linux-kernel - Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory Encryption

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Date:   Wed, 31 May 2017 08:37:50 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory
 Encryption

On 5/31/2017 3:49 AM, Borislav Petkov wrote:
> On Tue, May 30, 2017 at 10:37:03AM -0500, Tom Lendacky wrote:
>> I can define the command line option and the "on" and "off" values as
>> character buffers in the function and initialize them on a per character
>> basis (using a static string causes the same issues as referencing a
>> string constant), i.e.:
>>
>> char cmdline_arg[] = {'m', 'e', 'm', '_', 'e', 'n', 'c', 'r', 'y', 'p', 't', '\0'};
>> char cmdline_off[] = {'o', 'f', 'f', '\0'};
>> char cmdline_on[] = {'o', 'n', '\0'};
>>
>> It doesn't look the greatest, but it works and removes the need for the
>> rip-relative addressing.
> 
> Well, I'm not thrilled about this one either. It's like being between a
> rock and a hard place. :-\
> 
> On the one hand, we need the encryption mask before we do the fixups and
> OTOH we need to do the fixups in order to access the strings properly.
> Yuck.
> 
> Well, the only thing I can think of right now is maybe define
> "mem_encrypt=" at the end of head_64.S and pass it in from asm to
> sme_enable() and then do the "on"/"off" comparsion with local char
> buffers. That could make it less ugly...

I like keeping the command line option and the values together. It may
not look the greatest but I like it more than defining the command line
option in head_64.S and passing it in as an argument.

OTOH, I don't think the rip-relative addressing was that bad, I can
always go back to that...

Thanks,
Tom

>