linux-kernel - Re: [PATCH] x86: add UMIP support

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Date:   Thu, 17 Nov 2016 07:52:13 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Stas Sergeev <stsp@...t.ru>
Subject: Re: [PATCH] x86: add UMIP support


* Jan Beulich <JBeulich@...e.com> wrote:

> This is a small aid to security, hiding in particular the kernel address
> information otherwise available through SGDT/SIDT.
> 
> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> ---
> Main question here is whether to limit this to 64-bit (or at least
> !CONFIG_VM86) for the time being, or to disable it while running VM86
> mode code: Such code isn't unlikely to use SMSW (and one of SGDT/SIDT)
> to figure out whether it's running on an i286 or i386, as the EFLAGS
> based method recommended by Intel's SDM can't be relied upon there.
> ---
>  Documentation/kernel-parameters.txt         |    4 ++++
>  arch/x86/include/asm/cpufeatures.h          |    1 +
>  arch/x86/include/uapi/asm/processor-flags.h |    2 ++
>  arch/x86/kernel/cpu/common.c                |   16 +++++++++++++++-
>  4 files changed, 22 insertions(+), 1 deletion(-)

Note that similar patches have been submitted a week ago:

  https://lkml.org/lkml/2016/11/8/68

Thanks,

	Ingo