linux-kernel - Re: [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <565468ED.8060206@citrix.com>
Date:	Tue, 24 Nov 2015 13:41:01 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>, Petr Tesarik <ptesarik@...e.cz>
CC:	Juergen Gross <JGross@...e.com>, <olaf@...fle.de>, <keir@....org>,
	DanielKiper <daniel.kiper@...cle.com>,
	<linux-kernel@...r.kernel.org>, <dslutz@...izon.com>,
	<anderson@...hat.com>, David Vrabel <david.vrabel@...rix.com>,
	David Mair <DMAIR@...e.com>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>,
	"Malcolm Crossley" <malcolm.crossley@...rix.com>,
	<crash-utility@...hat.com>
Subject: Re: [Xen-devel] crash tool - problem with new Xen linear virtual
 mapped sparse p2m list

On 24/11/15 13:39, Jan Beulich wrote:
>>>> On 24.11.15 at 13:57, <ptesarik@...e.cz> wrote:
>> V Tue, 24 Nov 2015 10:35:03 +0000
>> Andrew Cooper <andrew.cooper3@...rix.com> napsáno:
>>
>>> On 24/11/15 10:17, Petr Tesarik wrote:
>>>> On Tue, 24 Nov 2015 10:09:01 +0000
>>>> David Vrabel <david.vrabel@...rix.com> wrote:
>>>>
>>>>> On 24/11/15 09:55, Malcolm Crossley wrote:
>>>>>> On 24/11/15 08:59, Jan Beulich wrote:
>>>>>>>>>> On 24.11.15 at 07:55, <JGross@...e.com> wrote:
>>>>>>>> What about:
>>>>>>>>
>>>>>>>> 4) Instead of relying on the kernel maintained p2m list for m2p
>>>>>>>>    conversion use the hypervisor maintained m2p list which should be
>>>>>>>>    available in the dump as well. This is the way the alive kernel is
>>>>>>>>    working, so mimic it during crash dump analysis.
>>>>>>> I fully agree; I have to admit that looking at the p2m when doing page
>>>>>>> table walks for a PV Dom0 (having all machine addresses in page table
>>>>>>> entries) seems kind of backwards. (But I say this knowing nothing
>>>>>>> about the tool.)
>>>>>>>
>>>>>> I don't think we can reliably use the m2p for PV domains because
>>>>>> PV domains don't always issue a m2p update hypercall when they change
>>>>>> their p2m mapping.
>>>>> This only applies to foreign pages which won't be very interesting to a
>>>>> crash tool.
>>>> True. I think the main reason crash hasn't done this is that it cannot
>>>> find the hypervisor maintained m2p list. It should be sufficient to add
>>>> some more fields to XEN_VMCOREINFO, so that crash can locate the
>>>> mapping in the dump.
>>> The M2P lives at an ABI-specified location in all virtual address spaces
>>> for PV guests.
>>>
>>> Either 0xF5800000 or 0xFFFF800000000000 depending on bitness.
>> Hm, this is nice, but kind of chicken-and-egg problem. A system dump
>> contains a snapshot of the machine's RAM. But the addresses you
>> mentioned are virtual addresses. How do I translate them to physical
>> addresses without an m2p mapping? I need at least the value of CR3 for
>> that domain, and most likely a way to determine if it is a PV domain.
> This ought to also be present in Xen's master page table
> (idle_pg_table[]), and I suppose we can take for granted a symbol
> table being available.

The idle_pg_table is already present in the VMCORE notes.

~Andrew
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/