Coverity: intel_hti_uses_phy(): Integer handling issues - coverity-bot

From: coverity-bot <keescook@chromium.org>
To: Jani Nikula <jani.nikula@intel.com>
Cc: "Jani Nikula" <jani.nikula@linux.intel.com>,
	"David Airlie" <airlied@gmail.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	"Lucas De Marchi" <lucas.demarchi@intel.com>,
	"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
	intel-gfx@lists.freedesktop.org,
	"Tvrtko Ursulin" <tvrtko.ursulin@linux.intel.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Arun R Murthy" <arun.r.murthy@intel.com>,
	"Imre Deak" <imre.deak@intel.com>,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	linux-next@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Coverity: intel_hti_uses_phy(): Integer handling issues
Date: Fri, 18 Nov 2022 08:49:24 -0800	[thread overview]
Message-ID: <202211180848.D39006C@keescook> (raw)

Hello!

This is an experimental semi-automated report about issues detected by
Coverity from a scan of next-20221118 as part of the linux-next scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified
lines of code (noted below) that were touched by commits:

  Thu Nov 17 16:12:56 2022 +0200
    62749912540b ("drm/i915/display: move hti under display sub-struct")

Coverity reported the following:

*** CID 1527374:  Integer handling issues  (BAD_SHIFT)
drivers/gpu/drm/i915/display/intel_hti.c:24 in intel_hti_uses_phy()
18     	if (INTEL_INFO(i915)->display.has_hti)
19     		i915->display.hti.state = intel_de_read(i915, HDPORT_STATE);
20     }
21
22     bool intel_hti_uses_phy(struct drm_i915_private *i915, enum phy phy)
23     {
vvv     CID 1527374:  Integer handling issues  (BAD_SHIFT)
vvv     In expression "1UL << 2 * phy + 1", shifting by a negative amount has undefined behavior.  The shift amount, "2 * phy + 1", is as little as -1.
24     	return i915->display.hti.state & HDPORT_ENABLED &&
25     		i915->display.hti.state & HDPORT_DDI_USED(phy);
26     }
27
28     u32 intel_hti_dpll_mask(struct drm_i915_private *i915)
29     {

If this is a false positive, please let us know so we can mark it as
such, or teach the Coverity rules to be smarter. If not, please make
sure fixes get into linux-next. :) For patches fixing this, please
include these lines (but double-check the "Fixes" first):

Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527374 ("Integer handling issues")
Fixes: 62749912540b ("drm/i915/display: move hti under display sub-struct")

This code appears to be safe currently (intel_hti_uses_phy() is never
called with PHY_NONE), but perhaps add an explicit check?

	if (WARN_ON(phy == PHY_NONE))
		return false;

Thanks for your attention!

-- 
Coverity-bot