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 15:02:52 +0100
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:	Stephen Smalley <sds@...ho.nsa.gov>, 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


Thursday, November 5, 2015, 2:53:40 PM, you wrote:

> 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

Ah thx for the pointer :)

--
Sander




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