Re: [PATCH alternative 2] block: fix the REQ_OP_SECURE_ERASE handling to not leak erased data

[Ulf Hansson]

On Fri, 18 Mar 2022 at 10:11, Christoph Hellwig <hch@xxxxxx> 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