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

From: Wei Liu <wei.liu@kernel.org>
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
	KY Srinivasan <kys@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"wei.liu@kernel.org" <wei.liu@kernel.org>,
	Wei Hu <weh@microsoft.com>, Dexuan Cui <decui@microsoft.com>,
	"drawat.floss@gmail.com" <drawat.floss@gmail.com>,
	hhei <hhei@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 1/1] video: hyperv_fb: Fix validation of screen resolution
Date: Sun, 23 Jan 2022 21:56:06 +0000	[thread overview]
Message-ID: <20220123215606.fzycryooluavtar4@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <MN2PR21MB1295CE3BD15D4EB257A158DCCA569@MN2PR21MB1295.namprd21.prod.outlook.com>

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.