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    SubjectRe: [PATCH 5.15 015/110] vhost: fix hung thread due to erroneous iotlb entries
    Mon, Mar 14, 2022 at 12:53:17PM +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
    >
    >
    >

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