linux-kernel - Re: [PATCH] x86/mm: Unbreak modules that rely on external PAGE

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Date:   Wed, 8 Nov 2017 15:36:31 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jiri Kosina <jikos@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Greg KH <greg@...ah.com>
Subject: Re: [PATCH] x86/mm: Unbreak modules that rely on external PAGE_KERNEL
 availability

On 11/8/2017 3:23 PM, Linus Torvalds wrote:
> On Wed, Nov 8, 2017 at 1:15 PM, Borislav Petkov <bp@...e.de> wrote:
>>
>> Right, AFAIRC, the main reason for this being an export was because if
>> we hid it in a function, you'd have all those function calls as part of
>> the _PAGE_* macros and that's just crap.
> 
> Yes, that would be worse.
> 
> I was thinking that maybe we could have a fixed "encrypt" bit in our
> PTE, and then replace that "software bit" with whatever the real
> hardware mask is (if any).
> 
> Because it's nasty to have these constants that _used_ to be
> constants, and still _look_ like constants, suddely do stupid memory
> reads from random kernel data.
> 
> So _this_ is the underflying problem:
> 
>    #define _PAGE_ENC  (_AT(pteval_t, sme_me_mask))
> 
> because that is simply not how the _PAGE_xyz macros should work!
> 
> So it should have been a fixed bit to begin with, and the dynamic part
> should have been elsewhere.
> 
> The whole EXPORT_SYMBOL() thing is just a symptom of that fundamental
> error. Modules - GPL or not - should _never_ have to know or care
> about this _PAGE_ENC bit madness, simply because it shouldn't have
> been there.

I'll look into that and see what I can come up with.

Thanks,
Tom

> 
>                 Linus
>