linux-kernel - Re: [patch 23/60] x86/entry/64: Make cpu_entry

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Message-ID: <20171204202552.rnadiic5dxvwt4q3@pd.tnic>
Date:   Mon, 4 Dec 2017 21:25:53 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, 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>,
        Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com,
        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@...k.tugraz.at,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 23/60] x86/entry/64: Make cpu_entry_area.tss read-only

On Mon, Dec 04, 2017 at 03:07:29PM +0100, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@...nel.org>
> 
> The TSS is a fairly juicy target for exploits, and, now that the TSS
> is in the cpu_entry_area, it's no longer protected by kASLR.  Make it
> read-only on x86_64.
> 
> On x86_32, it can't be RO because it's written by the CPU during task
> switches, and we use a task gate for double faults.  I'd also be
> nervous about errata if we tried to make it RO even on configurations
> without double fault handling.
> 
> [ tglx: AMD confirmed that there is no problem on 64bit with TSS RO.  So
>   	it's probably safe to assume that it's a non issue, though Intel
>   	might have been creative in that area. Still waiting for
>   	confirmation. ]
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: David Laight <David.Laight@...lab.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Link: https://lkml.kernel.org/r/7d2f65f86a46e3489ba996932554485c3d345632.1512109321.git.luto@kernel.org
> 
> ---
>  arch/x86/entry/entry_32.S          |    4 ++--
>  arch/x86/entry/entry_64.S          |    8 ++++----
>  arch/x86/include/asm/fixmap.h      |   13 +++++++++----
>  arch/x86/include/asm/processor.h   |   17 ++++++++---------
>  arch/x86/include/asm/switch_to.h   |    4 ++--
>  arch/x86/include/asm/thread_info.h |    2 +-
>  arch/x86/kernel/asm-offsets.c      |    5 ++---
>  arch/x86/kernel/asm-offsets_32.c   |    4 ++--
>  arch/x86/kernel/cpu/common.c       |   29 +++++++++++++++++++----------
>  arch/x86/kernel/ioport.c           |    2 +-
>  arch/x86/kernel/process.c          |    6 +++---
>  arch/x86/kernel/process_32.c       |    2 +-
>  arch/x86/kernel/process_64.c       |    2 +-
>  arch/x86/kernel/traps.c            |    4 ++--
>  arch/x86/lib/delay.c               |    4 ++--
>  arch/x86/xen/enlighten_pv.c        |    2 +-
>  16 files changed, 60 insertions(+), 48 deletions(-)

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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