linux-kernel - Re: [RFC/GIT PULL] Linux KVM tool for v3.2

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Message-ID: <CA+1xoqc7f-2azcjuLB_i_C_CCDt+gPqJe=SB5MmOiM0y6uY_cg@mail.gmail.com>
Date:	Thu, 10 Nov 2011 11:04:46 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Markus Armbruster <armbru@...hat.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [RFC/GIT PULL] Linux KVM tool for v3.2

On Thu, Nov 10, 2011 at 10:57 AM, Markus Armbruster <armbru@...hat.com> wrote:
> Sasha Levin <levinsasha928@...il.com> writes:
>
>> On Thu, Nov 10, 2011 at 9:57 AM, Markus Armbruster <armbru@...hat.com> wrote:
> [...]
>>> Start with a clean read/write raw image.  Probing declares it raw.
>>> Guest writes QCOW signature to it, with a backing file of its choice.
>>>
>>> Restart with the same image.  Probing declares it QCOW2.  Guest can read
>>> the backing file.  Oops.
>>
>> Thats an excellent scenario why you'd want to have 'Secure KVM' with
>> seccomp filters :)
>
> Yup.
>
> For what it's worth, sVirt (use SELinux to secure virtualization)
> mitigates the problem.  Doesn't mean we couldn't use "Secure KVM".

How does it do it do that? You have a hypervisor trying to read
arbitrary files on the host FS, no?

>> I'm actually not sure why KVM tool got QCOW support in the first
>> place. You can have anything QCOW provides if you use btrfs (among
>> several other FSs).
>
> Maybe it's just me, but isn't it weird to have a filesystem (QCOW2)
> sitting in the kernel sources that you can't mount(2)?
>

It's not really a filesystem, it's a disk image :)

When we did the initial QCOW patches this issue (in some form) came
up. The main concern there was that we shouldn't be duplicating QCOW
code and instead be using a 'libdiskimage' or something like that.

Since nothing like that existed at that time, and splitting it out of
QEMU wasn't trivial, we ended up agreeing on doing a rewrite of the
code.

The point you raised could be solved if we do end up having a usermode
lib which can handle disk images.
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