linux-kernel - Re: [discussion] proposal to bypass zero data for dm-crypt

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] [day] [month] [year] [list]

Message-ID: <cb49d8ca786fd0e51947e83e74036a6c00f75e2e.camel@HansenPartnership.com>
Date: Mon, 06 Jan 2025 18:04:54 -0800
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Alasdair Kergon <agk@...hat.com>, 
 Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka <mpatocka@...hat.com>,
 dm-devel@...ts.linux.dev, lkml <linux-kernel@...r.kernel.org>, "yukuai (C)"
 <yukuai3@...wei.com>
Subject: Re: [discussion] proposal to bypass zero data for dm-crypt

On Sat, 2024-12-21 at 10:34 +0800, Yu Kuai wrote:
> Background
> 
> We provide virtual machines for customers to use, which include an 
> important feature: in the initial state, the disks in the virtual 
> machine do not occupy actual storage space, and the data read by
> users is all zeros until the user writes data for the first time.
> This can save a large amount of storage.
> 
> Problem
> 
> However, after introducing dm-crypt, this feature has failed. Because
> we expect the data read by users in the initial state to be zero, we
> have to write all zeros from dm-crypt.

Why do you expect the user to read all zeros?  For DM crypt on a new
physical disk, we don't set the disk contents to an initial value
because there's no expectation on the part of the user that they can
read a sector they haven't written and get a sensible result instead of
the dm-crypt of whatever the sector contained.  Why can't your cloud
system just behave like a physical disk?

Even for an unencrypted physical disk, there's no expectation of any
particular value being in a sector, so why do your users have the
expectation of all zeros?

Regards,

James