linux-hardening - Coverity: intel_hti_uses_phy(): Integer handling issues

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

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@...omium.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