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

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Message-ID: <CALCETrX6DrW2AJz=WGjMW+nNTsq08+Cte0m=CF_Q9+uzsuR1vA@mail.gmail.com>
Date:	Mon, 14 Dec 2015 13:02:27 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	kernel list <linux-kernel@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	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, Dec 14, 2015 at 12:26 PM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
>> > I know. But either someone cares, and it should be fixes, or noone
>> > cares, and the check should be removed.
>>
>> Someone cares, and it should be scheduled to be fixed for 4.5. The EFI
>> mapping changes that were required to avoid the warning were much too
>> big and late to make 4.4.
>>
>> So for now, don't enable CONFIG_DEBUG_WX for now. Unless you want to
>> actively debug the EFI mapping changes, that is. Which I heartily
>> recommend people doing.
>
> Ok, good, except... This is thinkpad X60. Good old BIOS. It should
> have no EFI.
>
> pavel@duo:~$ dmesg | grep EFI
> pavel@duo:~$
>
> From the messages I got:
>
>> [    3.285993] x86/mm: Found insecure W+X mapping at address
>> ffe69000/0xffe69000
>
> ---[ Persisent kmap() Area ]---
> 0xffc00000-0xffd28000        1184K                               pte
> 0xffd28000-0xffddd000         724K     RW                 GLB NX pte
> 0xffddd000-0xffe69000         560K                               pte
> 0xffe69000-0xffe6e000          20K     RW                 GLB x  pte
> 0xffe6e000-0xffe6f000           4K                               pte
> ---[ Fixmap Area ]---
>
> That is not EFI, right?

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?

--Andy
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