[PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution

[Wei Liu]

On Sun, Jan 16, 2022 at 09:53:06PM +0000, Haiyang Zhang wrote:
> 
> 
> > -----Original Message-----
> > From: Michael Kelley (LINUX) <mikelley at microsoft.com>
> > Sent: Sunday, January 16, 2022 2:19 PM
> > To: KY Srinivasan <kys at microsoft.com>; Haiyang Zhang <haiyangz at microsoft.com>; Stephen
> > Hemminger <sthemmin at microsoft.com>; wei.liu at kernel.org; Wei Hu <weh at microsoft.com>; Dexuan
> > Cui <decui at microsoft.com>; drawat.floss at gmail.com; hhei <hhei at redhat.com>; linux-
> > kernel at vger.kernel.org; linux-hyperv at vger.kernel.org; linux-fbdev at vger.kernel.org; dri-
> > devel at lists.freedesktop.org
> > Cc: Michael Kelley (LINUX) <mikelley at microsoft.com>
> > Subject: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution
> > 
> > In the WIN10 version of the Synthetic Video protocol with Hyper-V,
> > Hyper-V reports a list of supported resolutions as part of the protocol
> > negotiation. The driver calculates the maximum width and height from
> > the list of resolutions, and uses those maximums to validate any screen
> > resolution specified in the video= option on the kernel boot line.
> > 
> > This method of validation is incorrect. For example, the list of
> > supported resolutions could contain 1600x1200 and 1920x1080, both of
> > which fit in an 8 Mbyte frame buffer.  But calculating the max width
> > and height yields 1920 and 1200, and 1920x1200 resolution does not fit
> > in an 8 Mbyte frame buffer.  Unfortunately, this resolution is accepted,
> > causing a kernel fault when the driver accesses memory outside the
> > frame buffer.
> > 
> > Instead, validate the specified screen resolution by calculating
> > its size, and comparing against the frame buffer size.  Delete the
> > code for calculating the max width and height from the list of
> > resolutions, since these max values have no use.  Also add the
> > frame buffer size to the info message to aid in understanding why
> > a resolution might be rejected.
> > 
> > Fixes: 67e7cdb4829d ("video: hyperv: hyperv_fb: Obtain screen resolution from Hyper-V
> > host")
> > Signed-off-by: Michael Kelley <mikelley at microsoft.com>
[...]
> 
> Reviewed-by: Haiyang Zhang <haiyangz at microsoft.com>
> 

Applied to hyperv-fixes. Thanks.