Re: [PATCH 5.16 017/121] vhost: fix hung thread due to erroneous iotlb entries

Anirudh Rayabharam
2022-03-14T16:21:41Z

On Mon, Mar 14, 2022 at 12:53:20PM +0100, Greg Kroah-Hartman wrote:
> From: Anirudh Rayabharam <mail@anirudhrb.com>
>
> [ Upstream commit e2ae38cf3d91837a493cb2093c87700ff3cbe667 ]

This breaks batching of IOTLB messages. [1] fixes it but hasn't landed in
Linus' tree yet.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?h=linux-next&id=95932ab2ea07b79cdb33121e2f40ccda9e6a73b5

- Anirudh.
>
> In vhost_iotlb_add_range_ctx(), range size can overflow to 0 when
> start is 0 and last is ULONG_MAX. One instance where it can happen
> is when userspace sends an IOTLB message with iova=size=uaddr=0
> (vhost_process_iotlb_msg). So, an entry with size = 0, start = 0,
> last = ULONG_MAX ends up in the iotlb. Next time a packet is sent,
> iotlb_access_ok() loops indefinitely due to that erroneous entry.
>
> Call Trace:
> <TASK>
> iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
> vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
> vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
> vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
> kthread+0x2e9/0x3a0 kernel/kthread.c:377
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> </TASK>
>
> Reported by syzbot at:
> https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87
>
> To fix this, do two things:
>
> 1. Return -EINVAL in vhost_chr_write_iter() when userspace asks to map
> a range with size 0.
> 2. Fix vhost_iotlb_add_range_ctx() to handle the range [0, ULONG_MAX]
> by splitting it into two entries.
>
> Fixes: 0bbe30668d89e ("vhost: factor out IOTLB")
> Reported-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> Link: https://lore.kernel.org/r/20220305095525.5145-1-mail@anirudhrb.com
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/vhost/iotlb.c | 11 +++++++++++
> drivers/vhost/vhost.c | 5 +++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c
> index 670d56c879e5..40b098320b2a 100644
> --- a/drivers/vhost/iotlb.c
> +++ b/drivers/vhost/iotlb.c
> @@ -57,6 +57,17 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
> if (last < start)
> return -EFAULT;
>
> + /* If the range being mapped is [0, ULONG_MAX], split it into two entries
> + * otherwise its size would overflow u64.
> + */
> + if (start == 0 && last == ULONG_MAX) {
> + u64 mid = last / 2;
> +
> + vhost_iotlb_add_range_ctx(iotlb, start, mid, addr, perm, opaque);
> + addr += mid + 1;
> + start = mid + 1;
> + }
> +
> if (iotlb->limit &&
> iotlb->nmaps == iotlb->limit &&
> iotlb->flags & VHOST_IOTLB_FLAG_RETIRE) {
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 59edb5a1ffe2..55475fd59fb7 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1170,6 +1170,11 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
> goto done;
> }
>
> + if (msg.size == 0) {
> + ret = -EINVAL;
> + goto done;
> + }
> +
> if (dev->msg_handler)
> ret = dev->msg_handler(dev, &msg);
> else
> --
> 2.34.1
>
>
>