linux-kernel - Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer

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Date:   Wed, 4 Jan 2017 15:44:40 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Christoph Hellwig <hch@....de>, axboe@...nel.dk, mst@...hat.com
Cc:     linux-block@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer



On 2017年01月04日 13:25, Christoph Hellwig wrote:
> Most users of BLOCK_PC requests allocate the sense buffer on the stack,
> so to avoid DMA to the stack copy them to a field in the heap allocated
> virtblk_req structure.  Without that any attempt at SCSI passthrough I/O,
> including the SG_IO ioctl from userspace will crash the kernel.  Note that
> this includes running tools like hdparm even when the host does not have
> SCSI passthrough enabled.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   drivers/block/virtio_blk.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 5545a67..3c3b8f6 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -56,6 +56,7 @@ struct virtblk_req {
>   	struct virtio_blk_outhdr out_hdr;
>   	struct virtio_scsi_inhdr in_hdr;
>   	u8 status;
> +	u8 sense[SCSI_SENSE_BUFFERSIZE];
>   	struct scatterlist sg[];
>   };
>   
> @@ -102,7 +103,8 @@ static int __virtblk_add_req(struct virtqueue *vq,
>   	}
>   
>   	if (type == cpu_to_virtio32(vq->vdev, VIRTIO_BLK_T_SCSI_CMD)) {
> -		sg_init_one(&sense, vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
> +		memcpy(vbr->sense, vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
> +		sg_init_one(&sense, vbr->sense, SCSI_SENSE_BUFFERSIZE);
>   		sgs[num_out + num_in++] = &sense;
>   		sg_init_one(&inhdr, &vbr->in_hdr, sizeof(vbr->in_hdr));
>   		sgs[num_out + num_in++] = &inhdr;

Acked-by: Jason Wang <jasowang@...hat.com>