linux-hardening - Re: [PATCH v2 1/3] dm-inlinecrypt: Add inline encryption support

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Message-ID: <CAAdYy_=n19fT2U1KUcF+etvbLGiOgdVZ7DceBQiHqEtXcOa-Ow@mail.gmail.com>
Date: Thu, 24 Oct 2024 11:28:16 -0400
From: Adrian Vovk <adrianvovk@...il.com>
To: Geoff Back <geoff@...onlair.co.uk>
Cc: Christoph Hellwig <hch@...radead.org>, Eric Biggers <ebiggers@...nel.org>, 
	Md Sadre Alam <quic_mdalam@...cinc.com>, axboe@...nel.dk, song@...nel.org, 
	yukuai3@...wei.com, agk@...hat.com, snitzer@...nel.org, 
	Mikulas Patocka <mpatocka@...hat.com>, adrian.hunter@...el.com, quic_asutoshd@...cinc.com, 
	ritesh.list@...il.com, ulf.hansson@...aro.org, andersson@...nel.org, 
	konradybcio@...nel.org, kees@...nel.org, gustavoars@...nel.org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-raid@...r.kernel.org, dm-devel@...ts.linux.dev, 
	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-hardening@...r.kernel.org, quic_srichara@...cinc.com, 
	quic_varada@...cinc.com
Subject: Re: [PATCH v2 1/3] dm-inlinecrypt: Add inline encryption support

On Thu, Oct 24, 2024 at 4:11 AM Geoff Back <geoff@...onlair.co.uk> wrote:
>
>
> On 24/10/2024 03:52, Adrian Vovk wrote:
> > On Wed, Oct 23, 2024 at 2:57 AM Christoph Hellwig <hch@...radead.org> wrote:
> >> On Fri, Oct 18, 2024 at 11:03:50AM -0400, Adrian Vovk wrote:
> >>> Sure, but then this way you're encrypting each partition twice. Once by the dm-crypt inside of the partition, and again by the dm-crypt that's under the partition table. This double encryption is ruinous for performance, so it's just not a feasible solution and thus people don't do this. Would be nice if we had the flexibility though.
>
> As an encrypted-systems administrator, I would actively expect and
> require that stacked encryption layers WOULD each encrypt.  If I have
> set up full disk encryption, then as an administrator I expect that to
> be obeyed without exception, regardless of whether some higher level
> file system has done encryption already.
>
> Anything that allows a higher level to bypass the full disk encryption
> layer is, in my opinion, a bug and a serious security hole.

Sure I'm sure there's usecases where passthrough doesn't make sense.
It should absolutely be an opt-in flag on the dm target, so you the
administrator at setup time can choose whether or not you perform
double-encryption (and it defaults to doing so). Because there are
usecases where it doesn't matter, and for those usecases we'd set the
flag and allow passthrough for performance reasons.

- Adrian