i2c: virtio: disable timeout handling
authorVincent Whitchurch <vincent.whitchurch@axis.com>
Thu, 11 Nov 2021 16:04:11 +0000 (17:04 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 1 Dec 2021 08:04:50 +0000 (09:04 +0100)
[ Upstream commit 84e1d0bf1d7121759622dabf8fbef4c99ad597c5 ]

If a timeout is hit, it can result is incorrect data on the I2C bus
and/or memory corruptions in the guest since the device can still be
operating on the buffers it was given while the guest has freed them.

Here is, for example, the start of a slub_debug splat which was
triggered on the next transfer after one transfer was forced to timeout
by setting a breakpoint in the backend (rust-vmm/vhost-device):

 BUG kmalloc-1k (Not tainted): Poison overwritten
 First byte 0x1 instead of 0x6b
 Allocated in virtio_i2c_xfer+0x65/0x35c age=350 cpu=0 pid=29
  __kmalloc+0xc2/0x1c9
  virtio_i2c_xfer+0x65/0x35c
  __i2c_transfer+0x429/0x57d
  i2c_transfer+0x115/0x134
  i2cdev_ioctl_rdwr+0x16a/0x1de
  i2cdev_ioctl+0x247/0x2ed
  vfs_ioctl+0x21/0x30
  sys_ioctl+0xb18/0xb41
 Freed in virtio_i2c_xfer+0x32e/0x35c age=244 cpu=0 pid=29
  kfree+0x1bd/0x1cc
  virtio_i2c_xfer+0x32e/0x35c
  __i2c_transfer+0x429/0x57d
  i2c_transfer+0x115/0x134
  i2cdev_ioctl_rdwr+0x16a/0x1de
  i2cdev_ioctl+0x247/0x2ed
  vfs_ioctl+0x21/0x30
  sys_ioctl+0xb18/0xb41

There is no simple fix for this (the driver would have to always create
bounce buffers and hold on to them until the device eventually returns
the buffers), so just disable the timeout support for now.

Fixes: 3cfc88380413d20f ("i2c: virtio: add a virtio i2c frontend driver")
Acked-by: Jie Deng <jie.deng@intel.com>
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
drivers/i2c/busses/i2c-virtio.c

index f10a603..7b2474e 100644 (file)
@@ -106,11 +106,10 @@ static int virtio_i2c_prepare_reqs(struct virtqueue *vq,
 
 static int virtio_i2c_complete_reqs(struct virtqueue *vq,
                                    struct virtio_i2c_req *reqs,
-                                   struct i2c_msg *msgs, int num,
-                                   bool timedout)
+                                   struct i2c_msg *msgs, int num)
 {
        struct virtio_i2c_req *req;
-       bool failed = timedout;
+       bool failed = false;
        unsigned int len;
        int i, j = 0;
 
@@ -132,7 +131,7 @@ static int virtio_i2c_complete_reqs(struct virtqueue *vq,
                        j++;
        }
 
-       return timedout ? -ETIMEDOUT : j;
+       return j;
 }
 
 static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
@@ -141,7 +140,6 @@ static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
        struct virtio_i2c *vi = i2c_get_adapdata(adap);
        struct virtqueue *vq = vi->vq;
        struct virtio_i2c_req *reqs;
-       unsigned long time_left;
        int count;
 
        reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
@@ -164,11 +162,9 @@ static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
        reinit_completion(&vi->completion);
        virtqueue_kick(vq);
 
-       time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
-       if (!time_left)
-               dev_err(&adap->dev, "virtio i2c backend timeout.\n");
+       wait_for_completion(&vi->completion);
 
-       count = virtio_i2c_complete_reqs(vq, reqs, msgs, count, !time_left);
+       count = virtio_i2c_complete_reqs(vq, reqs, msgs, count);
 
 err_free:
        kfree(reqs);