Re: [PATCH] x86/mm: Unbreak modules that rely on external PAGE_KERNEL availability

[Tom Lendacky]

On 11/8/2017 3:23 PM, Linus Torvalds wrote:
> On Wed, Nov 8, 2017 at 1:15 PM, Borislav Petkov <bp@xxxxxxx> 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