linux-kernel - Re: [patch 57/60] x86/mm/kpti: Add Kconfig

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Date:   Mon, 4 Dec 2017 08:54:57 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, moritz.lipp@...k.tugraz.at,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Borislav Petkov <bp@...en8.de>, michael.schwarz@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [patch 57/60] x86/mm/kpti: Add Kconfig

On Mon, Dec 4, 2017 at 6:08 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Finally allow CONFIG_KERNEL_PAGE_TABLE_ISOLATION to be enabled.
>
> PARAVIRT generally requires that the kernel not manage its own page tables.
> It also means that the hypervisor and kernel must agree wholeheartedly
> about what format the page tables are in and what they contain.
> KERNEL_PAGE_TABLE_ISOLATION, unfortunately, changes the rules and they
> can not be used together.
>
> I've seen conflicting feedback from maintainers lately about whether they
> want the Kconfig magic to go first or last in a patch series.  It's going
> last here because the partially-applied series leads to kernels that can
> not boot in a bunch of cases.  I did a run through the entire series with
> CONFIG_KERNEL_PAGE_TABLE_ISOLATION=y to look for build errors, though.
>
> [ tglx: Removed SMP and !PARAVIRT dependencies as they not longer exist ]
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: keescook@...gle.com
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: moritz.lipp@...k.tugraz.at
> Cc: linux-mm@...ck.org
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: hughd@...gle.com
> Cc: daniel.gruss@...k.tugraz.at
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: michael.schwarz@...k.tugraz.at
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: richard.fellner@...dent.tugraz.at
> Link: https://lkml.kernel.org/r/20171123003524.88C90659@viggo.jf.intel.com
>
> ---
>  security/Kconfig |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -54,6 +54,16 @@ config SECURITY_NETWORK
>           implement socket and networking access controls.
>           If you are unsure how to answer this question, answer N.
>
> +config KERNEL_PAGE_TABLE_ISOLATION
> +       bool "Remove the kernel mapping in user mode"
> +       depends on X86_64 && JUMP_LABEL

select JUMP_LABEL perhaps?

> +       help
> +         This feature reduces the number of hardware side channels by
> +         ensuring that the majority of kernel addresses are not mapped
> +         into userspace.
> +
> +         See Documentation/x86/pagetable-isolation.txt for more details.
> +
>  config SECURITY_INFINIBAND
>         bool "Infiniband Security Hooks"
>         depends on SECURITY && INFINIBAND
>
>