ide: avoid DMA on the stack for REQ_TYPE_ATA_PC

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>
Acked-by: Borislav Petkov <petkovbb@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-cd.c

@@ -1195,6 +1195,7 @@ static ide_startstop_t cdrom_do_block_pc(ide_drive_t *drive, struct request *rq)
 		int mask = drive->queue->dma_alignment;
 		unsigned long addr =
 			(unsigned long)page_address(bio_page(rq->bio));
+		unsigned long stack_mask = ~(THREAD_SIZE - 1);
 
 		info->dma = drive->using_dma;
 
@@ -1206,6 +1207,10 @@ static ide_startstop_t cdrom_do_block_pc(ide_drive_t *drive, struct request *rq)
 		 */
 		if ((rq->data_len & 15) || (addr & mask))
 			info->dma = 0;
+
+		if (!((addr & stack_mask) ^
+		      ((unsigned long)current->stack & stack_mask)))
+			info->dma = 0;
 	}
 
 	/* start sending the command to the drive */