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

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Date:   Tue, 23 Nov 2021 15:24:28 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Wolfram Sang <wsa@...nel.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        jie.deng@...el.com, 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 23-11-21, 10:52, Wolfram Sang wrote:
> 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!
> 

Thanks, I completely forgot replying to the last email from Vincent.

FWIW,

Reviewed-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh