linux-kernel - Re: [PATCH v2 1/2] i2c: virtio: disable timeout handling

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Date:   Tue, 23 Nov 2021 10:52:05 +0100
From:   Wolfram Sang <wsa@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     jie.deng@...el.com, viresh.kumar@...aro.org,
        conghui.chen@...el.com, mst@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...s.com
Subject: Re: [PATCH v2 1/2] i2c: virtio: disable timeout handling

On Thu, Nov 11, 2021 at 05:04:11PM +0100, Vincent Whitchurch wrote:
> 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@...el.com>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>

Applied to for-current, thanks!


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