linux-kernel - Re: [GIT PULL] x86/mm changes for v4.4

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Date:	Wed, 4 Nov 2015 18:39:07 -0500
From:	Dave Jones <davej@...emonkey.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [GIT PULL] x86/mm changes for v4.4

On Wed, Nov 04, 2015 at 11:26:12AM -0800, Linus Torvalds wrote:
 > On Tue, Nov 3, 2015 at 3:16 AM, Ingo Molnar <mingo@...nel.org> wrote:
 > >
 > > The new CONFIG_DEBUG_WX=y warning is marked default-y if CONFIG_DEBUG_RODATA=y is
 > > already eanbled, as a special exception, as these bugs are hard to notice and this
 > > check already found several live bugs.
 > 
 > So this seems to be not very useful.
 > 
 >   ...
 >   Freeing unused kernel memory: 1068K (ffffffff8bcc0000 -
 > ffffffff8bdcb000)
 >   Write protecting the kernel read-only data: 12288k
 >   Freeing unused kernel memory: 1944K (ffff88000b61a000 - ffff88000b800000)
 >   Freeing unused kernel memory: 1372K (ffff88000baa9000 - ffff88000bc00000)
 >   ------------[ cut here ]------------
 >   WARNING: CPU: 7 PID: 1 at arch/x86/mm/dump_pagetables.c:225
 > note_page+0x5dc/0x780()
 >   x86/mm: Found insecure W+X mapping at address
 > ffff88000005f000/0xffff88000005f000
 >   ...
 >   x86/mm: Checked W+X mappings: FAILED, 165660 W+X pages found.
 >   ...
 > 
 > because it doesn't seem to give you any idea where to look for the
 > issue. Those 165660 pages come out to 647MB. Odd number.
 > 
 > Is this *supposed* to come out clean?

FWIW I'm seeing this too.

[    3.293503] x86/mm: Found insecure W+X mapping at address ffff880000800000/0xffff880000800000

Looking further up the dmesg I see that range is..

[    0.468368] ---[ Low Kernel Mapping ]---
[    0.468381] 0xffff880000000000-0xffff880000800000           8M     RW                 GLB NX pte
[    0.468391] 0xffff880000800000-0xffff880000900000           1M     RW                 GLB x  pte

Linus, does that match your trace too ? The 2nd low kernel mapping?

	Dave
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