[Intel-gfx] [PATCH] drm/i915: Check DVO reads for errors

[Chris Wilson]

On Thu, Feb 26, 2015 at 06:47:14PM +0100, Quentin Casasnovas wrote:
> On Thu, Feb 26, 2015 at 05:10:17PM +0000, Chris Wilson wrote:
> > Not all of the DVO functions were checking the return value from their
> > i2c routines when reading registers. This could lead to us feeding
> > garbage values back into the hardware, possible causing further
> > failures. In some cases the uninitialised stack values were being
> > written into the kernel log.
> > 
> > Quentin Casasnovas suggested the simple solution of just initialising
> > the output parameter to zero in all cases, but we may as well spend the
> > extra few moments to fix it correctly.
> 
> I'm not sure your patch would be -stable material mainly because of the
> diffstat.  Given the security implications, I would still rather have my
> patch merged first so it can easily be back-ported to -stable and distro
> kernels easily, and then have your patch on top when it gets properly
> reviewed.  Especially since your patch looks like it's doing other
> not strictly related stuffs like these:

I don't agree that your patch is stable material since it is not
obviously correct (it potentially changes values written to hw), hasn't
been tested and doesn't qualify as a "real bug that impacts people".

To fix the security concerns you expressed, you could have equally
removed the DRM_DEBUG_KMS().
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre