On Thu, Dec 22, 2016 at 04:03:56PM -0800, Chris Leech wrote:
> Of course, looks like I've screwed up my bisect run on this so I'm still
> taking a look. It triggers for me with 'hdparm -B /dev/vda' but may
> also depend on kernel configuration.
>
> I started with the fedora rawhide config with a lot of debug on and
> trimed it down with a localmodconfig run in the VM to speed up rebuilds.
I think the configuration dependency is CONFIG_HAVE_ARCH_VMAP_STACK,
I've just reproduce the issue with it, and the backtrace points to
__virtblk_add_req when setting up the sense buffer. And it turns out
that blk_execute_rq tries to do I/O to the on-stack sense buffer.
At least SCSI always has a kmalloced sense buffer, so I guess we'll
need something similar for virtio_blk for now. For 4.11 I plan to
rework how BLOCK_PC commands work entirely, so hopefull we can make
the sense buffer handling a lot less wasteful.
---
>From 0a77bc424ed907c1e99b4756bb498370b498183a Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@xxxxxx>
Date: Fri, 23 Dec 2016 10:57:06 +0100
Subject: virtio_blk: avoid DMA to stack for the sense buffer
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@xxxxxx>
---
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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