Re: [PATCH v2 -mm 4/6] ide: avoid DMA on the stack for REQ_TYPE_ATA_PC

[Borislav Petkov <petkovbb@googlemail.com>]

On Thu, Jun 05, 2008 at 11:10:48AM -0500, James Bottomley wrote:
> On Mon, 2008-06-02 at 15:57 +0900, FUJITA Tomonori wrote:
> > Some REQ_TYPE_ATA_PC commands uses the stack buffers for DMA, which
> > leads to memory corruption on a non-coherent platform.
> > 
> > With regard to alignment and padding, ide-cd has the the dma safe
> > check for sg requests and REQ_TYPE_ATA_PC. This adds the stack buffer
> > check to that check.
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> > Cc: Borislav Petkov <petkovbb@gmail.com>
> > Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> > ---
> >  drivers/ide/ide-cd.c |    5 +++++
> >  1 files changed, 5 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
> > index e3f085c..e12d602 100644
> > --- a/drivers/ide/ide-cd.c
> > +++ b/drivers/ide/ide-cd.c
> > @@ -1195,6 +1195,7 @@ static ide_startstop_t cdrom_do_block_pc(ide_drive_t *drive, struct request *rq)
> >  		struct request_queue *q = drive->queue;
> >  		unsigned int alignment;
> >  		unsigned long addr;
> > +		unsigned long stack_mask = ~(THREAD_SIZE - 1);
> >  
> >  		if (rq->bio)
> >  			addr = (unsigned long)bio_data(rq->bio);
> > @@ -1212,6 +1213,10 @@ static ide_startstop_t cdrom_do_block_pc(ide_drive_t *drive, struct request *rq)
> >  		alignment = queue_dma_alignment(q) | q->dma_pad_mask;
> >  		if (addr & alignment || rq->data_len & alignment)
> >  			info->dma = 0;
> > +
> > +		if (!((addr & stack_mask) ^
> > +		      ((unsigned long)current->stack & stack_mask)))
> 
> That can basically become
> 
> if ((addr & stack_mask)  == ((unsigned long)current->stack & stack_mask))
> 
> to be a bit clearer, can't it?

yep, yep. Clearer it is :).
> 
> I'm also not keen on the use of current->stack.  It looks like this
> commit:
> 
> commit f7e4217b007d1f73e7e3cf10ba4fea4a608c603f
> Author: Roman Zippel <zippel@linux-m68k.org>
> Date:   Wed May 9 02:35:17 2007 -0700
> 
>     rename thread_info to stack
> 
> Introduced a task_stack_page() accessor to get this instead, so perhaps
> we should use it (I've cc'd Roman and linux-arch for opinions).
> 
> > +			info->dma = 0;
> >  	}
> >  
> >  	/* start sending the command to the drive */
> 
> James
> 

-- 
Regards/Gruß,
    Boris.