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

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

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);
+		return -EINVAL;
+	}
+
 	if (!enable)
 		parm |= 4 << 8;
 
-- 
2.30.2