Re: 4.4-rc5: ugly warn on: 5 W+X pages found

[Andy Lutomirski]

On Mon, Dec 14, 2015 at 1:24 PM, Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote:
>
>> That's weird.  The only API to do that seems to be manually setting
>> kmap_prot to _PAGE_KERNEL_EXEC, and nothing does that.  (Why is
>> kmap_prot a variable on x86 at all?  It has exactly one writer, and
>> that's the code that initializes it in the first place.  Shouldn't we
>> #define kmap_prot _PAGE_KERNEL?
>
>
> iirc it changes based on runtime detection of NX capability
>

Maybe it did, but if it still does, I can't find the code.

What *does* change is __supported_pte_mask.  If we're willing to make
disable_nx work a little less well, we could try to initialize
__supported_pte_mask from the very beginning.  (We currently seem to
detect and enable NX even before we enable paging.)  I suspect that
Pavel is seeing a kmap mapping left over from so early that it didn't
have NX set (killed by massage_pgprot).

Borislav, could we do that?  (Why do we have disable_nx at all?  I
suspect it was for debugging a long, long time ago.)

Alternatively, we could go through and set NX everywhere after we
decide we have NX, but that seems rather error-prone.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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