Re: [Intel-gfx] [PATCH 1/5] drm/i915/opregion: check port number bounds for SWSCI display power state

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 13 Jan 2022, Lucas De Marchi <lucas.demarchi@intel.com> wrote:
> On Thu, Jan 13, 2022 at 01:18:03PM +0200, Jani Nikula wrote:
>>The mapping from enum port to whatever port numbering scheme is used by
>>the SWSCI Display Power State Notification is odd, and the memory of it
>>has faded. In any case, the parameter only has space for ports numbered
>>[0..4], and UBSAN reports bit shift beyond it when the platform has port
>>F or more.
>>
>>Since the SWSCI functionality is supposed to be obsolete for new
>>platforms (i.e. ones that might have port F or more), just bail out
>>early if the mapped and mangled port number is beyond what the Display
>>Power State Notification can support.
>>
>>Fixes: 9c4b0a683193 ("drm/i915: add opregion function to notify bios of encoder enable/disable")
>>Cc: <stable@vger.kernel.org> # v3.13+
>>Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4800
>>Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>>---
>> drivers/gpu/drm/i915/display/intel_opregion.c | 15 +++++++++++++++
>> 1 file changed, 15 insertions(+)
>>
>>diff --git a/drivers/gpu/drm/i915/display/intel_opregion.c b/drivers/gpu/drm/i915/display/intel_opregion.c
>>index af9d30f56cc1..ad1afe9df6c3 100644
>>--- a/drivers/gpu/drm/i915/display/intel_opregion.c
>>+++ b/drivers/gpu/drm/i915/display/intel_opregion.c
>>@@ -363,6 +363,21 @@ int intel_opregion_notify_encoder(struct intel_encoder *intel_encoder,
>> 		port++;
>> 	}
>>
>>+	/*
>>+	 * The port numbering and mapping here is bizarre. The now-obsolete
>>+	 * swsci spec supports ports numbered [0..4]. Port E is handled as a
>>+	 * special case, but port F and beyond are not. The functionality is
>>+	 * supposed to be obsolete for new platforms. Just bail out if the port
>>+	 * number is out of bounds after mapping.
>>+	 */
>>+	if (port > 4) {
>>+		drm_dbg_kms(&dev_priv->drm,
>>+			    "[ENCODER:%d:%s] port %c (index %u) out of bounds for display power state notification\n",
>>+			    intel_encoder->base.base.id, intel_encoder->base.name,
>>+			    port_name(intel_encoder->port), port);
>
> Do we need this log message? It will always trigger for platforms with
> PORT F and callers simply ignore the return value.

It will trigger for patch 1, and the stable backport, but, with any luck
and proper opregions, it will be silenced by the subsequent patches.

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Graphics Center