linux-kernel - Re: [RFC PATCH v4 27/28] x86: Add support to encrypt the kernel in-place

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Message-ID: <20170302185151.nllxa4hty3tukfkr@pd.tnic>
Date:   Thu, 2 Mar 2017 19:51:51 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.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>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 27/28] x86: Add support to encrypt the kernel
 in-place

On Thu, Mar 02, 2017 at 12:30:31PM -0600, Tom Lendacky wrote:
> The "* 2" here and above is that a PUD and a PMD is needed for both
> the encrypted and decrypted mappings. I'll add a comment to clarify
> that.

Ah, makes sense. Definitely needs a comment.

> Yup, I can do that here too (but need PGDIR_SIZE).

Right, I did test and wanted to write PGDIR_SIZE but then ... I guess
something distracted me :-)

> So next_page is the first free page within the workarea in which a
> pagetable entry (PGD, PUD or PMD) can be created when we are populating
> the new mappings or adding the workarea to the current mapping.  Any
> new pagetable structures that are created will use this value.

Ok, so I guess this needs an overview comment with maybe some ascii
showing how workarea, exec_size, full_size and all those other things
play together.

> Ok, I'll work on the comment.  Something along the line of:
>
> /*
>  * The encrypted mapping of the kernel will use identity mapped
>  * virtual addresses.  A different PGD index/entry must be used to
>  * get different pagetable entries for the decrypted mapping.
>  * Choose the next PGD index and convert it to a virtual address
>  * to be used as the base of the mapping.

Better.

> Except the workarea size includes both the encryption execution
> size and the pagetable structure size.  I'll work on this to try
> and clarify it better.

That's a useful piece of info, yap, the big picture could use some more
explanation.

> Most definitely.  I appreciate the feedback since I'm very close to
> the code and have an understanding of what I'm doing. I'd like to be
> sure that everyone can easily understand what is happening.

Nice!

Thanks.

-- 
Regards/Gruss,
    Boris.

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