Re: [PATCH v7] mmc: Add mmc CMD+ACMD passthrough ioctl

[Arnd Bergmann <arnd@arndb.de>]

On Friday 22 April 2011, John Calixto wrote:
> Allows appropriately-privileged applications to send CMD (normal) and
> ACMD (application-specific; preceded with CMD55) commands to
> cards/devices on the mmc bus.  This is primarily useful for enabling the
> security functionality built in to every SD card.
> 
> It can also be used as a generic passthrough (e.g. to enable virtual
> machines to control mmc bus devices directly).  However, this use case
> has not been tested rigorously.  Generic passthrough testing was only
> conducted for a few non-security opcodes to prove the feasibility of the
> passthrough.
> 
> Since any opcode can be sent using this passthrough, it is very possible
> to render the card/device unusable.  Applications that use this ioctl
> must have CAP_SYS_RAWIO.
> 
> Security commands tested on TI PCIxx12 (SDHCI), Sigma Designs SMP8652
> SoC, TI OMAP3621 SoC, TI OMAP3630 SoC, Samsung S5PC110 SoC, Qualcomm
> MSM7200A SoC.
> 
> Signed-off-by: John Calixto <john.calixto@modsystems.com>
> Reviewed-by: Andrei Warkentin <andreiw@motorola.com>

The implementation looks good to me now,

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

I'll leave the final decision whether this is a good feature to have
to Chris. I still believe that we should have per-command ioctls
for the security feature, but getting there would require someone
to implement it, and I'm not going to do that.

	Arnd