linux-kernel - Re: [PATCH v7 1/4] x86/insn-eval: Add support for 64-bit kernel mode

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Date:   Thu, 2 Jan 2020 16:55:22 +0900
From:   Andy Lutomirski <luto@...capital.net>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Jann Horn <jannh@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v7 1/4] x86/insn-eval: Add support for 64-bit kernel mode



> On Jan 2, 2020, at 4:47 PM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> 
> On Thu, Dec 19, 2019 at 12:11:47AM +0100, Jann Horn wrote:
>> To support evaluating 64-bit kernel mode instructions:
>> 
>> Replace existing checks for user_64bit_mode() with a new helper that
>> checks whether code is being executed in either 64-bit kernel mode or
>> 64-bit user mode.
>> 
>> Select the GS base depending on whether the instruction is being
>> evaluated in kernel mode.
>> 
>> Signed-off-by: Jann Horn <jannh@...gle.com>
> 
> In most cases you have struct insn around (or can easily pass it down to
> the place). Why not use insn->x86_64?
> 
> 

What populates that?

FWIW, this code is a bit buggy: it gets EFI mixed mode wrong. I’m not entirely sure we care.