the CR3
> switch in the syscall handler?

That's the idea. Only the absolute minimum that is required for a 
context switch remains mapped (+ it is mapped at an offset which does 
not depend on KASLR -> we do not leak the KASLR offsets).