Re: [dm-devel] dm-verity with GPT

From: "Pra.. Dew.." <linux_learner@outlook.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: "dm-devel@redhat.com" <dm-devel@redhat.com>
Subject: Re: [dm-devel] dm-verity with GPT
Date: Mon, 19 Sep 2022 06:10:51 +0000	[thread overview]
Message-ID: <BY5PR14MB3893F484853A8B896555EE03864D9@BY5PR14MB3893.namprd14.prod.outlook.com> (raw)
In-Reply-To: <alpine.LRH.2.02.2209180604190.19406@file01.intranet.prod.int.rdu2.redhat.com>

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Thank you Mikulas. I just want to make sure I understand what you are saying. Currently we making a dm-linear, dm-verity, dm-linear target; if I understand you right you are suggesting to make it a dm-veriy, dm-linear, dm-linear target? Of course the 2nd dm-linear target will have LBAs before dm-verity target. Did I get this right?

From: Mikulas Patocka<mailto:mpatocka@redhat.com>
Sent: Sunday, September 18, 2022 3:10 AM
To: Pra.. Dew..<mailto:linux_learner@outlook.com>
Cc: dm-devel@redhat.com<mailto:dm-devel@redhat.com>
Subject: Re: [dm-devel] dm-verity with GPT

On Sat, 17 Sep 2022, Pra.. Dew.. wrote:

>
> We have a scenario for a VM where a VM is running in the host Linux
> using KVM. We want to expose verity protected rootfs to the VM. This
> rootfs clearly needs to be RO. However, we also want to expose it as a
> GPT partition. In order to do this we are attaching two small files
> before and after the rootfs. The files use linear mapping and get mapped
> to the same /dev/mapper/XX device that has a verity partition. These two
> files contain the partition mappings (primary and backup) for GPT. From
> the VMs perspective, it sees one device (/dev/mapper/xx) as a GPT device
> with rootfs.
>
> The challenge we are getting into is that dm-verity kernel
> implementation explicitly prohibits mixing linear and verity mapping and
> forces the /dev/mapper/xx device to be RO and our needs are exactly the
> opposite.
>
> Has anyone seen this scenario before? Any suggestions?
>
> Thanks

Hi

I think that you can create dm-verity target, put dm-linear on the top of
it and insert that dm-linear into the table with the other two dm-linear
targets.

Would it work this way?

Mikulas

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