Re: [Intel-gfx] [PATCH v2] drm/i915: Fix invalid access to ACPI _DSM objects

[Takashi Iwai]

On Wed, 07 Apr 2021 23:28:48 +0200,
Ville Syrjälä wrote:
> 
> On Wed, Apr 07, 2021 at 06:56:15PM +0200, Takashi Iwai wrote:
> > On Wed, 07 Apr 2021 18:34:46 +0200,
> > Ville Syrjälä wrote:
> > > 
> > > On Fri, Apr 02, 2021 at 10:23:17AM +0200, Takashi Iwai wrote:
> > > > intel_dsm_platform_mux_info() tries to parse the ACPI package data
> > > > from _DSM for the debug information, but it assumes the fixed format
> > > > without checking what values are stored in the elements actually.
> > > > When an unexpected value is returned from BIOS, it may lead to GPF or
> > > > NULL dereference, as reported recently.
> > > > 
> > > > Add the checks of the contents in the returned values and skip the
> > > > values for invalid cases.
> > > > 
> > > > v1->v2: Check the info contents before dereferencing, too
> > > > 
> > > > BugLink: http://bugzilla.opensuse.org/show_bug.cgi?id=1184074
> > > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > > > ---
> > > >  drivers/gpu/drm/i915/display/intel_acpi.c | 22 ++++++++++++++++++++--
> > > >  1 file changed, 20 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/display/intel_acpi.c b/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > index e21fb14d5e07..833d0c1be4f1 100644
> > > > --- a/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > +++ b/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > @@ -84,13 +84,31 @@ static void intel_dsm_platform_mux_info(acpi_handle dhandle)
> > > >  		return;
> > > >  	}
> > > >  
> > > > +	if (!pkg->package.count) {
> > > > +		DRM_DEBUG_DRIVER("no connection in _DSM\n");
> > > > +		return;
> > > > +	}
> > > > +
> > > >  	connector_count = &pkg->package.elements[0];
> > > >  	DRM_DEBUG_DRIVER("MUX info connectors: %lld\n",
> > > >  		  (unsigned long long)connector_count->integer.value);
> > > >  	for (i = 1; i < pkg->package.count; i++) {
> > > >  		union acpi_object *obj = &pkg->package.elements[i];
> > > > -		union acpi_object *connector_id = &obj->package.elements[0];
> > > > -		union acpi_object *info = &obj->package.elements[1];
> > > > +		union acpi_object *connector_id;
> > > > +		union acpi_object *info;
> > > > +
> > > > +		if (obj->type != ACPI_TYPE_PACKAGE || obj->package.count < 2) {
> > > > +			DRM_DEBUG_DRIVER("Invalid object for MUX #%d\n", i);
> > > > +			continue;
> > > > +		}
> > > > +
> > > > +		connector_id = &obj->package.elements[0];
> > > 
> > > You don't want to check connector_id->type as well?
> > 
> > I added only the minimal checks that may lead to Oops.
> 
> OK. I guess misinterpreting something else as an integer isn't
> particular dangerous in this case.
> 
> Pushed to drm-intel-next. Thanks.

Great, thanks!

> Oh, could you ask the bug reporter to attach an acpidump to the
> bug? Might be good to have that stuff on record somewhere if/when
> someone wants to actually figure out what's going on here.

OK, I'll ask.

> That said, maybe we should just nuke this whole thing instead?
> Unless I'm missing someting this code doesn't seem to actually
> do anything...

Yeah, that looks nothing but showing the debug information and that
can be checked via acpidump output, too...


Takashi