[PATCH] virtio_blk: avoid DMA to stack for the sense buffer

From	Christoph Hellwig <hch@lst.de>
Newsgroups	linux.kernel
Subject	[PATCH] virtio_blk: avoid DMA to stack for the sense buffer
Date	2017-01-04 06:30 +0100
Message-ID	<sVMj7-di-9@gated-at.bofh.it> (permalink)
References	<sVMj7-di-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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@lst.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;
-- 
2.1.4

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[PATCH] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig <hch@lst.de> - 2017-01-04 06:30 +0100
  Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer Jason Wang <jasowang@redhat.com> - 2017-01-04 08:50 +0100
    Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig <hch@lst.de> - 2017-01-09 14:40 +0100
      Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer Jens Axboe <axboe@kernel.dk> - 2017-01-09 17:00 +0100
  Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer 王金浦 <jinpuwang@gmail.com> - 2017-01-04 16:50 +0100
    Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig <hch@lst.de> - 2017-01-05 11:00 +0100
      Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer 王金浦 <jinpuwang@gmail.com> - 2017-01-05 11:50 +0100
        Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig <hch@lst.de> - 2017-01-05 12:20 +0100
  Re: [PATCH] virtio_blk: avoid DMA to stack for the sense buffer "Michael S. Tsirkin" <mst@redhat.com> - 2017-01-09 17:40 +0100

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