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

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Date:	Tue, 15 Dec 2015 10:40:15 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	kernel list <linux-kernel@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Peter Anvin <hpa@...or.com>, Mike Galbraith <efault@....de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 4.4-rc5: ugly warn on: 5 W+X pages found

On Mon 2015-12-14 14:25:10, Andy Lutomirski wrote:
> On Mon, Dec 14, 2015 at 1:24 PM, Arjan van de Ven <arjan@...ux.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).

I tried applying:

[PATCH 1/2] x86_32/mm: Set NX in __supported_pte_mask before enabling
paging

but I still get

[    2.685402] ------------[ cut here ]------------
[    2.688649] WARNING: CPU: 0 PID: 1 at
arch/x86/mm/dump_pagetables.c:225 note_
page+0x5ec/0x790()
[    2.691897] x86/mm: Found insecure W+X mapping at address
ffe69000/0xffe69000
[    2.695090] Modules linked in:

Best regards,
									Pavel

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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