Re: [PATCH] block: Clear kernel memory before copying to user

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On Thu, Nov 8, 2018 at 12:12 AM Keith Busch <keith.busch@xxxxxxxxx> wrote:
>
> On Thu, Nov 08, 2018 at 12:03:41AM +0800, Ming Lei wrote:
> > On Wed, Nov 7, 2018 at 11:47 PM Keith Busch <keith.busch@xxxxxxxxx> wrote:
> > >
> > > On Wed, Nov 07, 2018 at 11:44:59PM +0800, Ming Lei wrote:
> > > > blk_update_request() may tell us how much progress made, :-)
> > >
> > > Except when it doesn't, which is 100% of the time for many block
> > > drivers, including nvme.
> >
> > Please look at blk_mq_end_request()(<- nvme_complete_rq()), which
> > calls blk_update_request().
>
> Huh? That just says 100% of the request size was transerred no matter
> what was actually transferred.
>
> The protocol doesn't have a way to express what transfer size occured
> with a command's completion, and even it did, there's no way I'd trust
> every firmware not to screw it.

That sounds something like below:

1) userspace requires to read 8 sectors starting from sector 0
2) nvme tells hardware to do that, and hardware transfers only 4
sectors(0~3) data
to memory, but still tells driver we have done 8 sectors(0~7).

What if there are real data in sectors 4~7?

Is it NVMe specific issue or common problem in other storage hardware?  SCSI
does call blk_update_request() and handles partial completion.

Thanks,
Ming Lei



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