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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 14 Dec 2015 14:25:10 -0800
Message-ID: <CALCETrW60DfZs-v_W46sYFUmBXspa3BXWY-=dpuSF9iMaeLGFQ@mail.gmail.com>
Subject: Re: 4.4-rc5: ugly warn on: 5 W+X pages found
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Pavel Machek <pavel@ucw.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        kernel list <linux-kernel@vger.kernel.org>,
        Stephen Smalley <sds@tycho.nsa.gov>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Mike Galbraith <efault@gmx.de>, Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
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On Mon, Dec 14, 2015 at 1:24 PM, Arjan van de Ven <arjan@linux.intel.com> 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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