linux-kernel - Re: [Xen-devel] Linux 4.4 MW: Boot under Xen fails with CONFIG_DEBUG_WX enabled: RIP: ptdump_walk_pgd_level

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Date:	Thu, 5 Nov 2015 08:53:40 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Sander Eikelenboom <linux@...elenboom.it>,
	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xen.org, mingo.kernel.org@...il.com
Subject: Re: [Xen-devel] Linux 4.4 MW: Boot under Xen fails with
 CONFIG_DEBUG_WX enabled: RIP: ptdump_walk_pgd_level_core

On 11/05/2015 04:13 AM, Sander Eikelenboom wrote:
>
> It makes "cat /sys/kernel/debug/kernel_page_tables" work and
> prevents a kernel with CONFIG_DEBUG_WX=y from crashing at boot.

Great. Our nightly runs also failed spectacularly due to this bug.

>
> It now does give a warning about an insecure W+X mapping, so 
> CONFIG_DEBUG_WX=y
> seems to be working. No idea how to interpret it though (and if it's a 
> legit
> warning).
>
> -- 
> Sander
>
> [   19.034706] Freeing unused kernel memory: 1104K (ffffffff822fc000 - 
> ffffffff82410000)
> [   19.041339] Write protecting the kernel read-only data: 18432k
> [   19.052596] Freeing unused kernel memory: 1144K (ffff880001ae2000 - 
> ffff880001c00000)
> [   19.060285] Freeing unused kernel memory: 1560K (ffff88000207a000 - 
> ffff880002200000)
> [   19.067079] ------------[ cut here ]------------
> [   19.073931] WARNING: CPU: 5 PID: 1 at 
> arch/x86/mm/dump_pagetables.c:225 note_page+0x619/0x7e0()

Yes, this apparently is a known issue: https://lkml.org/lkml/2015/11/4/476

-boris


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