linux-kernel - RE: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution

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Message-ID: <MWHPR21MB1593ED650DA82BC3009F66CED75D9@MWHPR21MB1593.namprd21.prod.outlook.com>
Date:   Sun, 23 Jan 2022 22:27:56 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Wei Liu <wei.liu@...nel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Hu <weh@...rosoft.com>, Dexuan Cui <decui@...rosoft.com>,
        "drawat.floss@...il.com" <drawat.floss@...il.com>,
        hhei <hhei@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: RE: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution

From: Wei Liu <wei.liu@...nel.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@...rosoft.com>
> > > Sent: Sunday, January 16, 2022 2:19 PM
> > > To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; Stephen
> > > Hemminger <sthemmin@...rosoft.com>; wei.liu@...nel.org; Wei Hu
> <weh@...rosoft.com>; Dexuan
> > > Cui <decui@...rosoft.com>; drawat.floss@...il.com; hhei <hhei@...hat.com>;
> linux-
> > > kernel@...r.kernel.org; linux-hyperv@...r.kernel.org; linux-
> fbdev@...r.kernel.org; dri-
> > > devel@...ts.freedesktop.org
> > > Cc: Michael Kelley (LINUX) <mikelley@...rosoft.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@...rosoft.com>
> [...]
> >
> > Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.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

Michael