linux-kernel - Re: [PATCH alternative 2] block: fix the REQ_OP_SECURE

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Message-ID: <CAPDyKFohNVnrwcZSCGnv7X++FfQ0a3rdeMx3tvJ0eW-Afr9Tyg@mail.gmail.com>
Date:   Fri, 18 Mar 2022 11:36:04 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, jaegeuk@...nel.org, chao@...nel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Daeho Jeong <daehojeong@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org
Subject: Re: [PATCH alternative 2] block: fix the REQ_OP_SECURE_ERASE handling
 to not leak erased data

On Fri, 18 Mar 2022 at 10:11, Christoph Hellwig <hch@....de> wrote:
>
> On Thu, Mar 17, 2022 at 10:44:01AM +0100, Ulf Hansson wrote:
> > Stating that it can't work is probably not a correct statement.
> > Certainly it can, but it depends on how "secure" (or clever) the
> > implementation of the FTL is in the flash media. I mean, nothing
> > prevents the FTL from doing a real erase on erase block level and
> > simply let the "secure erase" request wait on that operation to be
> > completed.
>
> Well, that assumes it can find all the previous copied of the data.
> Having worked with various higher end SSDs FTLs I know they can't,
> so if an eMMC device could that would very much surpise me given
> the overhead.

An eMMC is no different from an SSD in this regard, so you are most
definitely correct. BTW, I was one of those guys working with FTLs
myself, but it was a long time ago, when NAND/NOR flashes were less
complicated to manage.

Anyway, to really make things work, one would need some additional low
level partitioning  - or commands to tag the data for special
purposes. eMMCs do have some support for things like this, but whether
it actually works to serve this particular use case (secure erase), I
really can't tell.

Kind regards
Uffe