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

[Wei Liu]

On Sun, Jan 23, 2022 at 10:27:56PM +0000, Michael Kelley (LINUX) wrote:
> From: Wei Liu <wei.liu at kernel.org> Sent: Sunday, January 23, 2022 1:56 PM
> > 
> > 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.
> 
> This fix got pulled into the fbdev/for-next tree by a new maintainer, Helge Deller.
> See https://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git/commit/?h=for-next&id=bcc48f8d980b12e66a3d59dfa1041667db971d86

OK. I will drop it from hyperv-fixes. Thanks for letting me know!

> 
> Michael