linux-kernel - Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for memory encryption

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Date:   Mon, 12 Sep 2016 08:43:14 -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>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for
 memory encryption

On 09/08/2016 08:55 AM, Borislav Petkov wrote:
> On Thu, Sep 08, 2016 at 08:26:27AM -0500, Tom Lendacky wrote:
>> When does this value get initialized?  Since _PAGE_ENC is #defined to
>> sme_me_mask, which is not set until the boot process begins, I'm afraid
>> we'd end up using the initial value of sme_me_mask, which is zero.  Do
>> I have that right?
> 
> Hmm, but then that would hold true for all the other defines where you
> OR-in _PAGE_ENC, no?

As long as the #define is not a global variable like this one it's ok.

> 
> In any case, the preprocessed source looks like this:
> 
> pmdval_t early_pmd_flags = (((((((pteval_t)(1)) << 0) | (((pteval_t)(1)) << 1) | (((pteval_t)(1)) << 6) | (((pteval_t)(1)) << 5) | (((pteval_t)(1)) << 8)) | (((pteval_t)(1)) << 63)) | (((pteval_t)(1)) << 7)) | sme_me_mask) & ~((((pteval_t)(1)) << 8) | (((pteval_t)(1)) << 63));
> 
> but the problem is later, when building:
> 
> arch/x86/kernel/head64.c:39:28: error: initializer element is not constant
>  pmdval_t early_pmd_flags = (__PAGE_KERNEL_LARGE | _PAGE_ENC) & ~(_PAGE_GLOBAL | _PAGE_NX);
>                             ^
> scripts/Makefile.build:153: recipe for target 'arch/x86/kernel/head64.s' failed
> 
> so I guess not. :-\
> 
> Ok, then at least please put the early_pmd_flags init after
> sme_early_init() along with a small comment explaning what happens.

Let me verify that we won't possibly take any kind of page fault during
sme_early_init() and cause a page to be not be marked encrypted. Or... I
can add a comment indicating I need to set this as early as possible to
cover any page faults that might occur.

Thanks,
Tom

> 
> Thanks.
>