linux-kernel - Re: [PATCH v5 29/32] x86/mm: Add support to encrypt the kernel in-place

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Date:   Tue, 30 May 2017 11:39:07 -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 29/32] x86/mm: Add support to encrypt the kernel
 in-place

On 5/26/2017 11:25 AM, Borislav Petkov wrote:
> On Thu, May 25, 2017 at 05:24:27PM -0500, Tom Lendacky wrote:
>> I guess I could do that, but this will probably only end up clearing a
>> single PGD entry anyway since it's highly doubtful the address range
>> would cross a 512GB boundary.
> 
> Or you can compute how many 512G-covering, i.e., PGD entries there are
> and clear just the right amnount. :^)
> 
>> I can change the name. As for the use of ENTRY... without the
>> ENTRY/ENDPROC combination I was receiving a warning about a return
>> instruction outside of a callable function. It looks like I can just
>> define the "sme_enc_routine:" label with the ENDPROC and the warning
>> goes away and the global is avoided. It doesn't like the local labels
>> (.L...) so I'll use the new name.
> 
> Is that warning from objtool or where does it come from?

Yes, it's from objtool:

arch/x86/mm/mem_encrypt_boot.o: warning: objtool: .text+0xd2: return 
instruction outside of a callable function

> 
> How do I trigger it locally

I think having CONFIG_STACK_VALIDATION=y will trigger it.

> 
>> The hardware will try to optimize rep movsb into large chunks assuming
>> things are aligned, sizes are large enough, etc. so we don't have to
>> explicitly specify and setup for a rep movsq.
> 
> I thought the hw does that for movsq too?

It does.

Thanks,
Tom

>