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

[Wei Liu <wei.liu@kernel.org>]

On Mon, Jan 24, 2022 at 10:52:22AM +0100, Helge Deller wrote:
> On 1/23/22 23:30, Wei Liu wrote:
> > On Sun, Jan 23, 2022 at 10:27:56PM +0000, Michael Kelley (LINUX) wrote:
> >> From: Wei Liu <wei.liu@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@microsoft.com>
> >>>>> Sent: Sunday, January 16, 2022 2:19 PM
> >>>>> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> >>> <haiyangz@microsoft.com>; Stephen
> >>>>> Hemminger <sthemmin@microsoft.com>; wei.liu@kernel.org; Wei Hu
> >>> <weh@microsoft.com>; Dexuan
> >>>>> Cui <decui@microsoft.com>; drawat.floss@gmail.com; hhei <hhei@redhat.com>;
> >>> linux-
> >>>>> kernel@vger.kernel.org; linux-hyperv@vger.kernel.org; linux-
> >>> fbdev@vger.kernel.org; dri-
> >>>>> devel@lists.freedesktop.org
> >>>>> Cc: Michael Kelley (LINUX) <mikelley@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@microsoft.com>
> >>> [...]
> >>>>
> >>>> Reviewed-by: Haiyang Zhang <haiyangz@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!
> 
> Linus hasn't pulled my tree yet, and he will probably not before the
> next merge window. So, if this is an urgent bugfix for you, I can offer
> to drop it from the fbdev tree and that you take it through the hyperv-fixes tree.
> In that case you may add an Acked-by: Helge Deller <deller@gmx.de>.
> Just let me know what you prefer.

Hi Helge

Yes, I would like to upstream it as soon as possible so that it can
propagate to stable trees and be backported by downstream vendors.

I will pick it up in hyperv-fixes. Please drop it from your for-next
tree.

Thanks,
Wei.

> 
> Helge